国立研究開発法人国立国際医療研究センター

国際医療協力局

テクニカル・レポート

vol.

05

March, 2014

ラオス人民民主共和国におけるB 型肝炎有病率調査

Hepatitis B Prevalence Survey
in Lao PDRISBN 978-4-909675-19-4

目次 / Table of Contents
ラオス人民民主共和国における B 型肝炎有病率調査

Hepatitis B Prevalence Survey in Lao PDR
目次 / Table of Contents

03

ラオス人民民主共和国における B 型肝炎有病率調査

05

謝辞

06

略語

07

サマリー

08

1．はじめに

09

2. 方法

10

3. 結果

13

4. 考察と結論

16

文献

18

Hepatitis B Prevalence Survey in Lao PDR

21

Acknowledgements

22

Acronyms

23

Executive Summary24

1. Introduction25

2. Methods

26

3. Results

29

4. Discussion and recommendations

32

References

34

資料 / Annexes35

資料 1: 選択された郡と村 / Annex 1: Selected districts and villages36

資料 2: 質問票 / Annex 2: Questionnaire37

資料 3: 説明文書と同意書 / Annex 3: Informed Consent form

43

資料 4: トレーニング内容 / Annex 4: Training agenda

46

資料 5: 監督者と調査員 / Annex 5: Supervisors and surveyors

47

資料 6: 掲載論文 / Annex 6. Publication

49

3

ラオス人民民主共和国におけるB 型肝炎有病率調査

謝辞

謝辞

研究の遂行にあたりご指導、ご助言くださった皆様にお礼申し上げます。

ラオス人民民主共和国 保健省
予防接種課 (National Immunization Program)
国立検査疫学センター (National Center for Laboratory & Epidemiology)
国立国際医療研究センター
国際医療協力局
肝炎・免疫研究センター 肝疾患研究部
国立感染症研究所
ウイルス第 2 部JICA( 国際協力機構 ) プロジェクト
保健セクター事業調整能力強化プロジェクトフェーズ 2
母子保健統合サービス強化プロジェクト
母子保健人材開発プロジェクト
世界保健機関西太平洋地域事務所
ラオス事務所

6

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

略語

略語

C.I.
DPT-HepB
EPI

Confidence interval

信頼区間

Diphtheria, pertussis, tetanus, hepatitis B vaccine
シフテリア、百日咳、破傷風、B 型肝炎ワクチン
Expanded Programme on Immunization
拡大予防接種計画

HB

Hepatitis B

HBs 抗原

Hepatitis B surface antigen

ID

Identification number

JICA

Japan International Cooperation Agency

NCGM
NCLE

B 型肝炎
B 型肝炎ウイルス表面抗原

識別番号
国際協力機構National Center for Global Health and Medicine
国立国際医療研究センター
National Center for Laboratory and Epidemiology
国立検査疫学センター

NIP

National immunization Program

国家予防接種課

PPS

Probability proportionate to size

確率比例抽出SBA

Skilled birth attendance

VPD

Vaccine preventable diseases

WHO

World Health Organization

熟練助産師
ワクチン予防可能疾患
世界保健機関テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

7

サマリー

サマリー

⿇⿇ 背景

診断を行った。

る B 型肝炎の有病率を調べ、B 型肝炎ワクチン導入の効果

⿇⿇ 結果

ラオス人民民主共和国 ( 以下、ラオス ) の一般人口におけを評価するため、ラオス保健省と国立国際医療研究センター( 以 下、NCGM) は血清診断および質問票による横断調査をを収集し、HBs 抗原陽性率

実施することになった。調査は 2012 年 2 月に全国規模では 5~9 歳の小児において 1.7% (95%C.I.=0.8, 2.6)、妊娠可行われた。本報告書は調査結果をまとめたものである。

能年齢の母親において 2.9% (95%C.I.=1.6, 4.2) と推定された。子どもの HBs 抗原陽性は母親の HB 感染と有意に相関⿇⿇ 目的していたが、他の可能性のある危険因子 ( 母親の年齢、人種、調査目的は以下の通りである。

1.

小児における B 型肝炎ウイルス表面抗原 (HBs 抗原 ) 陽
性率を推定する

2.

母親における HBs 抗原陽性率を推定する

3.

可能性のある危険因子を評価する

⿇⿇ 対象年齢、地域、調査時期
年齢

最寄りの保健センターまでの 時間、母親の教育レベル、既往歴 ) とは相関していなかった。
⿇⿇ 考察および推奨

本研究はラオスにおける初めての全国 B 型肝炎有病率調査である。調査結果から推定される有病率は、周辺国から報告されている値より低かったが、その理由は不明である。

小児

5~9 歳

B 型肝炎ワクチンの出生時接種と乳児期の 3 回接種は依然

母親

15~45 歳として重要と考えられる ; それゆえ、国家予防接種事業を注

地域

全国

時期

2012 年 1~2 月

⿇⿇ 調査方法全国 143 郡を 2 つの層に分けた ;2010 年の接種率データ

を用い、3 回目のジフテリア、百日咳、破傷風、B 型肝炎ワ
クチン (DPT-HepB) の接種率が高い郡と低い郡である。次に確率比例抽出により各層から無作為に 12 郡を選択し、さらに確率比例抽出により各郡から 2 村を選択した。それ
ぞれの村 ( クラスター ) において、調査員が住民台帳から無作為に 21 の母子ペアを選んだ。選ばれた母子に対し調査の目的と方法、個人情報保持について説明し、同意が得られたのち、質問票および血液採取を実施した。血液はDetermine® 迅速 診断キット（日本名：ダイナスクリーン・
HBsAg Ⅱ、アリーアメディカル社）を使用して HBs 抗原の8

計 2,016 の血液検体 ( 小児 1,008 例、および母親 1,008 例 )テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

意深く監視し、繰り返し調査をすることが必要であろう。

1. はじめに1. はじめに⿇⿇ 背景

B 型肝炎 (HB) ウイルス感染者は世界中で 20 億人を超え、

表 1. ラオスにおける B 型肝炎予防接種活動

毎年約 100 万人が HB ウイルス 感染により死亡している [1, 2]。

2002 年

定期予防接種として DTP-HepB2005 年

2 つの南部県の病院を追加

2004 年

そのうち 33% は肝細胞癌、残りは肝疾患の末期合併症による。世界保健機関 (WHO) の西太平洋地域事務局は、2003
年に決議案 WPR/RC54.R3 を、2005 年に決議案 WPR/RC56.

2007 年R8 を採択し、5 歳児の慢性 B 型肝炎感染を 1% 未満に減らすという最終的な地域目標に向けた中間目標として、2012
年までにその感染率を 2% 未満に低下させることを提唱した。B 型肝炎コントロール戦略の地域での進展は、小児の B

残りの県と全 123 郡の病院を追加

2009 年

9 つの県の 50 郡において、保健セン
ター職員による B 型肝炎出生時接種
後の家庭 訪問を開始

2010 年

ラオス人民民主共和国 ( 以下 , ラオス ) は、1984 年に特定の地域において拡大予防接種 計画 (EPI) を開始した。こ8 つの県の病院を追加

2008 年

型肝炎感染の劇的な低下をもたらし、上記の中間目標は 27の国と地域で達成が期待されている (WPR/RC61/10)。

首都の病院に出生時接種を導入

施設での勤務および家庭分娩への立ち会いが可能な熟練した助産師 ( 専門の技 能を持つ分娩介助者 ) の訓練のプログラムは、1994 年に規模が全国に拡大された。B 型
肝炎 ワクチンは 2002 年に EPI に加えられ、徐々に拡大された ( 表 1)。カンボジア、中国、タイ、ベトナムなどの近隣諸国の研究により B 型肝炎ウイルス表面抗原 (HBs 抗原 )⿇⿇ 調査の目的

調査の主目的は、以下の通りである。

、これまでラ1.

小児における HBs 抗原の陽性率を推定する

オスの一般住民における慢性 B 型肝炎ウイルス有病率に関

2.

母親における HBs 抗原の陽性率を推定する

する報告はなされていない。したがって、現状を理解する

3.

可能性のある危険因子を評価する

陽性率が高いことが明らかになったが[3, 4, 5, 6]

ため、そして母子感染予防を目標とする予防接種普及政策を評価するために、一般住民を対象とした B 型肝炎の血清陽性率調査が必要である [7, 8]。
ラオス保健省と国立国際医療研究センター (NCGM) は、
血清陽性率調査について合意した。チームは、2011 年の 1
月と 2 月にパイロット調査としてラオスの中央部に集中し、2012 年の 1 月 ~2 月には国全体を対象とした。

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

92. 方法2. 方法

⿇⿇ 標本サイズ算出

望ましい信頼度レベル 1.96、許容誤差 0.02、HBs 抗原陽

セットとガラス毛細管を用いた。Determine® 簡易試験を行
うには、約 50 μ l の血液が必要である。

性率 0.05、デザイン効果 2.0、階 層数 2 および回答率 0.95

調査では、参加者の性、年齢と生年月日、居住地、社会と想定して、必要な標本サイズを 961 と計算した。これは、的要因、肝炎の家族歴、予防接 種歴および B 型肝炎感染の961 組の母子 (1,922 例 ) を意味する。実施を容易にするため、潜在的危険因子を確認する質問票を用いた。

母子 1,008 組 (2,016 例 ) の収集 を計画した。
⿇⿇ サンプリング法

多段階層化収束抽出法を用いて、妊娠可能年齢の母親とその子供を選出した。
ラオスは首都ビエンチャンと 16 の県からなる国である。
2005 年の国勢調査によると、国 内には 143 の郡があり、10,000 を超える村がある。われわれは、
ジフテリア、
百日咳、

選択されなかった村で予備調査を実施した後、本調査直前に調査員に対する 2 日間の研修が行われた。研修には国レベル・県レベルの監督者も参加した。研修講師は、国家
予防接 種課 (NIP) と国立検査疫学センター (NCLE) から採用した。
⿇⿇ Determine® を用いた HBsAg 検出

Determine®(Arlier, Japan) を用いて HBs 抗原を測定した。

破傷風、
B 型肝炎ワクチン (DPT-HepB) 3 回目の接種率によっこの検査は、血液を検体パッドに載せた後に追跡液を加えて、全郡を高接種率 ( ≧ 76%, 72 郡 ) と低接種率 (<76%,71

ると、15 分 ~24 時間後に、結果を読むことができる、とい郡 ) の 2 層に分けた。第 1 段階として、
確率比例抽出法 (PPS)

うものである。

を用いて、各層から 12 郡を無作為に選択した。第 2 段階では、PPS により各郡から 2 つの村を無作為に選択した。48
村のそれぞれにおいて、貧困削減プログラムによる居住者

⿇⿇ データ入力と分析

全情報をエクセルファイルシートに入力し、データに

リスト に基づいて、対象世帯リストを作成した。貧困削減

誤りが無いように二重チェックを行った。STATA ver. 12.0

プログラムのリストが利用不能の場合 は、選択された村を(Stata Corp., College Station, Tx, USA) により、結果を分析

調査チームが訪れた際に、EPI リストまたは関連する居住者し た。

リストを使 用した。紙のくじ引き法を用いて、21 組の母子が無作為に選択された。
質問票と血液採取に要する時間は一組あたり 20 分と予測

⿇⿇ 倫理

リスクを最小にするために、新品の使い捨て安全ランセッ

され、また村内および村間の移動は困難であることが多い

トを用いて血液サンプルを採 取した。監督者と調査員は、

ので、1 調査チームあたり 1 日に 6 組が適当であると考え研修会で訓練を受けた。調査員は製造者の説明書に従い、られた。各チーム 2 名の調査員からなる 24 の調査チームが各 参加者に対してゴム手袋を使用した。使用の直後に、す組織された。

べての安全ランセットと綿球をセーフティボックスに回収

⿇⿇ データ収集した。
調査を実施する前に、地元当局 ( 村のリーダーと地域の血液サンプルは、訓練を受けた調査員が、選択された村女性同盟の会長 ) および選出さ れた小児の両親または保護において指尖を穿刺し採取した。 血液採取には、安全ラン

者は、書面または口頭による説明を受けた。ラオスの農村

10テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

2. 方法部で は母親の 70% 以上は読み書きができないので、説明

手できなかったため、紙のくじ引き法を用いた選出が考慮に際しては特に注意が払われた。

さ れた。

参加者の情報は匿名とし、機密を保持した。各参加者には識別番号 (ID) を付け、質問 票と血液検体同一の識別番号を記載した。

⿇⿇ 調査参加者の選出

各村から提供されたリストに基づき、参加する 21 例のHBs 抗原の測定結果は、要求があれば母親に知らせた。

小児を NIP のスタッフが無作為に選出した。具体的には

調査チームは、結果を知らせる 前に以下の点を考慮した :1)

1~250 の番号が付けられた 20 × 2cm の細長い長方形の紙

ラオスではウイルス性 B 型肝炎は治療可能ではないこと、

片 21 枚を無作為に封筒から引いて 21 組の母子を選ぶとい

2) Determine® は個別の診断目的に使用されるのではなく、う、紙のくじ引き法を用いて母子のペアを選出 した。各調

疫学的研究のために使用されるキ ットであること、3) 調査

査チームは、250 枚の紙片を入れた封筒を 1 つずつ保有した。

チームが B 型肝炎について詳細に説明しても、地域の信条選定された村に充分な数の小児がいない場合は、調査チーにより HBs 抗原陽性者は村民から差別を受ける可能性があ

ムは郡のセンターへ戻る途中 の最も近い村を選び、居住者ること。

の合同リストを作成して、同じ選出過程を取った。

⿇⿇ 調査の実施

⿇⿇ 監督者と調査員の研修

準備・組織され、遂行・実施さ れた。調査の実施における名、NCLE から 5 名 )、県レベルの 監督者 13 名および現地

各段階について以下にまとめる。

の調査員 48 名を採用した。調査員の職種は、主に検査技師・

B 型肝炎有病率調査は、国、県、郡および村のレベルで⿇⿇ 倫理的承認調査実施にあたり、国レベルの監督者 11 名 (NIP から 6

疫学スタッフであった。国レベルの監督者は、1 つまたは 2つの県を監督し、調査員からの説明 や質問に対応した。

NIP、NCLE および NCGM は、世界保健機関 (WHO) 西太

監督者と調査員に対する 2 日間の研修において、安全ラ

平洋地域事務所およびラオ ス事務所からの支援を得て、調ンセットを用いた指尖穿刺、血液採取と Determine® の結査の理論的根拠、方法論、必要な情報、財政的支援、必要

果の読み方、質問票調査の方法を訓練した。研修には、B

な人的資源について検討した。研究グループは調査プロト

型肝炎に対する国の政策、ID システム、倫理的問題、およコルを作成し、ラオス保健省お よび日本の NCGM の倫理

び機密保持も含まれた。村における無作 為選出を確実にす

委員会に提出した。ラオス保健省の倫理委員会は調査プロるために、紙のくじ引き法の使用が重視された。

トコル を 2011 年 1 月 20 に承認し、NCGM の倫理委員会
は 2011 年 1 月 6 日 (NCGM-950) および 2012 年 1 月 10 日
(NCGM-G-001130-00) に調査を承認した。
⿇⿇ 調査地への公式の要請状と候補者リストの収集

⿇⿇ 材料の準備調査を実施する前に、NIP スタッフは各参加者の ID シス

テムを作成した。識別番号にはクラスターコード ( 県番号 郡番号 - 村名 ) と個人コード [01 から 21 までの 2 桁の数字

村の選定後、保健省の職員は、関連する県、郡および村+C ( 小児の場合 ) または M( 母親の場合 )] が使われた。各へ公式の要請状を送った。事 前に完全な居住者リストは入ID は、質問表用紙に記入され、Determine® 簡易検査でも使テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

11

2. 方法用された。すべての調査物品はクラスターごとにまとめて包装され、調査地へ出発する前に各調査チームに配られた。
⿇⿇ 現地での検査の実施

血液採取と質問票調査ののち、お礼の粗品 ( 菓子の包み、文房具など ) を手渡した。参 加者やその妹・弟がのどに詰まらせる可能性があるので、あめ玉は避けた。監督者と調査 員は、毎日最後に質問票と血液検査結果を検証した。
データ収集は、移動時間を除き 1 月 25 日から 2 月 4 日まで行い、2 週間以内に完了した。デ ータ入力はラオスと日本で行われた。

12

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

3. 結果3. 結果

調査チームは、道路事情の為に到達できなかった一村を965 名の内、17 名の小児 (1.8%) と 28 名の母親 (2.9%) が除いて、選別された 48 村全てを 訪問する事が出来た。訪HBs 抗原陽性であった。下記の表は、サンプリング・デザ

問できなかった一村の代替として、既定の選別基準に従い

インと標本荷重を加味した、母子の HBs 抗原陽性率であ る。

別の村 が選別された。調査は順調に進み、1008 名の小児と3 回目の DPT-HepB ワクチン接種率による階層 ( 高接種率、1008 名の母親の検体とデータを収集 する事が出来た。最

低接種率 ) によって分け た陽性率も下表に示す。

終的な回答率は 100% であった。しかし、43 組の母子は年齢基準に当 てはまらず分析から除外された。43 組の内訳は、4 名の小児が 9 歳以上、30 名が 5 歳未満、5 名の母親が 45
歳以上、4 名の母親が 15 歳未満であった。その結果、965組の母子のデー タが HBs 抗原陽性率の計算に用いられた。

母児の B 型肝炎抗原陽性率 ( 小児 ;5-9 歳、母親 ;15-45 歳 )表 . 全国母児 B 型肝炎抗原陽性

年齢
小児(n=965)母親(n=965)

B 型肝炎抗原陽性

95% C.I.

デザイン効果1.7%

0.8-2.6%

1.1

2.9%

1.7-4.2%

1.3

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

13

3. 結果表 . 3 回目の DPT-HepB 接種率による階層別 HBs 抗原陽性率

年齢
小児、低接種率(n=479)
小児、高接種率(n=486)
母親、低接種率(n=479)母親、高接種率(n=486)

B 型肝炎抗原陽性率

95% C.I.

2.3%

1.0-3.6

1.2%

0.2-2.2

1.9

0.7-3.1

3.7

2.0-5.4

表 . 背景因子による HBs 抗原

因子

内訳
<=19

20-24
母親の年齢

最寄りの保健センターまでの交通手段

85

294

35-39

176

30-34

HBs
抗原陽性

HBs
抗原陰性

1

82

0
7

3

8

9

131

0

127

4

6

243

1

292

7

354

10

3

62

4

3

高地ラオ族

62

2

14

0

242

徒歩

297

バイク

357

トラクター

63

車

0

266

9

自転車

286

HBs
抗原陽性

6

642

中地ラオ族

4

母親

275

低地ラオ族

その他

14

4

25-29

40-45

人種

HBs
抗原陰性

小児

178
14

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

5

0

173

3

632

19

61

3

14

177
14

5
6
0

6
0

3. 結果因子

内訳
0-4

最寄りの保健センター
までの所要時間 ( 分 )

5-14

6

60-480

153

3

152

4

30-59

204

5

205

4

300

7

295

12

182

3

183

2

小学校修了

369

高校修了

73

0

農夫

670

13

664

19

労働者

91

1

87

5

工場勤務

8

0

8

0

63

0

中学校修了

公務員

19
5

87

5

1
0

1

364
72
18
5

85

一般勤務

15

1

16

その他

8

0

8

有り

62
93

1
2

無し

852

15

女児

465

9

男児

479
203

郡病院

103

プライベート診療

11

保健センター

7

4

93

10
1
2

0
3

0
0

3

843

24

201

6

2

100

5

0

10

1

10

0

自宅

561

8

555

14

その他 ( 施設 )

3

0

3

0

森

小児の手術歴の有無

1

11

県病院

分娩場所

268

30

220

商人

小児の性別

3

0

HBs
抗原陽性

5

漁夫

母親の手術歴の有無

271

HBs
抗原陰性

226

大学修了

世帯主の職業

31

HBs
抗原陽性

母親

15-29

小学校修了せず
母親の教育レベル

HBs
抗原陰性

小児

有り

無し

53

22

922

3
0

10

55

0

1

16

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

15

4. 考察と結論

4. 考察と結論

⿇⿇ 考察
1.

調査の実施

血清 B 型肝炎有病率調査が成功裏に終了したのには下記の理由があった。
1)
2)
3)
4)

た。歯ブラシの共有、手術歴、母親の教育レベル、そして、
民族 が、それぞれ独立して、感染状態と関連していたという報告がある [11, 12, 13, 14]。児の B 型肝炎感染状態と有意差のあるリスク因子を検出できなかった理由は明確ではないが、ラオス保健省が調査実施に強力にコミットしてく

恐 らく、陽性例が少なすぎるせいではないかと思われた。

れた。

今回の調査の第一の目的は、B 型肝 炎抗原陽性率を見る為

全ての行政レベルにおいて、コミュニケーション

であり、リスク因子の抽出は、一義的なものではない。また、と協力体制が円滑であった。

HIV 陽性例に関して、B 型肝炎罹患が陽性に関連していると村長をはじめとする地域の重要人物、保健ボランする報告があるが、今回の調査では、予算も限られており、ティアが調査に関与してくれた。

HIV を検索することはできなかった。

2011 年の中部地域におけるパイロット調査を参考にする事が出来、調査チームが非常に よく準備さ

4.

れていた。

世界保健機構 (WHO) 西太平洋地域の目標
WHO の B 型肝炎罹患に関する暫定目標は、2012 年までに 5 歳以上児の罹患率を 2% 未満 にするというものである
2.

母子の HBs 抗原陽性率(WPR/RC56.R8)。B 型肝炎コントロールの評価の為に点推定

調査から得られた一般人口の推定 HBs 抗原陽性率は、小が 使われている。この基準に照らしてみると、ラオスは既児においても、母親においても、近隣諸国およびラオスでに目標に達している事になる [7, 8]。 しかし、ラオスは WHO報告されているよりもかなり低値であった [5, 6, 7, 8]。その原

西太平洋地域でワクチン接種率が最も低い国であるである

因と して、幾つかの理由が考えられた。

ことか ら、予防接種プログラムのみで目標を達成したとは

1) ラオスの人口密度は、近隣諸国と比較して低く、そ考えにくい。以前の報告と比較して母の為人と人との接触の機会が少ない。 それに加え、親の HBs 抗原血清陽性率が比較的低い事から、B 型肝炎予道路・鉄道・航空等の設備が整っておらず、ウイル

防接種プログラム導入前から既 に有病率は低かった事が示スの伝播の機会が少ない。文化や人の行動の違い唆される。それゆえ現行の予防接種政策を単純に続けるだも、低い陽性率に影響を与えていると考えられる。

けで は、最終目標である 5 歳以上児の HBs 抗原陽性率を

2) ラオスから以前発表された報告は、全人口を正確に代表していると云えないものが多か った。例えば、2 つの先行研究 ( 献血者 [9] と入院患者 [10]) では、
都市部における高い罹患 率を示していたが、標本1% 以下に抑えるのは難しいのではな いかと思われる。
⿇⿇ 推奨
1.

が一般人口を代表しているとは考えにくい。

全国予防接種プログラムを評価する為には、HBs 抗原
陽性率調査を繰り返す必要がある。 次回の調査時は、最新の人口データを使用する必要がある。

3.

可能性のある危険因子
今回の調査は、母親の B 型肝炎感染状態以外には、児の感染状態に関する有意差のある危 険因子を同定できなかっ16

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

2.

次回調査時は、調査対象者として、下記を網羅することを推奨する1)

母親 ; 垂直感染の原因となる為4. 考察と結論

2)

父親 ; 児への水平感染の原因となる可能性がある為

3)

社会的弱者 ( 移民、コマーシャル・セックスワー
カー ); 彼らは非登録人口であるが、一般人口よりも高い有病率を示す可能性がある為。データ収集の際にはサンプリン グ法に特別な注意を払う必要がある (oversampling methodology の利用等 )。

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

17

文献

文献

1. Kane MA. (1996) Global status of hepatitis B immunization. Lancet 348: 696.
2. Lee WM. (1997) Hepatitis B virus infection. N Engl J Med 337: 1733–1745.
3. Ol HS, Bjoerkvoll B, Sothy S, Heng YV, Hoel H, et al. (2009) Prevalence of hepatitis B and hepatitis C
virus infections in potential blood donors in rural Cambodia. Southeast Asian J Trop Med Public Health40: 963-971.
4. Hipgrave DB, Van NT, Huong VM, Long HT, Dat DT, et al (2003) Hepatitis B infection in rural Vietnam
and the implications for a national program of infant immunization. Am J Trop Med Hyg 69: 288-294.
5. World Health Organization, Documenting the impact of hepatitis b immunization: best practices for
conducting a serosurvey (WHO/IVB/11.08).
Available: http://whqlibdoc.who.int/hq/2011/WHO_IVB_11.08_eng.pdf
Accessed 12 September 2012
6. Merican I, Guan R, Amarapuka D, Alexander MJ, Chutaputti A, et al. (2000) Chronic hepatitis B virus
infection in Asian countries.
J Gasroenterol Hepatol 15: 1356-1361.
7. Rani M, Yang BP, Nesbit R (2009) Hepatitis B control by 2012 in the WHO Western Pacific Region:
rationale and implications. WHO Bull 87: 707-713.
8. World Health Organization (2011) Progress towards meeting the 2012 hepatitis B control milestone:
WHO Western Pacific Region, 2011. Wkly Epidemiol Rec 86: 180-188.
9. Jutavijittum P, Yousukh A, Samountry B, Samountry K, Ounavong A, et al. (2007) Seroprevalence ofhepatitis B and C virus infections among Lao blood donors. Southeast Asian J Trop Med Public Health38: 674-679.
10. Syhavong B, Rasachack B, Smythe L, Rolain JM, Roque-Afonso AM, et al. (2010) The infective causesof hepatitis and jaundice amongst hospitalised patients in Vientiane, Laos. Trans R Soc Trop Med Hyg
104: 475-483.
11. Soeung SC, Rani M, Huong V, Sarath S, Kimly C, et al (2009) Results from nationwide hepatitis B
serosurvey in Cambodia using simple and rapid laboratory test: implications for national immunization
program. Am J Trop Med Hyg 81: 252-257.
12. Duong TH, Nguyen PH, Henley K, Peters M (2009) Risk factors for hepatitis B infection in rural
Vietnam. Asian Pacific J Cancer Prev 10: 97-102.
13. Ashraf H, Alam NH, Rothermundt C, Brooks A, Bardhan P, et al. (2010) Prevalence and risk factorsof hepatitis B and C virus infections in an impoverished urban community in Dhaka, Bangladesh. BMC
Infect Dis 10: 208.
14. Liang XF, Bi SL, Yang WZ, Wang LD, Cui G, et al (2009) Epidemiological serosurvey of hepatitis B in
China-declining HBV prevalence due to hepatitis B vaccination. Vaccine 27: 6550-6557.

18

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

資料

資料

資料は巻末に収録（英語版に共通）
資料 1.

調査の為に選別された郡と村

資料 2.

質問票

資料 3.

インフォームド・コンセント・フォーム

資料 4.

研修内容

資料 5.

監督者と調査員

資料 6.

掲載論文

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

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20

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

Hepatitis B Prevalence Survey
in Lao PDR

Aknowledgements

Aknowledgements

We gratefully acknowledge the following groups and individuals for their assistancewith this study:
Ministry of Health, Lao PDR		National Immunization Program		

National Center for Laboratory & Epidemiology

National Center for Global Health and Medicine, Japan		

Bureau of International Medical Cooperation		Hepatology Research Center

National Institute of Infectious Diseases, Japan		

Department of Virology II

JICA (Japan International Cooperation Agency) projects
		Capacity Development for Sector-wide Coordination in Health-Phase2 		Strengthening Integrated Maternal, Neonatal and Child Health Services
		

Sustainable Development of Human Resource for Health to Improve 		

Maternal, Neonatal and Child Health Services
World Health Organization
		Regional Office for the Western Pacific
Lao PDR office

22

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDRAcronyms

Acronyms

C.I.

Confidence interval

DPT-HepB 3

Diphtheria, pertussis, tetanus, hepatitis B vaccine the third dose

EPI

Expanded Programme on Immunization

HB

Hepatitis B

HBsAg

Hepatitis B surface antigen

JICA

Japan International Cooperation Agency

MoH

Ministry of Health, Lao PDR

NCGMNational Center for Global Health and Medicine

NCLE

National Center for Laboratory and Epidemiology, MoH

NIPNational immunization Program, Maternal and Child Health, MoH

PPS

Probability proportionate to size

SBA

Skilled birth attendance

VPD

Vaccine preventable diseases

WHO

World Health Organization

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

23

Executive Summary

Executive Summary

To assess current hepatitis B prevalence among

village (cluster), surveyors randomly selected 21 child-general population and the impact of hepatitis B

mother pairs from resident lists. After explanation of

vaccine introduction in Lao PDR, Ministry of Health, Lao

survey purposes, methods, confidentiality policy, and

PDR, and NCGM planned a serology and questionnaireobtaining informed consent, questionnaire and blood

survey. The survey, which covers the whole country,

sampling were conducted. Blood samples were tested

was completed in February 2012. This report

HBsAg using Determine® rapid test.

summarizes the results of the survey.
⿇⿇ Results

⿇⿇ Objectives

A total of 2,016 blood samples (1,008 children

Primary objectives of the survey are

and 1,008 their mothers) were collected and found tosummarized below.

have hepatitis B virus prevalence of 1.7% (95%C.I.=0.8,

1.

To estimate hepatitis B surface antigen sero-

2.6) for children between five to nine years old and 2.9%

prevalence among children(95%C.I.=1.6, 4.2) for their mothers with child bearing

To estimate hepatitis B surface antigen sero-age. Mother’s infection status was positively associatedprevalence among motherswith their children’s HBsAg positivity, while otherTo evaluate the potential risk factors

potential risk factors (mother’s age, ethnicity, time to2.
3.

the nearest health center, level of mother’s education,
⿇⿇ Target ages, areas, and time
Ages

ChildrenFive to nine year-old

Mothers

15 to 45 year-old

Areas

Whole country

Time

January and February, 2012and medical history) were not.
⿇⿇ Discussion and recommendations

This is the first nationwide population-based

hepatitis B sero-prevalence survey in Lao PDR. The
prevalence results of the survey were lower than the

⿇⿇ Survey methodologies

results from surrounding countries. The major reasons

All 143 districts in Lao PDR were stratified intoof differences are unclear. Hepatitis B birth dose andtwo categories; high and low third DPT-hepatitis B

three vaccinations during infancy remain important

immunization coverage reported in 2010. 12 districts

preventive strategies; therefore, careful monitoringfrom each stratum were selected by probability

and repeated evaluation for national immunization

proportionate to size (PPS) sampling, and then two

program are needed.

villages were selected from each district by PPS. In each24

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

1. Introduction

1. Introduction

⿇⿇ Backgroundtargeting prevention for mother to child transmission [7, 8].

More than two billion people have been

The Ministry of Health (MoH), Lao PDR andinfected with hepatitis B (HB) virus worldwide andNational Center for Global Health and Medicine (NCGM)

every year approximately one million people die ofhave agreed that sero-prevalence is investigated. In

HB virus infection, 33 % caused by hepatocellular

January and February 2011, the team focuses on central

carcinoma, and the rest with terminal complications

region of the country as the pilot survey, and the wholeof liver diseases[1, 2]. The Regional Committee for theWorld Health Organization (WHO) Western Pacificadopted the resolution WPR/RC54.R3 in 2003 andresolution WPR/RC56.R8 in 2005, calling for thecountry was covered in January to February 2012.

Table 1. Hepatitis B vaccination activities
in Lao PDR

reduction of chronic hepatitis B infection to less than

2002

2% among 5-year-old children, as an interim milestone

DTP-HepBDTP-HepB as routine
immunization

towards the final regional goal of less than 1%, by 2012.

2004

Birth dose introduced in Capital hospitals

Regional progress in hepatitis B control strategies has

2005

2 southern province hospitals added

resulted in a dramatic decline in hepatitis B infection

2007

8 more provincial hospitals added

among children, and 27 countries and areas are2008

expected to achieve the milestone (WPR/RC61/10).
Lao People’s Democratic Republic (Lao2009

PDR) has initiated its expanded programme on
immunization (EPI) in selected regions in 1984. The

2010

program has scaled up to nationwide in 1994. Hepatitis
B has included in EPI in 2002, and gradually expanded

Remaining provincial and all 123 district
hospitals addedStarted Hepatitis B birth dose home visits
using health center workers

in 50 districts from 9 provinces

Training of skilled birth attendants (SBA)
who can work both in facilities
and attend births at home

(Table 1). Study from neighboring countries, such as

Cambodia, China, Myanmar, Thailand, and Vietnam,
revealed high HB antigen prevalence[3, 4, 5, 6], but there

have been no previous reports of chronic HB virus
infection rates among general population of Lao PDR.
Therefore, population-based sero-prevalence survey

⿇⿇ Survey objectives

Primary objectives of the survey are;1.

prevalence among children
2.

To estimate hepatitis B surface antigen seroprevalence among mothersfor HB is necessary to understand the current situationand to evaluate the progress of immunization policy

To estimate hepatitis B surface antigen sero-3.

To evaluate the potential risk factors

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

25

2. Methods

2. Methods

⿇⿇ Sample size calculation

Considering desired level of confidence

mother pairs were randomly selected using a paperbased lottery system.

measure of 1.96, margin of error of 0.02, expected

Since questionnaire and blood collection time

HBsAg positive rate of 0.05, design effect of 2.0, withis expected as 20 minutes per pair, and transportation

two strata, and response rate of 0.95, we calculated

is often difficult in and among villages, six pairs per day

required sample size of 961, which indicates 961

per survey team were considered to be appropriate.

pairs of mothers and children (1,922 individuals). For

Twenty four survey teams were organized, and eachpractical purposes, 1,008 pairs of children and mothers

team had two surveyors.

(2,016 individuals) are planned to be collected.
⿇⿇ Sampling strategies

⿇⿇ Data collection

Blood samples were taken by trained surveyors

Stratified multi-stage random cluster sampling

using finger-prick method in selected villages. Safety

was used to select pairs of children and mothers withlancet® and glass capillary tube was used for taking

child bearing age.

blood. Approximately 50 micro liter of blood are

Lao PDR comprises Vientiane capital and 16

needed to apply Determine rapid test.

administrative provinces in the country. The country

The survey included a brief questionnaire toincludes 143 districts and more than 10,000 villages

verify the participants’ sex, age and date of birth, place

according to census 2005. We divided all districts intoof residence, sociodenographic characteristics, family

two strata in terms of DPT-HepB3 (diphtheria, pertussis,

history of hepatitis, vaccination history, and potential

tetanus, and hepatitis B third dose) immunization

risk factors of getting hepatitis B.

coverage; high (72 districts >=76%) and low (71 districts

After pre-testing in a non-selected village,<76%). Twelve districts were randomly selected fromtwo-day training session for supervisors and surveyors

each stratum, with applying probability proportionate

was held just before the survey. The national advisors

to size (PPS) sampling as the first stage. For the second

attended the session, too. The lecturers were recruitedstage, two villages were randomly selected from eachfrom NIP and NCLE, MoH, Lao PDR.

district by PPS. In each of 48 villages, household list
was made based on residents list by poverty reduction
program. When poverty reduction program’s list was
not available, EPI list, or relevant residents list was used
when survey team visits selected village. 21 child and26

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

⿇⿇ HBsAg detection using Determine®

HBsAg was assayed using Determine® (Arlier,Japan). Briefly explaining, the blood apply onto thesample pad, followed by the chase liquid. Fifteen

2. Methods

minutes to 24 hours later, the results can be read.

in Lao PDR, 2) Determine® is not used for individual
diagnostic purposes, but for epidemiological research,

⿇⿇ Data entry and analysis

3) HBsAg positive persons may be discriminated byfile sheets. Data was validated by testing double-entry

give detailed explanation about hepatitis B.

All the information was input into the excel

villagers according to local beliefes, even survey teams

checking.
The results were analyzed by STATA ver. 12.0
(Stata Corp., College Station, Tx, USA).

⿇⿇ Survey implementation

The hepatitis B survey was prepared, organized,

executed and implemented at national, provincial,
⿇⿇ Ethical considerations

To minimize risks, each blood sample

district, and village levels. The steps involved in survey
implementation are summarized as follows.

collection used a new, disposable lancet. Supervisorsand surveyors were trained during training session.
Surveyors followed manufacturer instructions and used

⿇⿇ Ethical approval

NIP, NCLE, and NCGM had discussion ofa pair of latex gloves for each child. Immediately after

rationale, methodology, necessary information,use, all lancets and cotton balls were placed in safety

funding, and human resources required for the survey

boxes.

with assistance from WHO (WPRO and Lao PDR) offices.
Before conducting the survey, local authorities

The study group developed the survey protocol and(village leaders and the presidents of local Women’s

submitted to ethical committees in MoH, Lao PDR and

Union) and the parents or guardians of selectedin NCGM, Japan. The ethical committee in MoH, Laochildren received oral and written information. Special

PDR approved the survey protocol in January 20, 2011,attention was paid for this explanation, as more thanand the NCGM ethical committee approved the survey

70% of mothers would be illiterate in rural Lao PDR.

in January 6, 2011 (NCGM-950) and January 10, 2012

Participant information was remained(NCGM-G-001130-00).

anonymous and confidential. Each participant has
identification number, which is common between
questionnaire and blood sample.
The HBsAg results were informed to mothers

⿇⿇ Official request letter to survey sites andcollecting lists of eligible subjects

After selection of villages, the MoH cabinet

on request. Survey teams considered following issues

sent an official letter to the relevant provinces, districts

before giving results; 1) Viral hepatitis is not curable

and villages. Complete lists of the residents were notTechnical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

27

2. Methods

available beforehand, therefore, selection using paper-

national policy against hepatitis B, coding system,

based lottery system was considered.

ethical issues, and confidentiality.To ensure random
selection in villages, using a paper-made lottery

⿇⿇ Survey subjects selection

sysytem was emphasized.

staff randomly selected 21 children for participation.

⿇⿇ Preparing materials

Based on the lists provided by each village, NIP

Child and mother pairs were randomly selected using

Before conducting the survey, NIP staff

a paper-based lottery system in which 21 rectangularprepared the coding system for each participant.

strips of paper, measuring 20 x 2 cm and numbered

Coding included a cluster code (province number-from 1 to 250, were randomly drawn from an envelope

district number-village name) and a personal code (twoto select 21 child and mother pairs. Each survey team

digits ranging from 01 to 21 plus ‘C’ for children andhad one envelope containing 250 strips of paper.

‘M’ for their mothers). Each code was written on the

When a selected village lacked sufficientquestionnaire sheets, and Determine® rapid test. All

number of children, the survey team selected thesurvey materials specific to each cluster were packaged

nearest village on the way back to district center, madetogether with. Each survey team received these

combined list of residents, and followed the same

packages of materials before departing to survey sites.

selection process.
⿇⿇ Training supervisors and surveyors

⿇⿇ Conducting serology in the field

After the blood taking and questionnaire,

The study team recruited 11 national advisorsa small gift was handed (a packet of confectionary,(six from NIP and five from NCLE), 13 provincial

stationery materials, and so on), and hard candy was

supervisors, and 48 surveyors in the field. The

avoided, as participants’ younger sibrings may have

surveyors’ background were mainly laboratory andpossibility of suffocation. At the end of each day, theepidemiology staff. National advisors supervised one

supervisors and surveyors verified the questionnaireor two provinces, and responded to clarifications andand blood test results.

questions from the surveyors.

The data collection was carried out from

Two-day training for both supervisor andJanuary 25th to February 4th excluding transportation

surveyor provided finger-prick using safety lancet,

time, and completed within two weeks. Data input was

blood collection and Determine® result reading,conducted in Lao PDR and in Japan.

and taking questionnaire. The training also included

28

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

3. Results

3. Results

The survey teams successfully visited all 48

age and four were less than 15 years of age. A total of

selected villages except one village, which could not

965 pairs were included for the prevalence calculation.

be approached because of difficult road condition.

Seventeen out of 965 children (1.8%) and 28

An alternative village was chosen according toout of 965 mothers (2.9%) showed positive for HBsAg.

predetermined selection criteria. Data collection was

The table below shows the overall HBsAg prevalence

successfully carried out and sampled 1,008 children

among children and their mothers after taking theand 1,008 their mothers. The overall response rate

sampling design and sampling weight for each

was 100%; however, 43 pairs were excluded from theindividual into account. HBsAg prevalence in each age

analysis due to age ineligibility. That is, four children

gourp by strata (high and low DPT-HepB 3 coverage) is

were over 9 years of age and 30 were less than 5 years

also presented.

of age.Moreover, five mothers were over 45 years of

HBsAg prevalence among children (5 to 9 years old) and their mothers (15 to 45 years old)
Table. National HBsAg prevalence among children and their mothers

Ages
Children(n=965)
Mothers(n=965)

HBsAg prevalence

95% C.I.

Design effect1.7%

0.8-2.6%

1.1

2.9%

1.7-4.2%

1.3

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

29

3. Results

Table. HBsAg prevalence among children and their mothers by DPT-HepB 3 coverage
Ages
Children, low coverage(n=479)Children, high coverage(n=486)

HBsAg positive rate

95% C.I.

2.3%

1.0-3.6

1.2%

0.2-2.2

1.9

0.7-3.1

3.7

2.0-5.4

Mothers, low coverage(n=479)Mothers, high coverage(n=486)

Table . HBsAg distribution by background characteristics
Factors

Value
<=19

20-24

Mother's age

Transportation to thenearest health facility

30

Mothers

HBsAg
negative

HBsAg
positive

HBsAg
negative

HBsAg
positive

85

1

82

3

266

9

4

0

4

25-29

294

7

286

35-39

176

3

173

30-34

40-45

Ethnicity

ChildrenLowland Lao
Midland Lao

Highland Lao

275
131

0

3

4

9

632

19

62

2

61

3

242
297

Bike

357

14

6

7

354

10

3

62

4

0

5

Others14

0

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

5

292

178
63

243

1

Car

Tractor

127

8

642

Walk

Bicycle

6

0

14

177
14

6

0
6

0

3. Results

Factors

Value

health facility(min)HBsAg
positive

HBsAg
negative

HBsAg
positive

5-14

271

3

268

6

30-59

204

5

205

15-29

60-480Mother’s educationleveloccupation

operation
Child's sex

220

11
4

Primary school
not finished

300

7

295

12

Primary school
finished

369

5

364

10

Junior high school
finished

182

3

183

2

High school
finished

73

0

72

1

College or university
finished

19

1

18

2

Farmer

670

13

664

19

Labour

91

1

87

5

Factory employee

8

0

8

0

63

0

Public officer

587

General Employer

15

Others

8

Yes

62

93

0

1

0

8

1

2

15

Female465

9Health center
Private clinic

479

203
103
10

11

House

561

Others(facility)

3

Yes
No

53
22

922

85
16

852

Male

5

1

No

In bushoperation

1

4

District hospitalChild’s surgical

5

30

152

Province hospital

Place of delivery

226

0

3

Merchant

Mother’s surgical

31

153

Fisherman
Family head

Mothers

HBsAg
negative

0-4Time to the nearest

Children

93

0

3
0
0

3

843

24

4

201

6

0

10

0

7

2
0

100
10

5

1

8

555

14

0

3

0

3
0

55

1

16

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

31

4. Disucussion and Recommendations

4. Discussion and Recommendations

⿇⿇ Discussion
1.

country. For example, previous two studies (blood
donors [9] and the hospitalized patients [10]) revealed

Implementation of the survey
HBsAg sero-prevalence survey was successfullyhigh prevalence of hepatitis B in urban areas ofcompleted because of variety of reasons.

Lao PDR, however, the sampled individuals did not1) The MoH, Lao PDR strongly committed to conduct

represent the general population.

the survey.
2) Communication and coordination was well3.

Potential risk factors
The survey revealed that no potential risk

established in all levels of work.
3) Local authorities and health volunteers are wellfactors were significantly associated with the children’s
infection status, with the exception of the mothers’

involved.
4) Survey team was very well prepared, because they

hepatitis B infection status. Previous HBsAg prevalence

learned a lot from the pilot study targeting central

studieys revealed that toothbrush sharing, history ofregion of the country in 2011.

surgery, level of mother’s education, and ethnicity wereindependently associated with hepatitis B infection [11,2.

. The reason why we could not find any potential

HBsAg prevalence among children and their12, 13, 14]mothers in child bearing ages

risk factors having a positive association with hepatitis

The estimated HBsAg prevalence of the general

B infection among children is not clear, but may be

population was much lower in both children anddue to the small number of positive cases. However,

adults than that of previous reports from neighboring

it should be noted that the primary objective of the. There are several

present study was to assess HBsAg prevalence, andcountries and Lao PDR[3, 4, 5, 6]

potential explanations for these observations.

not its risk factors. Additionally, some reports found

1) Lao PDR’s population density is lower thanthat HIV positive individuals are positively associatedthat of surrounding countries, and thus, human contact

with hepatitis B virus infection; however, we did not

is less frequent. Additionally, road, railway, aviation,

investigate HIV due to limited budget.

and related infrastructure are less developed in Lao
PDR, and thus, there is less chance for spread of viruses.
Cultural, and behavioral differences may contribute to
the lower prevalence.

4.

WHO’s regional target
The interim target of the WHO is to reduce

HBsAg prevalence to less than 2% in children aged

2) The majority of the previous surveys did

at least 5 years old by 2012 ( WPR/RC56.R8). The

not adequately represent the entire population of thepoint prevalence is used for monitoring the control

32

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

4. Discussion and Recommendationsof hepatitis B. Following these criteria, Lao PDR had

they are often not registered, and may havealready achieved its goal [7, 8]. However, it is unlikely

higher prevalence of hepatitis B than generalthat Lao PDR had achieved the target through the

population. Special attention should be paid toimmunization program alone because the country

collect data from them, such as oversampling

has the lowest immunization coverage of all countries

methodology.

in the region. Considering the relatively lower HBsAg
seroprevalence among the mothers compare to thosereported in previous studies suggests that the country
has a lower prevalence even before the introduction of
the hepatitis B immunization program. Therefore, thefinal target of reducing HBsAg prevalence to less than
1% in children aged at least 5 years could be difficult
to achieve if the country simply continues its current
immunization policy.
⿇⿇ Recommendations
1.

To evaluate the progress of national immunization
programs, the HBsAg prevalence survey should be
repeated. The next survey should utilize the latest
census data.

2.

When conducting the next survey, we recommendthat the target population include;1) mothers, because they are the source of verticaltransmission2) 2) fathers, because they may be the source ofhorizontal transmission of hepatitis B virus tochildren3) marginalized population, such as floating
immigrants or commercial sex workers, because

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査

33

References

References
1. Kane MA. (1996) Global status of hepatitis B immunization. Lancet 348: 696.
2. Lee WM. (1997) Hepatitis B virus infection. N Engl J Med 337: 1733–1745.
3. Ol HS, Bjoerkvoll B, Sothy S, Heng YV, Hoel H, et al. (2009) Prevalence of hepatitis B andhepatitis C virus infections in potential blood donors in rural Cambodia. Southeast Asian J Trop
Med Public Health 40: 963-971.
4. Hipgrave DB, Van NT, Huong VM, Long HT, Dat DT, et al (2003) Hepatitis B infection in rural
Vietnam and the implications for a national program of infant immunization. Am J Trop Med
Hyg 69: 288-294.
5. World Health Organization, Documenting the impact of hepatitis b immunization: bestpractices for conducting a serosurvey (WHO/IVB/11.08).
Available: http://whqlibdoc.who.int/hq/2011/WHO_IVB_11.08_eng.pdf
Accessed 12 September 2012
6. Merican I, Guan R, Amarapuka D, Alexander MJ, Chutaputti A, et al. (2000) Chronic hepatitis B
virus infection in Asian countries.
J Gasroenterol Hepatol 15: 1356-1361.
7. Rani M, Yang BP, Nesbit R (2009) Hepatitis B control by 2012 in the WHO Western PacificRegion: rationale and implications. WHO Bull 87: 707-713.
8. World Health Organization (2011) Progress towards meeting the 2012 hepatitis B control
milestone: WHO Western Pacific Region, 2011. Wkly Epidemiol Rec 86: 180-188.
9. Jutavijittum P, Yousukh A, Samountry B, Samountry K, Ounavong A, et al. (2007)
Seroprevalence of hepatitis B and C virus infections among Lao blood donors. Southeast AsianJ Trop Med Public Health 38: 674-679.
10. Syhavong B, Rasachack B, Smythe L, Rolain JM, Roque-Afonso AM, et al. (2010) The infective
causes of hepatitis and jaundice amongst hospitalised patients in Vientiane, Laos. Trans R Soc
Trop Med Hyg 104: 475-483.
11. Soeung SC, Rani M, Huong V, Sarath S, Kimly C, et al (2009) Results from nationwide hepatitis
B serosurvey in Cambodia using simple and rapid laboratory test: implications for national
immunization program. Am J Trop Med Hyg 81: 252-257.
12. Duong TH, Nguyen PH, Henley K, Peters M (2009) Risk factors for hepatitis B infection in rural
Vietnam. Asian Pacific J Cancer Prev 10: 97-102.
13. Ashraf H, Alam NH, Rothermundt C, Brooks A, Bardhan P, et al. (2010) Prevalence and risk
factors of hepatitis B and C virus infections in an impoverished urban community in Dhaka,Bangladesh. BMC Infect Dis 10: 208.
14. Liang XF, Bi SL, Yang WZ, Wang LD, Cui G, et al (2009) Epidemiological serosurvey of hepatitis
B in China-declining HBV prevalence due to hepatitis B vaccination. Vaccine 27: 6550-6557.

34

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

資料
Annexes

資 料 1: 調査の為に選別された郡と村
資 料 2: 質問票
資 料 3: インフォームド・コンセント・フォーム
資 料 4: 研修内容
資 料 5: 監督者と調査員
資 料 6: 掲載論文
Annex 1: Selected districts and villages
Annex 2: Questionnaire
Annex 3: Informed Consent form
Annex 4: Training agenda
Annex 5: Supervisors and surveyors
Annex 6: Publication

資料 1: 調査のために選別された郡と村 / Annex 1: Selected Districts and villages for the survey

Selected Districts and villages- Selected districts and villages

Xay:• Nalao• NamkoudHouixay:

Viengthong:• Danthin• Manth• Saychalurn• Houaisou

Xiengkhor:• Nahuea• Hub

Phaoudom:• Hartli• Homesook

Hongsa:Pek:• Naphoung• Phonhthong• Namsib• Phonhsavanhsay

Luangprabang:• Khouaty 1

Atsapangtong:• Yang

Kenethao:• Chomkeo• Pakkham

Xanakhame:

Sikhottabong:• Siphoun• Nasack

Toulakhom:• Xaysomboun• Kangmeuang• Vanghueang• Nonkeo• Sithannuea• Nalaydong

Nong:

Xaythany:• Tayong• Saen-Koh• Phoukham• Tha dean deng nuea

Chanthabouly:• Phontong chommany nuea

• Hatsadee tay

Champhone:• Laosouliya• Donekhagnungna• Luck 35

Xonbuly:

Saravane:• Houaimuang• Baengxekong• Tangvaitay• Nongbouagnai

Phonthong:• Phonkeo

Bachieng:• PongSukhuma:• Hae• Nong phan vong

36

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

Toumlane:• Nahonggnai

Khong:• Bounnoy• Dedvanttok• Nongboknoy• Huoaisae

資料 2: 質問票 / Annex 2 : Questionnaire

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査37

資料 2: 質問票 / Annex 2 : Questionnaire

38

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

資料 2: 質問票 / Annex 2 : Questionnaire

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査39

資料 2: 質問票 / Annex 2 : Questionnaire

40

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

資料 2: 質問票 / Annex 2 : Questionnaire

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査41

資料 2: 質問票 / Annex 2 : Questionnaire

42

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

資料 3: インフォームド・コンセント・フォーム / Annex 3 : Informed Concent form

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査43

資料 3: インフォームド・コンセント・フォーム / Annex 3 : Informed Consent form

44

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

資料 3: インフォームド・コンセント・フォーム / Annex 3 : Informed Concent form

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査45

資料 4: 研修内容 / Annex 4 : Training agenda

Training agenda 2012
23rd Jan
08:00

Registration

08:30

Opening

Dr. Phengta, Dr. Hachiya

09:00-10:00

Purpose of WS

Dr. Anonh

10:00-10:15

Break

10:15-10:30

Study design

Dr. Hachiya, Dr. Anonh

10:30-12:00

Household listing

Dr. Tongchanh(Lecture and practice)
12:00-13:30

Lunch

13:30-15:00

Questionnaire

Dr. Tongchanh(Lecture and practice)
15:00-15:15

Break

15:15-16:15

TOR of surveyors, supervisors, advisors

16:15-16:30

Q&A

Dr. Phengta, Dr. Anonh

24th Jan
08:30-10:30

Blood sampling

Dr. Tongchanh(Lecture and practice)
10:30-10:40

Break

10:40-11:20

Ethical consideration

Dr Anonh

11:20-12:00

Writing the identification numbers

Dr Anonh(Items; questionnaires)
Reporting using SMS and collecting data

Dr Anonh(Lecture and practice)46

12:00-13:00

Financial and logistic issues

13:00

Closing

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

Dr Phengta, Dr Hachiya資料 5: 監督者と調査員 / Annex 5: Supervisors and surveyors

Number

Name

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56

Ms. Vilaphenh Yengmala
Ms. Kham Taune Kouangvanh
Ms. Bounteing Phommavongsa
Mr. Khamsen Phanouvong
Ms. Sengphet Douangsavay
Pengthong Keomahavong
Ms. Lamthong Pamisay
Mr. Houmpheng Thionkeo
PhonepaseuthThongkham Keobouachanh
Ms. Ketchanh Sysavath
Mr. Khamsim
Ms. Souchitta Heuanmisavath
Mr. Bounleune SitdavanhThongphet
Mr. Phanthaly
Ms. Somdy
Ms. Manisouk Phonpadid
Mr. Aiew Thong
Mr. Phanthong Souvannaly
Mr. Bountienne Souphanthong
Ms. Pom Keohomdy
Mr. Khamphanh Keobounta
Ms. Siamphone Vannithorn
Mr. Touk Souvannasing
Dr. Souvanxay Phetthanaxay
Mr. Thongdy Phouangkeo
Mr. Songkharm Masouvanh
Ms. Somsanith Ounthavong
Mr. Thoumphone Bounlieng
Ms. Khamla Yoysaykhem
Mr. Khounlavanh Keolakotphosy
Ms. Manisong Vikayhong
Ms. Bounvang Phinith
Mr. Sisouphan Davanh
Ms. Bouasone Vilailoth
Ms. Orlathay Phongphoun
Mr. Inpeng Nanthanontry
Mr. Salika Kietsatit
Mr. Khampha Senviseth
Ms. Phoukhao
Ms. Sypaseulk
Ms. Bounthan Souvannavong
Ms. Bounta Xayavong
Dr. Laycham Chamsina
Dr. Viengsayphone Mylounsa
Ms. Souphalack Keoounheuane
Dad Samkham
Mr. Sengdavy Syonesa
Mr. Vilayvong
Ms. Viengsavanh Phimpiseng
Mr. Khamla Souphavady
Mr. Visay Xounthay
Ms. Khaysy Vonvilay
Ms. Phimmasone Duangvilay
Mr. Maly Thoubthong

Roles during Survey
Vientiane C Supervisor
Vientiane C Surveyor
Vientiane C Surveyor
Vientiane C Surveyor
Vientiane C Surveyor
Vientiane C Surveyor
Vientiane C Surveyor
Oudomxay Supervisor
Oudomxay Surveyor
Oudomxay Surveyor
Bokeo Supervisor
Bokeo Surveyor
Bokeo Surveyor
Bokeo Surveyor
Bokeo Surveyor
Luangprabang Supervisor
Luangprabang Surveyor
Luangprabang Surveyor
Huaphan Supervisor
Huaphan Surveyor
Huaphan Surveyor
Huaphan Surveyor
Huaphan Surveyor
Xayabouly Supervisor
Xayabouly Surveyor
Xayabouly Surveyor
Xayabouly Surveyor
Xayabouly Surveyor
Xiengkuang Supervisor
Xiengkuang Surveyor
Xiengkuang Surveyor
Vientiane P Supervisor
Vientiane P Surveyor
Vientiane P Surveyor
Vientiane P Surveyor
Vientiane P Surveyor
Savannakhet Supervisor
Savannakhet Surveyor
Savannakhet Surveyor
Savannakhet Surveyor
Savannakhet Surveyor
Savannakhet Surveyor
Savannakhet Surveyor
Savannakhet Surveyor
Savannakhet Surveyor
Saravane Supervisor
Saravane Surveyor
Saravane Surveyor
Saravane Surveyor
Saravane Surveyor
Champasak Supervisor
Champasak Surveyor
Champasak Surveyor
Champasak Surveyor
Champasak Surveyor
Champasak Surveyor

Position
Technical Officer
Epidemiology
Deputy Chief of Labo.
Epidemiology
Laboratory
Epidemiology
Laboratory
Epidemiology
Epidemiology
Laboratory
Epidemiology
Epidemiology
Laboratory
Epidemiology
Laboratory
Epidemiology
Epidemiology
Laboratory
Surveillance staff
Surveillance staff
Epidemiology
Laboratory
Laboratory
Epidemiology
Laboratory
Epidemiology
Laboratory
Epidemiology
Surveillance staff
Surveillance staff
Laboratory
Epidemiology
Epidemiology
Laboratory
Epidemiology
Laboratory
Epidemiology
Epidemiology
Laboratory
Laboratory
Epidemiology
Laboratory
Epidemiology
Laboratory
Epidemiology
Epidemiology
Laboratory
Epidemiology
Epidemiology
Laboratory
Epidemiology
Epidemiology
Epidemiology
Epidemiology
Laboratory
Epidemiology

テクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査47

資料 5: 監督者と調査員 / Annex 5: Supervisors and surveyors

Number
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78

48

Name

Roles during Survey

Position

Ms. Saovalith SimeuangChampasak Surveyor
Laboratory
Ms. Phaiboun Chansavad
Champasak Surveyor
Laboratory
Ms. Manivone BouathongChampasak Surveyor
Laboratory
Dr. Darouny Phonekeo
Vientiane C National Advisor NCLE staff
Dr. Anonh
Oudomxay National Advisor
EPI Director
Dr. Khansay Sengsaya
Bokeo National Advisor
NCLE staff
Dr. Virasack Somoulay
Luangprabang National Advisor NCLE staff
Dr. Khamphet Louanglat
Hoaphan National Advisor
EPI staff
Dr. Khongxay
Xayabuly National Advisor
EPI staff
Dr. Souphatsone Houathougkham Xiengkuang National Advisor NCLE staff
Dr. Dasavanh Manivong
Vientiane P National Advisor MCH staff
Dr. Chansay Pathammavong
Savannakhet National Advisor EPI staff
Dr. Chanthavy Soulaphy
Saravane National Advisor
NCLE staff
Dr. Somvang BouphaphanhChampasak National Advisor EPI staff
Dr. Phengta Vongphrachanh
Lecturer
NCLE Director
Dr. Bounthanom Sengkeopraseuth Lecturer
NCLE staff
Mr. Khamphet
Driver
EPI staff
Mr. Bouavanh Boualivanh
Accounting
EPI staff
Ms. Bounsalong Xayasinh
Accounting
EPI staff
Ms. Bounphet Sisoumang
Accounting
EPI staff
Ms. Phailamphanh Manivong
Vientiane P National Advisor Epidemiology
Ms. Vilaphanh Yengmala
Savannakhet National Advisor Surveillance staff

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

資料 6: 掲載論文 / Annex 6: Publication

Chronic Hepatitis B Prevalence among Children andMothers: Results from a Nationwide, Population-Based
Survey in Lao People’s Democratic Republic
Anonh Xeuatvongsa1, Kenichi Komada2, Tomomi Kitamura2, Phengta Vongphrachanh3,
Chansay Pathammavong1, Kongxay Phounphenghak1, Thongchanh Sisouk3, Darouny Phonekeo3,
Bounthanom Sengkeopaseuth3, Vilasak Som-Oulay3, Koji Ishii4, Takaji Wakita4, Masaya Sugiyama5,Masahiko Hachiya2*
1 National Immunization Program, Ministry of Health, Lao PDR, Simeuang Road, Vientiane, Lao PDR, 2 Bureau of International Cooperation, National Center for Global
Health and Medicine, Shinjuku, Tokyo, Japan, 3 National Center for Laboratory and Epidemiology, Ministry of Health, Lao PDR, Simeuang Road, Vientiane, Lao PDR,
4 Department of Virology II, National Institute of Infectious Diseases, Musashi-murayama, Tokyo, Japan, 5 Hepatology Research Center, National Center for Global Healthand Medicine, Ichikawa, Chiba, Japan

Abstract
Background: Hepatitis B is regarded as a serious public health issue in Lao People’s Democratic Republic (Lao PDR), a
Southeast Asian country. However, disease epidemiology among the general population is not well known, and thus anationwide cross-sectional survey for hepatitis B surface antigen (HBsAg) prevalence in children and their mothers was
conducted.
Methods and findings: We applied three-stage cluster sampling using probability proportionate to size. After randomly
selecting child (5 to 9 years old) and mother (15 to 45 years old) pairs from the selected villages, questionnaires and HBsAg
rapid tests were conducted. Data from 965 child and mother pairs were analyzed. Multivariate logistic regression analyses
were used to investigate the independent association of individual background characteristics for the odds of being HBsAg
positive. In total, 17 children and 27 mothers were HBsAg positive. HBsAg prevalence was estimated to be 1.7% (95%
confidence interval: 0.8%-2.6%) in children, and 2.9% (95% confidence interval: 1.7%–4.2%) in their mothers after taking
sampling design and weight of each sample into account. Mother’s infection status was positively associated with HBsAg
positivity in children (p,0.001), whereas other potential risk factors, such as ethnicity, proximity to health centers, andhistory of surgery, were not. There were no significant associations between mother’s HBsAg status and history of surgery,and other sociodemographic factors.
Conclusions: Despite the slow implementation of the hepatitis B vaccination program, HBsAg prevalence among children
and their mothers was not high in Lao PDR compared to reports from neighboring countries. The reasons for the differencesin prevalence among these countries are unclear. We recommend that prevalence surveys be conducted in populations
born before and after the implementation of a hepatitis B vaccination program to better understand the epidemiology ofhepatitis B.
Citation: Xeuatvongsa A, Komada K, Kitamura T, Vongphrachanh P, Pathammavong C, et al. (2014) Chronic Hepatitis B Prevalence among Children and Mothers:
Results from a Nationwide, Population-Based Survey in Lao People’s Democratic Republic. PLoS ONE 9(2): e88829. doi:10.1371/journal.pone.0088829
Editor: Pierre Roques, CEA, France
Received October 28, 2013; Accepted January 13, 2014; Published February 28, 2014
Copyright:  2014 Xeuatvongsa et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study was supported by The Grant for Nationa Center for Global Health and Medicine (25-8). The funders had no role in study design, datacollection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: m-hachiya@it.ncgm.go.jp

agent to humans by the International Agency for Research on
Cancer [5].
The prevalence of hepatitis B differs throughout the world.
Southeast Asian countries have been estimated to have a chronic
HBV infection rate of more than 8% before the introduction ofhepatitis B vaccination [6]. The Western Pacific region of theWorld Health Organization (WHO), to which most of theSoutheast Asian countries belong, is assumed to have a highprevalence of hepatitis B [7]. Specifically, the prevalence isestimated to be 9% to 12% among women of childbearing age [8]and 8% to 10% among children in pre-vaccine era [9]. The WHO

IntroductionMore than two billion people have been infected with hepatitis
B worldwide, and among these individuals, more than 350 million
suffer from chronic hepatitis B virus (HBV) infection [1,2,3].
Infection with HBV results in 600,000 to 1.2 million deaths per
year due to chronic hepatitis, cirrhosis, and hepatocellular
carcinoma [2,4]. HBV is responsible for 60% to 80% of theworld’s hepatocellular carcinoma cases, one of the major threecauses of death in Africa, Asia, and the Pacific Rim, andaccordingly, has been categorized as a Group 1 carcinogenic

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Hepatitis B Prevalence in Child and Mother Pairs

estimates that the region has 28% of the global population, while itaccounts for almost half of all chronic hepatitis B infections
worldwide [10].
Hepatitis B vaccination, especially within 24 hours afterchildbirth, is considered the most effective and efficient preventive
measure against hepatitis B infection [3,11]. Based on theseassumptions, the WHO set goals to lower the prevalence ofchronic hepatitis B among children over 5 years of age to 2% by2012 and 1% by 2017. To achieve these goals, the WHO plans toincrease immunization coverage to 65% for the birth dose and
80% for the third dose of the hepatitis B vaccine [7].
Lao People’s Democratic Republic (Lao PDR) is a Southeast
Asian country, located in the center of the Indochina peninsula.
The country is landlocked and surrounded by China, Vietnam,
Cambodia, Thailand, and Myanmar. The neighboring countries
report relatively high hepatitis B prevalence compared to otherparts of the world. For example, a survey from two provinces in
Cambodia reported a hepatitis B surface antigen (HBsAg)
prevalence of 7.7% (95% CI: 6.2%–9.3%) among healthy
volunteer adults [12]. Another population-based survey in aprovince in rural Vietnam found that 18.8% (95% CI: 15.7%–
21.9%) of adults and 12.5% (95% CI: 9.7%–15.3%) of infants
were HBsAg positive at the time of the survey [13]. Thus, Lao
PDR has been regarded as one of the hyperendemic countries forhepatitis B for quite some time and is ranked as a priority country
by the WHO [7,9] despite a lack of data on the prevalence in a
representative population. Pre-vaccine era prevalence was estimated as 11.8% [4], 8–10% [9], or 8% or more [6] for Lao PDR
and Indochina countries. In response to this situation, Lao PDR
has implemented the hepatitis B vaccine into the routine
immunization program since 2002 (at 6, 10, and 14 weeks after
birth), as well as birth dosing since 2004. The birth dosing was
initiated at referral hospitals in the capital city, and then gradually
expanded into rural hospitals (2006), and eventually homedeliveries (2010). However, since then, no direct investigation
has been conducted, and thus a nationwide survey is warranted[7,9]. The routine immunization coverage is reported as 56% for
BCG, 50% for the third DPT, 50% for the third hepatitis B, 40%
for measles, and 46% for oral polio vaccine in 2007, when aproportion of target children were born [14].
The primary objective of the present study was to estimate thechronic HBV infection rates by measuring the seroprevalence of
HBsAg among children aged 5 to 9 years, and their mothers aged
15 to 45 years.

mothers were illiterate. The respondents’ names were not recordedon the questionnaire sheets.

Study population
The target population was children aged 5 to 9 years (date ofbirth: January 2, 2002 to January 1, 2007) and their mothers aged
15 to 45 years (date of birth: January 2, 1966 to January 1, 1997)
living in the selected cluster at the time of the survey. The reasonsfor this selection criteria are: 1) the national and regional hepatitis
control policy target is to reduce chronic hepatitis B prevalence
among children aged 5 years or older [7]; 2) Lao PDR does nothave reliable HBsAg prevalence data among healthy adults, andmothers of childbearing age are considered the major source ofhepatitis B infection for children; and 3) our pilot survey revealed
that between 20 and 25 mother and child pairs can be practicallysampled from each village.

Calculation of sample size
The equation used to calculate the required sample size is asfollows [15,16]:
n~Z2 |p(1{p)DEFF |2 ðd 2 |RRÞwhere n = sample size
Z = significance level for 95% confidencep = expected prevalence
DEFF = design effectd = precision
RR = response rate
The sample size (n) of 961 was calculated on the basis of an
expected HBsAg seroprevalence (p) of 5%, a 5% level ofsignificance (Z), precision (d) of 62.0%, design effect (DEFF) of
2.0, two strata, and response rate (RR) of 95%. For fieldpracticability, we requested 24 survey teams to sample 21 childand mother pairs from each cluster, with the aim of gathering
1,008 pairs in total.

Survey design and sampling
The survey applied a stratified three-stage random cluster
sampling design, a type of probability sampling recommended by
the WHO [15,17]. The survey was carried out by 24 survey teams(two members per team). Team members were recruited from thesame districts that were under investigation to implement thesurvey more smoothly. The survey teams consisted of epidemiology, surveillance, or laboratory staff. The survey teams weresupervised by 11 national personnel (six from the National
Immunization Program and five from the National Center for
Laboratory and Epidemiology, Ministry of Health) as well as 13
provincial officers.
For stratified multistage cluster sampling, immunization coverage by district and population data were obtained from the
National Immunization Program, the Ministry of Health, and theDepartment of Statistics, Lao PDR. For post-survey weightadjustment, the survey teams obtained the latest population datafrom village leaders or health volunteers.
All 143 districts in Lao PDR were stratified into two strata, one
having high (more than 76%) and the other having low (76% orless) immunization coverage for the third diphtheria, pertussis,
tetanus, and hepatitis B (DPT-HepB)vaccines as reported in 2010.
For the first stage, we selected 12 districts from each stratum using
probability proportionate to size (PPS) sampling based on the
population census of 2005. For the second stage, we selected twovillages from each selected district by PPS sampling, and 48

Methods
Ethical considerations
The survey protocol was reviewed and approved by the EthicalCommittee of the Ministry of Health, Lao PDR, and theinstitutional review board of the National Center for Global
Health and Medicine, Japan (NCGM-G-001130-00). Access toselected households was granted by the Ministry of Health, andthe provincial and district government authorities.
After obtaining approval to conduct the survey from local
authorities, surveyors explained the purpose of the survey to village
leaders, selected participants, and their caregivers, assured themthat all information would be strictly confidential and that nonames would be gathered, and that there would be no benefit or
penalties for agreeing or refusing to participate. Written informed
consent was obtained from each mother on behalf of her child foreach pair. Written informed consent was obtained from legal
representatives (next of kin, caregivers, or guardians) when

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Hepatitis B Prevalence in Child and Mother Pairs

NJ, USA) and glass capillary tube, and the blood was applied onto
the sample pad of the rapid test kit. After applying the chasebuffer, surveyors assessed the results after at least 15 minutes, but
no longer than 24 hours. When no control bar appeared after 15
minutes, the test results were considered invalid, and the test was
repeated. Blood spots were collected onto filter paper for further
testing. A 2-day training session was organized for surveyors andsupervisors on the use of the rapid test and the completion of thequestionnaire. To ensure the safety of the blood collection
procedure, surveyors always used a new pair of latex gloves.
Surveyors were instructed to place all capillary tubes and lancets
into safety boxes immediately after use.

villages were randomly sampled in total. In the instances in which
the selected village lacked a sufficient number of children or thesurvey team could not approach the selected village due to safety
or security reasons, the nearest village on the way back to the
district center was selected. For each selected village, surveyors
obtained a list of households, including age and sex, primarily
from the poverty reduction program data with the assistance of thevillage leader, women’s union, and/or healthcare volunteer. Fromthese lists, 21 mothers aged 15 to 45 years old with children aged 5
to 9 years were randomly selected using a paper-based lottery
system. When a mother had multiple children aged 5 to 9 years
old, the youngest child was chosen for the survey. Special attention
was paid to ensure that the child’s biological mother was surveyed,
as adoption is common in rural Lao PDR.
The survey was carried out from January 25th to February 4th,
2012. Each survey team successfully approached their assigned
villages, with the exception of one village, which could not be
visited because of road difficulties. An alternative village waschosen according to the predetermined selection criteria. In total,
1,008 children and 1,008 mothers were sampled. The overall
response rate for HBsAg was 100%; however, 43 pairs were
excluded from the analysis due to age ineligibility. That is, one
child was over 9 years of age and 33 were less than 5 years of age.
Furthermore, three mothers were over 45 years of age and six
were less than 15 years of age. This happened as 43 mothers
confused calendar age with traditional age. In rural areas,
newborns start at one year old and a year is added to their age
for each passing of a Lunar New Year. The surveyors asked
participants for their age in years and their date of birth, andchecked that they matched. A total of 965 pairs were included foranalysis.

Data entry and statistical analysis
All of the completed questionnaires were brought to acentralized location and the data were entered into a Microsoft
Excel 2007 spreadsheet. Data were double-entered and crosschecked. Logistic regression tests and odds ratios were used to
examine the relationship between the independent variables and
HBsAg results. Multivariate logistic regression was used toinvestigate the independent association of different household
and individual characteristics with the odds of being HBsAg
positive. All estimates and standard errors were calculated bytaking the multistage clustered sampling design and the weight ofeach sample into account to give representative, unbiased results.
A p value ,0.05 was considered statistically significant.
In our regression analyses, we adjusted for potential confounders by using the following variables: third DPT-HepB immunization coverage at the location of current residence, mother’s age,
ethnic group, mother’s education level, family head’s occupation,and mother’s HBsAg status. For multivariate logistic regression
analyses, multicollinearity was tested by calculating the varianceinflation factors for each independent variable, and a value ofmore than 10 was considered as having multicollinearity.
All statistical analyses were carried out using STATA version 12(Stata Corp., College Station, TX). Means and proportions were
calculated using STATA’s ‘svy’ function, with each sample
weighted according to estimated population size.

Questionnaires
A brief face-to-face questionnaire was administered to thesampled mother. The questionnaire consisted of 25 questions infour domains of inquiry: sociodemographic background of thefamily (i.e., ethnicity, family head’s occupation, and mother’s
education level), family history of liver diseases, including mother,demographic characteristics of the child (i.e., age, sex, and place ofbirth), and immunization records. Additionally, questions wereasked regarding exposure to potential risk factors for acquiring
hepatitis B infection (e.g., history of blood transfusion, surgicaloperation, and sharing of toothbrush). The questionnaire wasdeveloped in English, translated into Lao, back-translated into
English, and then compared and revised by bilingual staff
members. A small pilot test was conducted prior to the datacollection.

Results
Socioeconomic backgrounds
The baseline characteristics of the 965 mothers and theirchildren are summarized in Table 1. The mean age of the mothers
was 29.1 years (95% CI: 26.2–33.1), and the mean age of thechildren was 5.8 years (95% CI: 5.4–6.3). Of the sampled children,
474 (49.4%) were male and 486 (50.6%) were female (five were
unknown).

Testing for HBsAg

HBsAg prevalence among the general population

We used a simple and rapid test (Alere Determine HBsAg test
card; Alere Medical Co. Ltd., Chiba, Japan) rather than the
traditional ELISA test, as it was better suited to use in the field[14]. The sensitivity and specificity of the test were reported ashigh in two Asian countries [18,19]. In Vietnam, the Determine
HBsAg test validity was measured based on comparison with
HBsAg EIA. Results were 100% in both sensitivity and specificity
in 328 samples [18]. In China, the Determine HBsAg performance was evaluated in comparison with HBsAg EIA for 671
samples. The sensitivity was reported to be 98.9% and specificity
100% [19]. The Determine HBsAg examination kit is one of themost reliable point-of-care HBsAg tests, and is recommended by
the WHO [15]. HBsAg testing was performed according to the
manufacturer’s instructions. Blood was collected from a finger
prick using a safety lancet (BD Safety Lancet, Becton Dickinson,
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Of the 965 pairs included in the study, 17 children and 27
mothers were positive for HBsAg. Six child and mother pairs were
HBsAg positive. The estimated prevalence was 1.7% for children(95% CI: 0.8%–2.6%) and 2.9% for mothers (95% CI: 1.7%–
4.2%) after taking the sampling design and weight of each sample
into account. HBsAg prevalence did not change significantly
between DPT-HepB3 high and low coverage districts in bothchildren and mothers (Table 2).

Potential risk factors
To determine whether background characteristics affect HBsAg
status, we conducted multivariate logistic regression analysis inchildren and their mothers. In children, the mother’s HBsAg status
was positively associated with hepatitis B infection (Table 3),
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Hepatitis B Prevalence in Child and Mother Pairs

Table 1. HBsAg prevalence among children (5 to 9 years old) and mothers (15 to 45 years old) in Lao PDR by selected backgroundcharacteristics.

Mothers’ age(n = 965)

Ethnicity (n = 963)

1

Transportation (n = 939)

2Time (n = 901)

3

Education (n = 962)

4

Occupation (n = 963)n%Children’s
HBsAg (+)%

Mothers’
HBsAg (+)

%

15–19

4

0.41

0

0.00

20–24

85

8.80

1

1.18

0.00–3.52

0

0.00

3

25–29

294

30.47

7

2.38

3.53

0.00–7.53

0.63–4.13

8

2.72

30–34

275

28.50

6

0.85–4.59

2.18

0.44–3.92

9

3.27

35–39

176

18.24

1.16–5.39

3

1.70

0.00–3.64

3

1.70

40–45

131

0.00–3.64

13.58

0

0.00

4

3.05

Low land Lao

0.07–6.04

651

67.60

9

1.38

0.48–2.28

19

2.92

1.62–4.22

Mid land Lao

248

25.75

6

2.42

0.49–4.34

5

2.02

0.25–3.78

High land Lao

64

6.65

2

3.13

0.00–7.51

3

4.69

0.00–10.01

on foot

298

31.74

1

0.34

0.00–1.00

6

2.01

0.41–3.62

bicycle

14

1.49

0

0.00

0

0.00

motor bike

364

38.76

7

1.92

0.51–3.34

10

2.75

1.06–4.43

car

183

19.49

5

2.73

0.35–5.12

6

3.28

0.67–5.88

hand tractor

66

7.03

3

4.55

0.00–9.71

4

6.06

0.15–11.97

other

14

1.49

0

0.00

0

0.00

95% CI, 5 minutes

31

3.44

0

0.00

1

3.23

0.00–9.81

5 to 15 minutes

274

30.41

3

1.09

0.15–2.33

6

2.19

0.45–3.93

15 to 30 minutes

231

25.64

5

2.16

0.27–4.06

11

4.76

2.00–7.53

30 to 60 minutes

209

23.20

5

2.39

0.30–4.48

4

1.91

0.04–3.79. 60 minutes

156

17.31

3

1.56

0.00–4.68

42.56

0.06–5.07

did not finish primaryschool

307

31.91

7

2.28

0.60–3.96

12

3.91

1.73–6.09

primary school

374

38.88

5

1.34

0.17–2.51

10

2.67

1.03–4.32

junior high

185

19.23

3

1.62

0.00–3.46

2

1.08

0.00–2.59

high school

73

7.59

0

0.00

1

1.37

0.00–4.10

college/univ

20

2.08

1

5.00

0.00–15.47

2

10.00

0.00–24.41

other or unknown

3

0.31

1

33.33

0.00–100.00

0

0.00

0.88–2.93

19

2.78

0

0.00

farmer

683

70.92

13

1.90

fisherman

5

0.52

0

0.00

laborer

92

9.55

1

1.09

0.00–3.25

55.43

0.71–10.16

public officer

88

9.14

1

1.14

0.00–3.40

36.25

1.70–10.80

factory employee

8

0.83

0

0.00

0

0.00

general employee

16

1.66

1

6.25

0.00–19.57

0

0.00

merchant

63

6.54

1

1.59

0.00–4.76

00.00

others

8

0.83

0

0.00

0

0.00

Mother’s surgery(n = 962)

yes

95

9.88

2

2.11

0.00–5.05

3

3.16

0.00–6.74

no

867

90.12

15

1.73

0.86–2.60

24

2.77

1.67–3.86

Child’s sex (n = 960)

male

474

49.38

9

1.89

0.67–3.13

Place of delivery(n = 961)

Child’s surgery (n = 960)

1.55–4.02

female

486

50.63

7

1.44

0.38–2.50

province hospital

207

21.54

4

1.93

0.04–3.82

6

2.90

0.59–5.20

district hospital

105

10.93

2

1.90

0.00–4.56

5

4.76

0.62–8.90

health center

10

1.04

0

0.00

0

0.00

private clinic

11

1.14

0

0.00

1

9.09

0.00–29.35

at home

569

59.21

8

1.41

0.44–2.38

14

2.46

1.18–3.74

in the forest

56

5.83

3

5.36

0.00–11.44

1

1.79

0.00–5.36

other health facility

3

0.32

0

0.00

0

0.00

yes

22

2.29

0

0.00

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95% CI

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Hepatitis B Prevalence in Child and Mother Pairs

Table 1. Cont.

no1

Transportation to the nearest health facility,
doi:10.1371/journal.pone.0088829.t001

2

n

%

Children’s
HBsAg (+)%

95% CI

938

97.71

16

1.71

0.88–2.54

Time to the nearest health facility,3

whereas the other potential risk factors were not associatedaccording to the adjusted odds ratio. We did not obtain
information regarding the type of delivery, and we did not findsignificant differences in HBsAg prevalence associated withdelivery settings. No independent factor was positively associatedwith HBsAg positivity in mothers, according to the adjusted odds
ratio (Table 4).

Mothers’
HBsAg (+)%

95% CI

Mothers’ completed education, 4 Family head’s occupation.

the study design is a cross sectional survey, it is difficult to explain
the reasons for the unexpectedly low prevalence. There are several
potential explanations for this observation. The survey methodology used was very different from that used for blood donors,
patients, and migrant workers. We used probability sampling andthus the results are representative of the whole population,
whereas studies of blood donors, hospitalized patients, andmigrant workers used non-probability sampling and therefore
the results are restricted to these populations. The primaryobjective of our survey was to estimate HBsAg prevalence among
the general population, so probability sampling was the mostappropriate choice. Demographic conditions among the sampled
population are determined by survey methodology, and therefore
the results showed discrepancy. The WHO strongly recommends
probability sampling for hepatitis B prevalence survey [7,15,17].
Although Lao PDR has the lowest population density of the
Indochina peninsula countries [25], the precise effects on hepatitis
B prevalence of the reduced frequency of human to humancontact due to the country’s relatively low population density andless developed infrastructure remain unclear.
The number of HBsAg positives varied from 0 to 4 per cluster.
Since the sampling design of the survey aimed to estimate theprevalence in the whole country, it is difficult to determine
whether these differences reflect the local endemic status.

Immunization status
Written immunization records were available for 213 out of 965
children (22.1%). One hundred ninety eight children were
vaccinated with three doses of hepatitis B vaccine, and 34 children
were immunized on the day of birth or the following day. Five outof 213 children with immunization records were HBsAg positive(2.35%; 95% CI: 0.30–4.40%), while 12 of 752 without
immunization records were HBsAg positive (1.60%; 95% CI:
0.70–2.49%). The differences between the two groups were notsignificant (p = 0.46).

Discussion
HBsAg prevalence among the general population
The estimated HBsAg prevalence in the general population wasmuch lower in both children and adults than that of previous
reports from neighboring countries and Lao PDR. For example,
HBsAg prevalence in adults in Cambodia, Thailand, and Vietnam
was reported to be 7.7% (95% CI: 6.2%–9.3%) [12], 6 to 10%[15,20], and 18.8% (95% CI: 15.7%–21.9%) [13], respectively.
Data on HBsAg prevalence amongst children was relatively scarce,and reported to be 3.5% (95% CI: 2.4%–4.8%) in Cambodia [21],and 18.4% (95% CI: 13.4%–23.4%) in Vietnam [13]. In Lao
PDR, studies in blood donors, hospitalized patients, and Lao
migrant workers tested in Thailand showed HBsAg prevalence of
8.73% (95% CI: 8.69%–8.77%) [22], 17.99% (95% CI: 17.81%–
18.17%) [23], and 6.86% (95% CI: 6.80%–6.92%) [24] basedon the given numerators and denominators in the articles,
respectively.
Since the study objective was to estimate the nationwide HBsAg
prevalence among the general population of Lao PDR, and thus

Potential risk factors
Our survey revealed that no potential risk factors weresignificantly associated with the children’s infection status, withthe exception of the mothers’ hepatitis B infection status. HBsAg
prevalence surveys in other countries revealed that history ofsurgery [26,27], level of education [26], and ethnicity [28] wereindependently associated with hepatitis B infection. The reason
why we could not find any potential risk factors positively
associated with hepatitis B infection among children is not clear.
However, it should be noted that the primary objective of thepresent study was to assess HBsAg prevalence, and not its risk
factors. Additionally, some reports found that HIV positive
individuals are positively associated with hepatitis B virus infection

Table 2. HBsAg prevalence among children (5 to 9 years old) and mothers (15 to 45 years old).

Children’s
HBsAg (+)%

95% CI

Standard
error

DesigneffectMothers’
HBsAg (+)%

95% CI

Standard
error

DesigneffectHigh coverage
districts(n = 486)6

1.14

0.23–2.04

0.44

0.82

18

3.79

1.79–5.79

0.97

1.24

Low coverage
districts(n = 479)

11

2.39

0.75–4.03

0.79

1.27

9

1.88

0.49–3.37

0.69

1.22

Total (n = 965)

17

1.72

0.81–2.63

0.44

1.10

27

2.93

1.65–4.20

0.61

1.28

doi:10.1371/journal.pone.0088829.t002

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Table 3. Unadjusted and adjusted odds ratio for being HBsAg positive among children from five to nine years old in Lao PDR by
selected background characteristics.

Unadjusted
odds ratio
DPT3 coverage

high

95% CIp

Adjustedodds ratio

95% CIp

0.73–6.21

0.16

3.47

0.77–15.64

0.10

0.28–1.78

0.44

0.87

0.31–2.47

0.79

0.67–5.40

0.22

1.41

0.26–7.72

0.68

0.67–3.36

0.30

1.03

0.27–3.89

0.96

0.37–3.64

0.80

0.60

0.18–1.96

0.38

0.21–2.62

0.63

0.65

0.21–2.08

0.46

0.39–2.49

0.97

0.79

0.28–2.21

0.64

9.45–61.07

0.00

28.13

10.21–77.53

0.00

1(reference)

low

2.13

Mothers’ age

15 to 291(reference)

30 to 45

0.70

Ethnicity

Low land Lao1(reference)others1.90

Educationnone

1(reference)

finished primary school or upper

1.50

Occupation

white collar1(reference)blue collar

1.15

Sex

male

1(reference)

female0.75

Birth place

health facility1(reference)

non-health facility

0.98

Mothers’ HBsAg

negative1(reference)

positive24.02

doi:10.1371/journal.pone.0088829.t003[29,30]; however, we did not investigate HIV due to limited
budget.

PDR achieved the target through the immunization program
alone because the country has the lowest immunization coverageof all countries in the region [7,9]. Considering the relatively lower
HBsAg seroprevalence among the mothers compared to thosereported in previous studies, it is likely that Lao PDR had a lower
prevalence even before the introduction of the hepatitis B
immunization program. Therefore, the final target of reducing
HBsAg prevalence to less than 1% in children aged at least 5 years
could be difficult to achieve if the country simply continues its
current immunization policy.
A nationwide prevalence survey targeting the general population is ideally conducted before implementing the immunization

WHO’s regional target
The interim target of the WHO is to reduce HBsAg prevalence
to less than 2% in children aged at least 5 years old by 2012 [7,31].
The point prevalence is used for monitoring the control ofhepatitis B. The Regional Office for the Western pacificrecommended that the country conduct a national HBsAg
prevalence survey to verify whether the country has reached theregional prevalence target [9]. Following these criteria, Lao PDR
had already achieved its goal. However, it is unlikely that Lao

Table 4. Unadjusted and adjusted odds ratio for being HBsAg positive among mothers from 15 to 45 years old in Lao PDR by
selected background characteristics.

Unadjusted
odds ratio
DPT3 coverage

high
low

0.50

Mothers’ age

15 to 291(reference)

30 to 45

1.03

Ethnicity

Low land Lao1(reference)others0.80

Educationnone

1(reference)

finished primary school or upper

1.68

Occupation

white collar1(reference)blue collar

1.71

History of surgery

no1(reference)

yes

1.28

95% CIp

Adjustedodds ratio

95% CIp

0.20–1.28

0.14

0.47

0.19–1.16

0.10

0.43–2.51

0.94

0.94

0.39–2.25

0.88

0.30–2.17

0.65

0.68

0.25–1.85

0.44

0.70–4.01

0.23

2.04

0.89–4.68

0.09

0.53–5.55

0.35

1.93

0.68–5.50

0.21

0.39–4.25

0.67

1.30

0.35–4.78

0.68

1(reference)

doi:10.1371/journal.pone.0088829.t004

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Hepatitis B Prevalence in Child and Mother Pairs

females was 6.2% [22]. When considering the disease burden ofhepatitis B virus infections, it is better to include both sexes [26].
To the best of our knowledge, this is the first nationwide,
population-based serological survey on chronic hepatitis B virus
infections both before and after implementation of hepatitis B
immunization in Southeast Asia, where disease burden is high. As
such, our results provide valuable information on a hepatitis B
immunization program and a useful baseline against which tocompare future assessments in this region.
National immunization policy should be based on the disease
epidemiology [3]. However, in Southeast Asia, understanding of
the epidemiology of hepatitis B remains unsatisfactory. Even whena country implements a hepatitis B immunization program forchildren and the prevalence of disease reaches the target (i.e., lessthan 2% among children aged 5 years or older), we cannot
conclude that the immunization program alone contributed toreduced disease prevalence without comparing it to the diseaseprevalence in the pre-vaccine generation, i.e., adults. Nationwide
surveys assessing disease prevalence in the generations before andafter the implementation of a vaccination program will provide
valuable information for understanding hepatitis B epidemiology.
Therefore, we recommend surveying hepatitis B seroprevalence inboth generations.

strategy to evaluate hepatitis B epidemiology. However, we wereable to understand the epidemiology to some degree, even after
implementation of immunization policy, because adults usually
represent the pre-vaccination era [15,17].

Strengths of the study
The present study is the first nationwide survey on theprevalence of hepatitis B in the general population both before
and after the implementation of a hepatitis B immunization policyin Lao PDR and other Southeast Asian countries. We applied
multistage stratified cluster sampling to better represent thegeneral population. The design effect of prevalence was calculated
between 0.8 and 1.3, which was acceptable as we set it around 2.0
before the survey.
The background characteristics of our sampled population weresimilar to those of another nationwide population-based study, theLao PDR Reproductive Health Survey (LRHS) [32] conducted in
2005. For example, the locations of current residence (north,central, and south) were 33.3%, 41.7%, and 25.0% in our survey,
and 38.6%, 38.9%, and 22.5% in the LRHS. The levels of
mothers’ completed education (none, primary school, secondary
school or more) were 31.9%, 38.9%, and 29.2% in our survey, and28.8%, 43.7%, and 27.5% in the LRHS. The LRHS applied themultistage stratified cluster sampling method and surveyed morethan 13,000 women all over the country. A direct comparison of
the populations sampled by the two different surveys is difficult toperform as the primary objectives were different. Despite this, oursampled population is considered to likely represent the general
population in Lao PDR.

Conclusions
We determined the nationwide HBsAg prevalence amongchildren (1.7%; 95% CI: 0.8%–2.6%) and their mothers (2.9%;
95% CI: 1.6%–4.2%) in Lao PDR. This is the first report toestimate the nationwide prevalence of chronic hepatitis B in preand post-hepatitis B immunization generations in Southeast Asia,
where hepatitis B infections are a substantial burden. The
estimated prevalence was below that of previous studies, suggestingthat our understanding of this disease’s epidemiology is lacking
and warrants further investigation. We recommend that theprevalence among the pre- and post-vaccine eras should be
investigated when conducting hepatitis B seroprevalence surveys.

Limitations of the study
There are several limitations in our study that should be
addressed. First, the population data is based on the census
conducted in 2005. After 2005, the population distribution may
have changed and some of the villages could have merged, thereby
creating bias in the findings. Fortunately, we did not survey any
villages that disappeared or merged.
Second, floating or marginal populations are likely to be missedfrom the residential lists, and these populations could be a sourceof HIV and hepatitis B virus infections [33]. In futureseroprevalence surveys, these subpopulations should be accounted
for by using specific approaches, such as oversampling.
Third, population immunity levels were difficult to measure or
estimate. The possession of immunization certificates was low,
because many participants had already finished their scheduled
vaccinations before 12 months of age, and relevant documents
were lost. In the present study, we did not have enough data fromhealth centers due to time and budget limitations. Since we did not
examine immunization markers, such as HBsAb, herd immunity
levels are unknown.
Lastly, adult men were not included in the survey. Serologicalstudies in the past indicated that men have higher HBsAg rates
than women [8,21,28]. In Lao PDR, male blood donors presented
with 9.7% HBsAg positive prevalence, while the prevalence inAcknowledgments
We would like to express our sincere thanks to the sampled children,
mothers, and caregivers for their voluntary participation in the survey. We
are grateful to all of the surveyors and supervisors from the National
Immunization Program, National Center for Laboratory and Epidemiology, Ministry of Health, and staff from the provincial and district
Departments of Health. We would also like to thank Dr. H. Murakami foradvising on the survey methodology, and Drs. S. Noda, Y. Sugiura, H.
Okabayashi, A. Iwamoto, and M. Anami for their critical comments
regarding the field survey, and Dr. Y. Horikoshi for geographical analysis.

Author Contributions
Conceived and designed the experiments: AX MH KI TW MS. Performed
the experiments: KK TK PV CP KP DP BS VSO TS. Analyzed the data:
KK TK MH. Contributed reagents/materials/analysis tools: KI TW MS.
Wrote the paper: AX PV MH. Revised the manuscript: KK TK PV CP
KP DP BS VSO KI TW MS. Arranged laboratory for diagnosis: PV KI
TW MS.

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International Journal of Infectious Diseases 36 (2015) 21–26

Contents lists available at ScienceDirect

International Journal of Infectious Diseases
journal homepage: www.elsevier.com/locate/ijidSeroprevalence of chronic hepatitis B, as determined from dried blood
spots, among children and their mothers in central Lao People’s
Democratic Republic: a multistage, stratiﬁed cluster sampling survey
Kenichi Komada a, Masaya Sugiyama b, Phengta Vongphrachanh c, Anonh Xeuatvongsa d,
Bouaphan Khamphaphongphane c, Tomomi Kitamura a, Tomoko Kiyohara e,
Takaji Wakita e, Hitoshi Oshitani f, Masahiko Hachiya a,*a

Bureau of International Health Cooperation, National Centre for Global Health and Medicine, 1-21-1, Toyama, Shinjuku-ku, Tokyo 162-8655, Japan
Department of Hepatic Diseases, Research Centre for Hepatitis and Immunology, National Centre for Global Health and Medicine, Ichikawa, Chiba, Japan
National Centre for Laboratory and Epidemiology, Vientiane Capital, Lao PDRdNational Immunization Program, Vientiane Capital, Lao PDReDepartment of Virology II, National Institute of Infectious Diseases, Tokyo, Japanf
Department of Virology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japanbc

A R T I C L E I N F O

S U M M A R Y

Article history:
Received 24 February 2015
Received in revised form 28 April 2015
Accepted 29 April 2015

Background: There is limited information regarding the prevalence of hepatitis B in Lao PDR, where thehepatitis disease burden is substantial. Thus, reliable seroprevalence data is needed for the disease,
based on probability sampling.
Methods: A stratiﬁed, multistage, cluster sampling survey of hepatitis B surface antigen (HBsAg)
positivity among children aged 5–9 years and their mothers aged 15–45 years was conducted.
Participants were selected randomly from the central region of Lao PDR via probability-proportional-tosize sampling. Blood samples were collected onto ﬁlter paper and subsequently analyzed using achemiluminescent microparticle immunoassay.
Results: A total of 911 mother-and-child pairs were collected; the seroprevalence of HBsAg wasestimated to be 2.1% (95% conﬁdence interval 0.8–3.4%) among children and 4.1% (95% conﬁdence
interval 2.6–5.5%) in their mothers after taking into account the sampling design and the weight of eachsample. The children’s HBsAg positivity was positively associated with maternal infection and beingborn in a non-health facility, while the maternal infection status was not associated with any
background characteristic.
Conclusions: Lao PDR has a relatively lower HBsAg prevalence in the general population compared tosurrounding countries. To ensure comparability to other countries and to future data, rapid ﬁeld tests arerecommended for a nationwide prevalence survey.
 2015 The Authors. Published by Elsevier Ltd on behalf of International Society for Infectious Diseases.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).

Keywords:
Hepatitis B
Seroprevalence
Dried blood spots
Chemiluminescent microparticle
immunoassay
Probability sampling
Southeast Asia

1. Introduction
According to the World Health Organization (WHO) estimate,approximately 360 million people worldwide have a chronic
hepatitis B virus (HBV) infection,1,2 and almost half of these
individuals live in the Western Paciﬁc Region, which comprises
only approximately 28% of the global population.3 Every year, anestimated 620 000 people die from HBV-related diseases,1 and over
90% of them had acquired the virus decades earlier at birth or* Corresponding author. Tel.: +81-3-3202-7181 (ext. 2722); fax: +81-3-3205-7860.
E-mail address: m-hachiya@it.ncgm.go.jp (M. Hachiya).

during early childhood.4,5 In 1992, the WHO recommended thatchildhood hepatitis B vaccination be included in the immunization
programs of all countries.6 The Regional Committee for the WHO
Western Paciﬁc Region adopted this recommendation in 2005,
calling for a reduction in chronic hepatitis B infection to less than
2% among 5-year-old children as an interim milestone towards theﬁnal regional goal of less than 1% by 2012.7 To achieve this goal, it
was recommended that the birth dose coverage be improved to
65% and the third dose of hepatitis B vaccination coverage be
improved to 85%.8
Hepatitis B surface antigen (HBsAg) is a serological marker ofhepatitis B infection and can be detected during the acute andchronic phases of the disease. Therefore, HBsAg seroprevalence

http://dx.doi.org/10.1016/j.ijid.2015.04.020
1201-9712/ 2015 The Authors. Published by Elsevier Ltd on behalf of International Society for Infectious Diseases. This is an open access article under the CC BY-NC-ND
license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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usually reﬂects the presence of chronic hepatitis B in a given
population, and a serological survey of this marker is recommended to measure the impact of immunization policies.2
Lao People’s Democratic Republic (Lao PDR) is a landlocked
country located in the centre of the Indochina Peninsula. Since 90% of
the land is covered by mountains with deep forest and 80% of thetotal population lives in rural areas, health services are difﬁcult toprovide in Lao PDR. In addition, because the country is bordered byhepatitis B hyperendemic countries such as Cambodia,9 China,10Myanmar,10,11 Thailand,12 and Vietnam,13 Lao PDR has been
considered an endemic country.14,15 The country initiated its
expanded program on immunization (EPI) in selected regions in
1984, and the program became available nationwide in the mid1990s. According to a report from the Ministry of Health, Lao PDR,
immunization coverage for bacille Calmette–Guérin (BCG), the third
oral polio vaccine, the third diphtheria, pertussis, tetanus, hepatitis B
vaccine, and the ﬁrst measles vaccine was 60%, 46%, 45%, and 36%,
respectively, in 2004. Hepatitis B vaccination was included in the EPI
in 2002. Hepatitis B vaccination for newborns was integrated into
the EPI starting in 2004; this gradually expanded from central
hospitals to rural areas. There have been no previous reports on theinfection rates of chronic HBV in the general population. Therefore,
population-based seroprevalence surveys for hepatitis B are
warranted to better estimate the current prevalence of hepatitis B
and to evaluate the impact of immunization policies that focus on
preventing mother-to-child transmission.2,8There is limited information regarding the prevalence of hepatitis
B in Lao PDR, indicating the need for a population-based household
survey to provide a reliable seroprevalence for the disease. However,the sparsely distributed population, less developed infrastructure,and limited human and ﬁnancial resources in Lao PDR make theconducting of surveys difﬁcult. Filter paper blood collection is simple
and inexpensive, and the storage and transport methods are easy.
HBsAg testing with dried blood spots (DBS) is suitable for large-scale
surveys in resource-limited countries.16,17
The Ministry of Health in Lao PDR plans to conduct a nationwide
hepatitis B prevalence survey in the near future. Therefore, it was
proposed that a household survey be conducted, as a pilot survey,
in the central region of the country, where the infrastructure andtransportation are relatively better than in the rest of the country.
The primary objectives of this survey were to: (1) assess theoperational and programmatic feasibility of a population-based
sero-epidemiological survey, and (2) estimate chronic hepatitis B
infection rates, as determined from the HBsAg seroprevalence
among children and their mothers.
2. Materials and methods
The ﬁeld work for the survey was carried out at the end ofJanuary 2011 and lasted for 10 days. The study used a multistage,stratiﬁed, random cluster sampling design. The sample wasrestricted to children aged 5 to 9 years, and their mothers aged
15 to 45 years on January 1, 2011. The children had to bebiologically related to their mothers and not adopted. The rationale
for the target age group of children used in this survey was basedon the fact that the risk of acquiring chronic HBV infection ishighest in the ﬁrst 5 years of life,4,15 as observed in theneighbouring hyperendemic countries.
2.1. Sample size
The sample size was calculated based on the expected HBsAg
seroprevalence rate of 15% among children and their mothers. The
sample size of 960 was calculated at a 5% level of signiﬁcance witha precision of 3.5%. The design effect for cluster sampling was
assumed to be 2.0 with a response rate of 85%.

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2.2. Sampling
Four provinces and the Vientiane Municipality in the central
region of Lao PDR, which account for 2.5 million people (approximately 40% of the total population), were selected for the study. The
population of Vientiane Municipality is 691 721, of Borikhamxay
Province is 225 301, of Khammuane Province is 337 390, of Vientiane
Province is 388 895, and of Savannakhet Province is 825 902. There
are nine districts in Vientiane Municipality, six in Borikhamxay
Province, nine in Khammuane Province, 13 in Vientiane Province,and 15 in Savannakhet Province.
Provinces were considered as strata, yielding a total of ﬁve
strata. In the ﬁrst stage of sampling, four districts were selected
randomly from each stratum using probability-proportional-tosize (PPS) based on the population data from the 2005 census
conducted in Lao PDR. In the second stage, two villages wereselected randomly from each selected district by PPS, and a total of
40 villages, as clusters, were selected. Twenty survey teams wereformed, and each team comprised a supervisor and two surveyors,nominated from the district health staff. If surveyors could notreach the designated village due to obstacles such as ﬂoods or
mudslides, the nearest village on the way back to the district centre
from the designated village could be selected as an alternative. In
each selected village, surveyors developed a list of households that
had children aged from 5 to 9 years based on the data from thepoverty reduction program, EPI, or other relevant residential lists.
From these lists, 24 households were selected randomly via alottery, and the youngest child within the eligible age range andhis/her mother were sampled for the survey. Adopted children
were excluded from the lists.
2.3. Questionnaires
A brief face-to-face questionnaire was administered to thesampled mothers. Information was collected on the demographic
status and history of the child (i.e., age, sex, place of birth, andimmunization history), as well as the socioeconomic status of thechild’s household, as measured by the maternal educational
background and occupation of the household head. Additionally,questions regarding exposure to potential risk factors for acquiring
hepatitis B infection (e.g., surgery, blood transfusion, and sharing
toothbrushes) and history of past hepatitis infection among otherfamily members were asked.
2.4. Testing for HBsAg
Capillary blood was collected onto Whatman 903 ﬁlter paper
protein saver (Whatman, Maidstone, Kent, UK) via a ﬁnger prick andair-dried for at least 60 min; ﬁlter papers were kept in sealed plasticbags and transported to Japan. DBSs were stored at ambient
temperature in Lao PDR for 7 to 10 days after sample collection, andthereafter at 4 8C for 3 months prior to being tested at the
Hepatology Research Centre, National Centre for Global Healthand Medicine. Blood samples were extracted from DBSs by punching
two bloodstained circles 3 mm in diameter and eluting overnight in
500 ml of phosphate-buffered saline (pH 7.2). Eluates were tested for
HBsAg using a chemiluminescent microparticle immunoassay(Architect i2000SR; Abbott Diagnostics, IL, USA). The relative light
unit (RLU) value of each sample was detected with an automatedsystem. The sample was considered to be positive for HBsAg basedon comparisons to the RLU value of a calibration sample.
2.5. Consent, conﬁdentiality, ethical considerations, and safety issues
The surveyors explained the detailed survey objectives andprocedures to the local authorities and selected mothers and資料 6: 掲載論文 / Annex 6: Publication

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K. Komada et al. / International Journal of Infectious Diseases 36 (2015) 21–26

children verbally and in writing. Written informed consent was
obtained from the parents or legal representatives if mothers were
illiterate. Informed consent, questionnaires, and the blood collection
process were supervised by provincial- and national-level supervisors. The survey proposal was reviewed and approved by the ethics
committees of the Ministry of Health, Lao PDR, and the National
Centre for Global Health and Medicine, Japan (NCGM-950).

for HBsAg positivity. All estimates and standard errors were
adjusted for the multistage clustered sampling design to ensure
representative and unbiased results. A p-value of <0.05 wasconsidered statistically signiﬁcant.
3. Results
Forty villages from 20 districts in central Lao PDR were selected
for the study. The survey teams successfully visited all of the
40 selected villages and conducted the questionnaire and serosurvey. Of the 960 selected mother-and-child pairs, 49 were not eligible
for analysis and were excluded from the study (35 pairs did not meetthe study age requirement for the child (e.g., 3–4 years old or
unknown), 13 pairs did not meet the study age requirement for themother (e.g., >45 years old or unknown), and one pair did not have ablood sample from the child (reason unknown)). Thus, a total of
911 mother-and-child pairs were included in this analysis.
The baseline characteristics of the selected mothers and theirchildren are summarized in Table 1. The mean age of the mothers
was 32.4 years (95% CI 32.0–32.8 years), and the mean age of thechildren was 6.7 years (95% CI 6.7–6.8 years). Of the children
sampled, 453 (49.7%) were male and 458 (50.3%) were female. One
hundred and seventy-one children out of 911 had written
immunization records at the survey. Among these, immunization

2.6. Data entry and analysis
All of the completed questionnaires were taken to a centralized
location, and to reduce any data entry-related errors, the double
data entry method was performed in a Microsoft Excel worksheet(Microsoft Ofﬁce 2007) along with validation and correction.
STATA 12 (Stata Corp., College Station, TX, USA) was used for thedata analysis. Calculations of the overall prevalence amongchildren and mothers took into account the individual weight ofeach sample. The Poisson exact method for rare events was used to
calculate the 95% conﬁdence interval (CI) of HBsAg prevalence foreach region. Chi-square and Fisher’s exact tests were used to
examine the relationships between the independent variables and
HBsAg positivity in the bivariate analysis. Multiple logistic
regression models were used to investigate the independent
predictors of different households and individual characteristics

Table 1
Prevalence of HBsAg among children and mothers in the central region of Lao PDR by selected background characteristics
Children (5–9 years old)n(%)

HBsAg-positive

Mother’s age, years (n = 911)9(0.99)
0
15–20
97(10.65)
1
21–25
26–30
274
(30.08)8266(29.20)6
31–35
177(19.43)4
36–40
88(9.66)
2
41–45
Mother’s ethnicity (n = 911)
783
(85.95)19
Lowland Lao
83(9.11)
1Highland Lao
Hmong5(0.55)
140(4.39)
0Unknown
Main transportation to the nearest health facility (n = 906)78
(8.61)
1
On foot
23(2.54)
1
Bicycle554(61.15)15
Motor bike120
(13.25)2
Car120(13.25)
1
Hand tractor
Other11(1.21)
1
Time to nearest health facility (n = 876)
174
(19.86)8
10 min386(44.06)
4>10 to 30 min
162(18.49)5>30 to 60 min
154(17.58)4>60 minMother’s education level (n = 911)178
(19.54)2
No education
Primary school404(44.35)14201(22.06)
4
Junior high school
113(12.40)1
High school13(1.43)
0
College2(0.22)
0
Other or unknown
Occupation of household head (n = 911)
589
(64.65)13
FarmerFisherman
4(0.44)
0118(12.95)
4
Labourer112(12.29)1
Public ofﬁcer
8(0.88)
0
Factory employee
19(2.09)
0
General employee
54(5.93)
3
Merchant
7(0.77)
0
Other
Family history of liver diseases except mother (n = 911)
Yes
95
(10.43)1
816(89.57)20
No

Mothers (15–45 years old)%

95% CIHBsAg-positive%

95% CI

0.00%
1.03%
2.92%
2.26%
2.26%
2.27%

(0.00–3.01)(0.91–4.93)(0.46–4.05)(0.05–4.47)(0.00–5.45)

0
5
13
14
6
2

0.00%
5.15%
4.74%
5.26%
3.39%
2.27%

(0.68–9.63)(2.22–7.28)(2.56–7.96)(0.70–6.08)(0.00–5.45)

36
3
0
1

4.60%
3.61%
0.00%
2.50%

(3.13–6.07)(0.00–7.71)

2.43%
1.20%
20.00%
0.00%(1.35–3.51)(0.00–3.60)(0.00–75.53)

1.28%
4.35%
2.71%
1.67%
0.83%
9.09%

(0.00–3.83)(0.00–13.36)(1.35–4.06)(0.00–3.99)(0.00–2.48)(0.00–29.35)

5
0
21
8
4
2

6.41%
0.00%
3.79%
6.67%
3.33%
18.18%(0.85–11.97)

4.60%
1.04%
3.09%
2.60%

(1.45–7.74)(0.02–2.05)(0.39–5.78)(0.06–5.14)

10
17
8
5

5.75%
4.40%
4.94%
3.25%

(2.25–9.24)(2.35–6.46)(1.57–8.31)(0.42–6.08)

1.12%
3.47%
1.99%
0.88%
0.00%
0.00%

(0.00–2.69)(1.67–5.26)(0.04–3.94)(0.00–2.64)

5
18
10
6
1
0

2.81%
4.46%
4.98%
5.31%
7.69%
0.00%

(0.36–5.26)(2.43–6.48)(1.94–8.01)(1.11–9.51)(0.00–24.45)

2.21%
0.00%
3.39%
0.89%
0.00%
0.00%
5.56%
0.00%

(1.02–3.40)

19
0
6
7
0
2
6
0

3.23%
0.00%
5.08%
6.25%
0.00%
10.53%
11.11%
0.00%(1.79–4.66)

1.05%
2.45%

(0.00–3.14)(1.39–3.51)

4
36

4.21%
4.41%

(0.98–8.32)(3.00–5.82)(0.08–6.70)(0.00–2.66)(0.00–11.87)(0.00–7.56)(2.20–5.39)(2.14–11.19)(0.08–6.59)(0.00–45.36)(1.06–9.11)(1.70–10.80)(0.00–25.72)(2.45–19.77)

HBsAg, hepatitis B surface antigen; CI, conﬁdence interval.

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K. Komada et al. / International Journal of Infectious Diseases 36 (2015) 21–26

Table 2
HBsAg prevalence among children and their mothers by province

Vientiane Municipality(n = 186)
Vientiane Province(n = 182)
Borikhamxay Province(n = 179)
Khammuane Province(n = 180)
Savannakhet Province(n = 184)
Total(n = 911)Children (5–9 years
old)n = 911

Mothers (15–45 years
old)n = 911

2.15%
4
2.75%
5
3.91%
7
1.11%
2
1.63%
3
2.09%
21

3.76%
7
6.59%
12
5.59%
10
2.78%
5
3.26%
6
4.06%
40

(0.05–4.25)(0.35–5.14)(1.04–6.78)(0.00–2.66)(0.00–3.48)(0.79–3.38)(1.00–6.52)(2.95–10.23)(2.19–8.98)(0.35–5.20)(0.67–5.85)(2.58–5.54)

HBsAg, hepatitis B surface antigen.

coverage for BCG was 95%, for the third oral polio vaccine was 88%,
for the third diphtheria, pertussis, tetanus, hepatitis B vaccine was
87%, and for the ﬁrst measles vaccine was 80%.
Of the 911 pairs included in the study, 21 children and
40 mothers were positive for HBsAg. Eleven out of 21 HBsAgpositive children (52.3%) had HBsAg-positive mothers, whereas theother 10 were from non-infected mothers. The prevalence wascalculated as 2.1% (95% CI 0.8–3.4%) in children and 4.1% (95% CI
2.6–5.5%) in their mothers after taking into account the sampling
design and the weight of each sample (Table 2). HBsAg prevalence
varied by province, but the differences among provinces were notstatistically signiﬁcant for either children or mothers. In calculating HBsAg prevalence, the design effects were determined to be
1.6 for children and 1.1 for mothers (Table 2).
To determine whether background characteristics affect HBsAg
status, a logistic regression analysis was conducted. For thechildren, maternal HBsAg positivity and being born in a non-healthfacility were positively associated with hepatitis B infection(Table 3), whereas the other potential risk factors were not. For
Table 3Adjusted odds ratio for being HBsAg-positive among children aged 5 to 9 years in
the central region of Lao PDR by selected background characteristics
Characteristics (Reference group)

Adjusted OR

95% CI

Address (Khammuane)
1.06(0.23–5.00)
Vientiane Capital
0.94(0.11–7.88)
Vientiane Province
Borikhamxay
1.64(0.31–8.76)
0.88(0.07–10.63)
Savannakhet
Mother’s HBsAg status (Negative)
31.31(12.23–80.16)
Positive
Mother’s age (15–30 years)
0.87(0.10–7.50)
31–45 years
Mother’s education level (None)
2.83(0.33–24.49)
Finished primary school or upper
Occupation of household head (Other)
2.14(0.60–7.65)
Labourer
Family history of liver diseases except mother’s (None)
0.98(0.05–18.70)
Yes or unknown
Time to nearest health facility (10 min)
1.89
(0.70–5.09)<10 minSex (Female)
Male
1.92
(0.67–5.47)
Birth place (Health facility)
3.01(1.06–8.72)
Non-health facility
History of HepB vaccination at birth (None or unknown)
2.58(0.31–21.71)
Received
History of HepB vaccination (Never or less than twice)
0.48(0.12–1.92)
Received 3 times
Sharing tooth brush (Never)Yes or unknown
1.25(0.36–4.33)

Technical Report vol.05 Hepatitis B Prevalence Survey in Lao PDR

Characteristics (Reference group)

Adjusted OR

95% CI

Address (Khammuane)
1.03(0.21–4.91)
Vientiane Capital
2.12(0.42–10.63)
Vientiane Province
1.82(0.38–8.67)
Borikhamxay
1.23(0.28–5.41)
Savannakhet
Age (15–30 years)
0.86(0.45–1.65)
30–45 years
Mother’s education level (None)
1.35(0.25–7.43)
Finished primary school or upper
Occupation of household head (Other)
1.44(0.41–5.06)
Labourer
Family history of liver diseases except mother herself (None)
0.73(0.14–3.82)
Yes or unknown
Time to nearest health facility (10 min)1.35
(0.59–3.05)<10 minHistory of surgery (Never)
2.11(0.83–5.41)
Yes or unknown

p-Value
0.973
0.338
0.426
0.763
0.633
0.709
0.538
0.689
0.450
0.111

HBsAg, hepatitis B surface antigen; OR, odds ratio; CI, conﬁdence interval.

the mothers, no background characteristic was associated with
HBsAg positivity (Table 4).
To evaluate the potential risk factors for children acquiring achronic hepatitis B infection without vertical transmission, logistic
regression analysis was conducted for children born from HBsAgnegative mothers (n = 871). A history of regular hepatitis B
vaccination (scheduled at 6, 10, and 14 weeks after birth) was
negatively associated with the children’s HBsAg status (p = 0.04),
while immunization after the delivery (within 24 h) was not. Otherrisk factors, including birth place, did not show any signiﬁcantassociation with HBsAg status among children (Table 5).
4. Discussion
To the best of our knowledge, this is the ﬁrst population-based,cross-sectional survey to estimate chronic hepatitis B prevalence
among the general population in Lao PDR. The major ﬁndings
were: (1) the questionnaire and serosurvey using multistage,

p-Value
0.934
0.949
0.537
0.916
0.000a
0.894
0.319
0.222
0.987
0.193
0.207
0.039a
0.357
0.279
0.706

HBsAg, hepatitis B surface antigen; OR, odds ratio; CI, conﬁdence interval.
ap < 0.05.

60

Table 4
Adjusted odds ratio for being HBsAg-positive among mothers aged 15 to 45 years in
the central region of Lao PDR by selected background characteristics

Table 5Adjusted odds ratio for being HBsAg-positive among children aged 5 to 9 years born
to HBsAg-negative mothers in the central region of Lao PDR by selected backgroundcharacteristics
Characteristics (reference group)

Adjusted
OR

95% CI

Mother’s age (15–30 years)
1.36(0.37–6.05)
31–45 years
Mother’s education level (None)
3.93(0.45–33.11)
Finished primary school or upper
Occupation of household head (Other)
3.96(0.65–23.01)
FarmerFamily history of liver diseases (None)
1.17(0.11–7.74)
Yes or unknown
Time to nearest health facility (10 min)
3.00
(0.64–13.78)<10 minSex (Female)
Male
3.97
(0.80–19.12)
Birth place (Health facility)
1.38(0.29–6.58)
Non-health facility
History of HepB vaccination at birth (Not received or unknown)
2.89(0.50–15.72)
Received
History of regular HepB vaccination (2 times or unknown)
0.11(0.13–0.93)
3 times
Sharing tooth brush (Never)Yes or unknown
2.04(0.37–10.68)

p-Value

0.665
0.212
0.133
0.887
0.160
0.088
0.683
0.226
0.042a0.404

HBsAg, hepatitis B surface antigen; OR, odds ratio; CI, conﬁdence interval.
ap < 0.05.

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K. Komada et al. / International Journal of Infectious Diseases 36 (2015) 21–26

stratiﬁed random cluster sampling was carried out successfully inthe central region of Lao PDR; (2) the estimated prevalence in thegeneral population was 2.1% in children and 4.1% in women ofchildbearing age; and (3) HBsAg positivity in mothers was
positively associated with HBsAg positivity in their children,
whereas no condition was signiﬁcantly associated with HBsAg
positivity in mothers.
4.1. Feasibility of the household survey
Multistage, stratiﬁed, random cluster sampling is the mostreliable strategy for accurately estimating the prevalence of healthstatus and conditions among the general population within adeﬁned geographical area under constraints of limited time andresources.18 However, in Lao PDR, this sampling strategy has rarely
been applied for these purposes. For example, EPI coverage,19
measles immunization coverage,20 antenatal care,21 energy
malnutrition,22 and smoking23 have been assessed via conveniencesampling rather than random sampling methods. The exact
reasons for not using a probability sampling methodology are
not clear. One exception is the Lao Reproductive Health Survey
2005, which focused on population and development planning.24
The Lao Reproductive Health Survey 2005 used a two-stage,stratiﬁed cluster sampling method for the household survey andreported standard errors and design effects for each value
measured.
The present survey was conducted successfully in terms ofoperational and programmatic feasibility, because the datacollection was completed within 10 days with response rates of
100%, and the calculated design effects were 1.1 to 1.6 for HBsAg
prevalence. This sampling methodology can be applied for otherpurposes as well.
4.2. HBsAg seroprevalence among children and their mothers
There have been no previous reports on the prevalence ofhepatitis B in the general population of Lao PDR. The prevalence ofchronic hepatitis B, as determined by HBsAg, has been reported
previously in blood donors25 and hospitalized patients.26 However,this selection of individuals may result in biased ﬁndings, as they
may not be representative of the general population. For example,
HBsAg prevalence among blood donors may be higher than that in
the general population when donors are paid and lower when they
are unpaid.27
The surrounding Southeast Asian countries have previously
been considered as highly endemic areas for hepatitis B. For
instance, data from Cambodia,9 China,10 Myanmar,10,11 Thailand,12
and Vietnam13 suggest a prevalence of 8–10%. The results of thepresent study revealed a lower prevalence than expected. There
are a few reasons to explain this ﬁnding. First, the central part of
Lao PDR is different from other regions (e.g., better health services
and cultural differences). Second, the sensitivity of HBsAg testingon blood collected on Whatman 903 ﬁlter paper in the ﬁeld setting
may be low. Lastly, the high temperature and humidity may havedamaged the HBsAg protein prior to analysis.

25

hepatitis-infected children. A potential risk factor for this was thenumber of routine hepatitis B vaccinations (2 times; Table 5).
This is important, especially in a country such as Lao PDR, where
the rate of delivery by a skilled birth attendant is less than 30%. The
WHO emphasizes that hepatitis B immunization should be given
during the ﬁrst 24 h after delivery; however, a ﬁrst vaccinationeven at >24 h may greatly contribute to the prevention of hepatitis
B infection from horizontal sources. Moreover, the importance ofregular immunization during infancy cannot be overemphasized.
4.4. Study limitations
There are several limitations that need to be discussed. First, thesurvey design, which applied PPS, was based on population datafrom the latest national census in 2005. Since 2005, the populationof the country has increased from 6 200 000 to 6 600 000, and thenumber of districts has increased (separated) from 141 to
143. During the same period, the number of villages has decreased(merged). However, no updated population data have been madeavailable since 2005. Therefore, the present study may have underor over-estimated the population in selected villages. Moreover,the hepatitis B immunization policy has expanded over the last
10 years, and therefore our sampled children may have, in part,
represented the pre-vaccine era.
Another limitation of this study is that the seroprevalence
survey was conducted using Whatman 903 ﬁlter paper. HBsAg isheat-stable and resistant to drying,28,29 and DBSs are convenient
and relatively cheap, thus DBSs have been used previously forseroprevalence surveys on hepatitis B.17,30,31 However, thesensitivity and speciﬁcity of ﬁeld samples are still not well
documented. Therefore, DBS ﬁeld test results should be comparedto other methods like ELISA and rapid tests in the future.
Additionally, seroprevalence surveys should be repeated overtime, along with hepatitis B control measures, and the methodology should ideally be comparable to that used in neighbouring
countries and areas. Given the comparability of the results, the useof a widely available rapid ﬁeld test, such as the Alere Determine
HBsAg test card (Alere Medical Co., Ltd, Chiba, Japan),9 isrecommended for nationwide surveys. The sensitivity andspeciﬁcity of the Determine rapid test have been reported as
97–100% and 100% from ﬁeld studies in Vietnam32 and China,33
thus the rapid test is recommended by the WHO.34
4.5. Conclusions
In the present study, an HBsAg prevalence survey targetingchildren and their mothers was conducted successfully in thecentral part of Lao PDR. The prevalence was estimated to be 2.1%
(95% CI 0.8–3.4%) for children aged 5 to 9 years, and 4.1% (95% CI
2.6–5.5%) for mothers aged 15 to 45 years, after taking into accountthe sampling design and the weight of each sample. The prevalenceof hepatitis B in Lao PDR was found to be lower than that in other
Southeast Asian countries, as well as the prevalence reported inprevious studies conducted in Lao PDR. Given the comparability of
the ﬁndings, the use of an HBsAg rapid test is strongly
recommended for future nationwide surveys.

4.3. Risk factors for acquiring hepatitis B
Acknowledgements
The present study revealed the mother’s HBsAg status andchild’s place of birth to be signiﬁcantly associated with the child’s
infection status (Table 3). Other risk factors, such as male child,9ethnicity,13 family history of liver diseases,9 and the place ofresidence9,13 were found not to be associated. This may be theresult of the limited sample size.
The HBsAg positivity results for the children and their mothers
indicated that transmission was horizontal in almost half of the

We would like to express our sincere thanks to the sampledchildren, mothers, and caretakers for their voluntary participationin the survey, and the village leaders and Women’s Union at allsites for their arrangements and contribution. We gratefully
acknowledge all the surveyors and supervisors from the National
Immunization Program and National Centre for Laboratory andEpidemiology, Ministry of Health, and the staff from provincial andテクニカル・レポート vol.05 ラオス人民民主共和国における B 型肝炎有病率調査61

資料 6: 掲載論文 / Annex 6: Publication

26

K. Komada et al. / International Journal of Infectious Diseases 36 (2015) 21–26

district departments of health. We thank Dr H. Murakami for his
supervision of the entire survey process, Drs H. Okabayashi, A.
Iwamoto, and M. Anami for their critical comments on the ﬁeld
survey, and Dr Y. Horikoshi for the geographical analysis.
Funding source: This work was supported by a Grant for The
National Centre for Global Health and Medicine (22-7 and 27-4).
The funding source was not involved in the study design, in thecollection, analysis and interpretation of data, in the writing of themanuscript, or in the decision to submit the manuscript for
publication.
Ethical approval: The surveyors explained the detailed survey
objectives and procedures to the local authorities and selectedmothers and children verbally and in writing. Written informed
consent was obtained from the parents or legal representatives if
mothers were illiterate. Informed consent, questionnaires, and theblood collection process were supervised by provincial- andnational-level supervisors. The survey proposal was reviewed andapproved by the ethics committees of the Ministry of Health, Lao
PDR, and National Centre for Global Health and Medicine, Japan(NCGM-950).
Conﬂict of interest: The authors have no conﬂict of interest
regarding this research.
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Original Article

DOI: 10.5582/bst.2013.v7.4.178

Factors affecting childhood immunization in Lao People's Democratic
Republic: A cross-sectional study from nationwide, populationbased, multistage cluster sampling
Tomomi Kitamura1,*, Kenichi Komada1, Anonh Xeuatvongsa2, Masahiko Hachiya1
12

Bureau of International Medical Cooperation, National Center for Global Health and Medicine, Shinjuku, Tokyo, Japan;
Ministry of Health, Vientian, Lao People's Democratic Republic.

Summary

Vaccines are one of the most important achievements in public health, and a major
contributor to this success is the Expanded Programme on Immunization (EPI). The
effective vaccination series of the EPI should be used by its target population. Various
factors influence the utilization of the EPI vaccination series. In Lao People's Democratic
Republic (Lao PDR), immunization coverage was lower than the regional average. This
study evaluates risk factors affecting immunization underutilization among children
five to nine years of age. It is a cross-sectional study from nationwide, population-based,
multistage cluster sampling. The children who have received 'standard six' antigens andthose who have been partially immunized are compared. In a bivariate analysis, household
occupation, maternal age, means of transportation, time to the nearest health facilities,
the child's birthplace, birth attended by medical staff, and notification of vaccination dateby medical staff, village authority, or megaphone were associated with vaccination status.
The final multivariate logistic regression model revealed that maternal age and notificationof vaccination date by the village authority increased the odds of full vaccination, while
notification of vaccination date by megaphone had decreased those odds. Further detailed
qualitative research may be needed to discover how maternal sociodemographic factors
influence the utilization of these services. Future research needs to target younger children
and must include health care provider factors related to vaccination services.
Keywords: Expanded programme on immunization (EPI), full vaccination, childhood vaccination

1. Introduction
Vaccines have substantially reduced the global burden of
infectious diseases. They are considered one of the mostimportant achievements in public health and one of themost cost-effective preventive services for children (17). The major contributor to this success is the Expanded
Programme on Immunization (EPI) of the World HealthOrganization (WHO), United Nations Children's Fund
(UNICEF) and Global Alliance Vaccine Initiative (GAVI)(6). The EPI was launched in 1974 as a worldwide*Address correspondence to:Dr. Tomomi Kitamura, Bureau of International Medical
Cooperation, National Center for Global Health andMedicine, 1-21-1, Toyama, Shinjuku, Tokyo 162-8655,
Japan.
E-mail: tkitamura.imcj@gmail.com

alliance of collaborating nations whose goal was toexpand immunization services and coverage (6).
The success of EPI does not only depend on effective
vaccination series, but also on achieving optimal use by
its target population and high immunization coverage(4,8). Pinpointing non-vaccination factors is important
for achieving the EPI targets (9,10). The utilizationof vaccination services depends on numerous factors
such as provision of EPI services including outreachservices, accessibility of these services, number ofhealth workers, availability of safe needles, syringes,
and cold chain, as well as health education andknowledge and attitude of mothers (5,11,12). Once achild enters the vaccination system, completion of theseries is determined by the mother's educational level,
employment status, experience with vaccination services,
adequate schedule information, immigration status, andoverall socioeconomic status (13-15). Various factors

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BioScience Trends. 2013; 7(4):178-185.
are important for the initiation and completion of thevaccination series.
The EPI was initiated in Lao People's Democratic
Republic (Lao PDR) in 1979 (16). This programme
greatly contributed to the progress of basic immunization
coverage through the support of international
partners and the government of Japan (17). However,immunization coverage in Laos PDR became stagnant
after the WHO Western Pacific Region achieved regional
polio eradication in 2000 (17). Immunization coverage
was lower than regional average: measles immunization
coverage among 1-year-olds was 64%, diphtheria
tetanus toxoid and pertussis (DTP3) immunization
coverage among 1-year-olds was 74%, hepatitis B(HepB) immunization coverage among 1-year-olds was
74%, tuberculosis (Bacille Calmette-Guérin vaccine:BCG) immunization coverage among 1-year-olds was
72% and polio (OPV3) immunization coverage among
1-year-olds was 76% (18,22). The risk factors for nonvaccination need to be studied to achieve optimal useof the vaccination services in Lao PDR. Therefore, theaim of this study is to evaluate risk factors affecting
underutilization of childhood immunization amongchildren five to nine years of age.
2. Material and Methods
2.1. Study location and population
Lao PDR is located in Southeast Asia and bordered by
five countries: Burma, China, Vietnam, Cambodia, andThailand. In 2010, its population was approximately 6.2
million and its under-five mortality rate was 54 out of
1,000 live births (19).
2.2. Sampling and sampling frameThis analysis has been done in the sub-population of
the nation-wide survey for Hepatitis B sero-prevalence.
All 143 districts in Lao PDR were stratified into two
strata according to their immunization coverage. Twelve
districts were randomly selected from each stratum,and two villages were selected from each district via
probability of population proportional to size sampling.
After randomly selecting 21 children (five to nine years
old) and their mothers (15 to 45 years old) from theselected villages, questionnaires were administered.
One thousand and eight pairs of mothers and children
were recruited and assessed for eligibility for this study.
Forty-three pairs were excluded either because mothers
were younger than 15 years of age or older than 45 yearsof age, or children were younger than five years of age
or older than nine years of age. Four hundred and sixtyfive pairs were excluded because they did not havevaccination certifications such as yellow cards or motherand child handbooks. Three pairs were excluded because
possession of the vaccination certification was unknown.

Among the 497 pairs with the vaccination certification,
284 pairs were excluded because they could not show
their certification on the day of the survey. From this,213 pairs were included in this study.
In Lao PDR, the yellow cards or mother and childhandbooks are provided to children who received any
vaccination regulated by the Laos PDR Ministry of
Health. Vaccination dates were transcribed from thosecards, and any vaccination documentation was consideredsufficient evidence (20). Each child's immunization
record was checked against the EPI immunization
schedule recommended by the WHO (21,22). The
following categories were used: fully immunized, if the"standard six" antigens ‒ BCG, DTP3 (3 doses), OPV3
(3 doses), and measles vaccines ‒ have been received on
the day of interview; and partially immunized, if at least
one recommended vaccine dose was not given (23,24).
This study compared factors between children who
completed their standard vaccinations (full vaccination)and children who had not completed their vaccinations at
the time of the survey (partial vaccination).
2.3. Collection of data
The survey, which used a face-to-face, interviewbased questionnaire, was conducted from 25 January
2012 to 4 February 2012 by a survey team. A pilot
study was conducted prior to the survey to check forclarity and consistency of the questionnaire. The survey
team collected demographic information, vaccination
status, and other relevant information. Each survey
team had two surveyors. These surveyors received
two days of training, which consisted of an overview
of research methods, interview strategies, and ethicalconsiderations. Before each interview, written consent
was obtained from the child's mothers and vaccination
dates were transcribed from yellow cards or mother andchild handbooks.
2.4. Statistical analysis
The proportions of children who received all therecommended routine vaccination according to thepolicy of the Expanded Programme of Immunization(EPI) in Lao PDR and its 95% confidence interval (CI)were calculated. Bivariate analysis was performed toassess the relationship between vaccination status and its
risk factors. A chi-square test was used for categoricalvariables and Student's t test was used for continuous
variables. Crude odds ratios (ORs) and 95% CIs were
calculated. Based on the results of the bivariate analysis),all significant factors and ethnicity were entered into
the multivariate logistic regression analysis. Ethnicity
was added to the final multivariate model because its
diversity presented a major challenge in health service
delivery due to cultural and language barriers. However,the variable "birthplace of the children" was excludedwww.biosciencetrends.com

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Figure 1. Study profile.

from the final multivariate logistic regression analysis
since it showed the highest multicollinearity among thevariables in the model. Multicollinearity was detected byusing the variance inflation factor (VIF). Stata version
11.0 was used to perform all statistical analyses.
2.5. Ethical considerations
The survey was reviewed and approved by the EthicalCommittee of the Ministry of Health, Lao PDR,
and the institutional review board of the National
Center for Global Health and Medicine, Japan(NCGM-G-001130-00). Access to selected households
was granted by the Ministry of Health and theprovincial and district government authorities.
3. Results
3.1. Study profile of all subjects
Figure 1 shows the profile of research subjects. 213
pairs were eligible. The case (full vaccination) grouphad 172 children and the control (partial vaccination)group had 41 children. The proportion of children,
aged five to nine, who hold certificates of vaccination(either a yellow card, a mother and child handbook, orboth) was 49.3% of the sample, while the proportionof children with an eligible record of vaccination was
21.1% of the sample (data not shown).
3.2. Proportion of children vaccinated by antigen
The statistics of children vaccinated with each antigen
are presented in Table 1. All vaccination rates wereover 80% except for the HepB birth dose, which

Table 1. Proportion of children having received the various
EPI antigens according to vaccination cards
EPI antigen
HepB0
BCG
OPV1
OPV2
OPV3
DPT1
DPT2
DPT3
MV1
Full vaccination***Total (%), (n = 213)

95%CI

19.2
97.2
97.7
94.8
93.4
98.6
95.8
93.4
83.6
80.8

13.9-24.6
94.9-99.4
95.6-99.7
91.8-97.8
90.1-96.8
97.0-100
93.1-98.5
90.1-96.8
78.6-88.6
75.4-86.1***Full vaccination – BCG, diphtheria-tetanus perttusis (DTP) (3 doses),polio (3 doses), and measles vaccines

was 19.2%. Among those 19.2%, only five children
received the birth dose on the day of birth or the nextday. The dates for the HepB birth dose for the rest of
the children (80.8%) were not accurate. This low rate
and record confusion may be due to the fact that the
HepB vaccination for newborns was integrated into the
EPI in 2004, which gradually expanded from central
hospitals to rural areas. Most (80.8%) of the children
were fully immunized between the ages of five andnine, according to the recommended EPI schedule.
3.3. Risk factors of childhood immunization
Among the sociodemographic factors of the family,
household occupation, maternal age, means oftransportation, and time to the nearest health facilities
were associated with full vaccination of the children(Table 2). Birthplace of the children and birth attended
by medical staff were associated with vaccination
status (Table 3). Notification of vaccination date bywww.biosciencetrends.com

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Table 2. Risk factors of childhood immunization (sociodemographic factors)
Items

Full vaccinationn = 172, (%)

Partial vaccinationn = 41, (%)

Crude OR (95%CI)

p-valueEthnicity
Lowland Lao
Midland Lao
Highland Lao

102 (59.3)
61 (35.5)
9 (5.2)25 (61.0)
14 (34.2)
32 (4.9)

Reference
1.07 (0.52-2.21)
1.10 (0.22-5.43)

0.86
0.90

Household occupation
farmernot farmers

126 (73.3)
46 (26.7)

35 (89.7)
4 (10.3)

Reference
0.31 (0.10-0.94)

0.03

Mean maternal age (years)

32.7 (CI; 31.8-33.7)

29.3 (CI; 27.5-31.2)

Maternal education
no education
primary school
junior high school
high school
university

68 (39.5)
55 (32.0)
34 (19.8)
10 (5.8)5 (2.9)16 (39.0)
19 (46.3)
4 (9.8)1 (2.4)1 (2.4)

Reference
0.68 (0.32-1.45)
2.00 (0.62-6.45)
2.35 (0.28-19.73)
1.18 (0.13-10.78)

0.32
0.25
0.43
0.89

Sex of children
boygirl
unknown

74 (43.0)
97 (56.4)
1 (0.6)21 (51.2)
41 (46.3)
1 (2.4)0.69 (0.34-1.38)
Reference

0.29

Mean number of children

3.4 (CI; 3.1-3.7)

3.2 (CI; 2.6-3.9)

Transportation
walkbicyclebikecartractorboat
N/A

65 (37.8)
3 (1.7)44 (25.6)
27 (15.7)
33 (19.2)
0 (0)
0 (0)

13 (31.7)0 (0)18 (43.9)0 (0)5 (12.2)
3 (7.3)2 (4.9)Mean time to the nearest health facilities (minutes)

29.5 (CI; 25.0-33.9),
n = 15248.1 (CI; 20.5-75.7),
n = 3736 (20.9)129 (75.0)
4 (2.3)2 (1.2)1 (0.6)9 (22.0)29 (70.7)
3 (7.3)
0 (0)
0 (0)

Reference
1.11 (0.48-2.56)
0.33 (0.06-1.76)

0.80
0.20

Decision-maker for vaccination
FatherMotherGrandparents
Village leader
Others0.00

0.71
Reference
0.49 (0.22-1.10)

0.08

1.32 (0.43-4.02)

0.63

0.02

N/A; Non applicable, CI; 95% condence interval.

Table 3. Risk factors of childhood immunization (delivery history)
Items

Full vaccinationn = 172, (%)

Partial vaccinationn = 41, (%)

Crude OR (95%CI)

p-value

Birth place of children
provincial hospital
district hospital
health centre
private clinic
homebush near house
N/A

38 (22.1)
24 (14.0)
4 (2.3)2 (1.2)72 (41.9)
31 (18.0)
1 (0.6)3 (7.3)9 (16.9)
1 (2.4)1 (2.4)26 (63.4)
0 (0)1 (2.4)

Reference
0.21 (0.05-0.86)
0.32 (0.03-3.80)
0.16 (0.01-2.29)
0.22 (0.06-0.77)

0.03
0.36
018
0.02

Birth attended by the medical staff
yes
no
N/A

94 (54.7)
77 (44.8)
1 (0.6)

14 (34.2)
26 (63.4)
1 (2.4)2.27 (1.09-4.69)
Reference

0.02

Birth attended by the village health volunteer
yes
no
N/A

32 (18.6)
137 (79.7)
3 (1.7)3 (7.3)37 (90.2)
1 (2.4)2.88 (0.83-10.10)
Reference

0.08

Birth attended by the traditional birth attendant
yes
no
N/A

33 (19.2)
136 (79.1)
3 (1.7)9 (22.0)30 (73.2)
2 (4.9)0.81 (0.35-1.87)
Reference

0.62

Birth attended by the family member
yes
no
N/A

75 (43.6)
95 (55.2)
2 (1.2)19 (46.3)
19 (46.3)
3 (7.3)0.79 (0.39-1.60)
Reference

0.51

Birth attended by nobody
yes
no
N/A

4 (2.3)167 (97.1)
1 (0.6)2 (4.8)38 (92.7)
1 (2.4)0.46 (0.08-2.60)
Reference

0.36

N/A; Non applicable, CI; 95% condence interval.

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Table 4. Risk factors of childhood immunization (source of information of vaccination)
Items

Full vaccinationn = 172, (%)

Partial vaccinationn = 41, (%)

Crude OR (95%CI)

p-value

Source of information of vaccination (medical staff)
yes
no
N/A

129 (75.0)
43 (25.0)0 (0)32 (78.1)
7 (17.1)
2 (4.9)0.66 (0.27-1.60)
Reference

0.35

Source of information of vaccination (informationon the vaccination cards)
yes
no
N/A

51 (24.8)
117 (68.0)
4 (1.3)9 (22.0)30 (73.2)
2 (4.9)1.45 (0.64-3.29)
Reference

0.37

Source of information of vaccination (family
member or friends)
yes
no
N/A

40 (23.3)
129 (75.0)
3 (1.7)14 (34.2)
26 (63.4)
1 (2.4)0.58 (0.27-1.21)
Reference

0.14

Source of information of vaccination (TV)
yes
no
N/A

67 (39.0)102 (59.3)
3 (1.7)13 (31.7)
27 (65.9)
1 (2.4)1.36 (0.66-2.84)
Reference

0.40

Source of information of vaccination (local
authority)
yes
no
N/A

97 (56.4)
72 (41.9)
3 (1.7)28 (68.3)
12 (29.3)
1 (2.4)0.58 (0.27-1.22)
Reference

0.14

Source of information of vaccination date (medical
staff)
1. yes
2. no
N/A

33 (19.2)
138 (80.2)
1 (0.6)18 (43.9)
23 (56.1)
00.31 (0.14- 0.64)
Reference

0.00

Source of information of vaccination date (village
health volunteer)
yes
no
N/A

62 (36.1)
108 (62.8)
2 (1.2)24 (58.5)
16 (39.0)
1 (2.4)

1.16 (0.57-2.36)
Reference

0.68

Source of information of vaccination date (local
authority)yesno

170 (98.8)
2 (1.2)38 (92.7)
3 (7.3)

6.71 (1.05-42.7)
Reference

0.02

Source of information of vaccination date (woman's
union)yesno

78 (45.4)
94 (54.7)

19 (46.3)
22 (53.7)

0.96 (0.48-1.90)
Reference

0.91

Source of information of vaccination date (official
letter from district governor)
yes
no
N/A

27 (15.7)
144 (83.7)
1 (0.6)6 (14.6)
35 (85.4)
0

1.09 (0.42-2.86)
Reference

0.85

Source of information of vaccination date(megaphone)yesno40 (23.3)
132 (76.7)

20 (48.8)
21 (51.2)

0.32 (0.15-0.66)
Reference

0.00

Source of information of vaccination date (poster)yesno27 (15.7)
145 (84.3)

5 (12.2)
36 (87.8)

0.57 (0.48-3.74)
Reference

0.57

N/A; Non applicable, CI; 95% condence interval.

medical staff, village authority, or megaphone was also
associated with full vaccination (Table 4).
Based on the bivariate analysis all variables
significantly associated with full vaccination status
and ethnicity were included in the multivariate logistic
regression model. The results revealed that maternal
age and obtaining information of the vaccination dateby the village authority increased the odds of full
vaccination. However, obtaining information on thevaccination date by megaphone had decreased the odds

of full vaccination (Table 5).
4. Discussion
This study highlights the factors associated with thevaccination status of children aged five to nine in
Lao PDR. Multivariate analysis of the risk factors
for childhood immunization showed that maternal
age and notification of the vaccination date by thevillage authority were positively associated with fullwww.biosciencetrends.com

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BioScience Trends. 2013; 7(4):178-185.
Table 5. Factors associated with full vaccination of children (logistic regression); occupation of household head-grouped
Factors

Adjusted odds ratio

95%CI

p-value

Sociodemographic factors
Ethnicity
Household occupation
Maternal age
Transportation to the health facility
Time to the nearest health facility

1.321
0.269
1.087
1.174
0.989

0.575-3.036
0.067-1.085
1.008-1.172
0.852-1.618
0.977-1.001

0.512
0.065
0.031
0.327
0.076

Delivery history
Birth attended by medical staff

2.617

0.936-7.317

0.067

Source of EPI information
Source of information of vaccination date by medical staff
Source of information of vaccination date by local authority
Source of information of vaccination date by megaphone

0.422
17.4300.204

0.150-1.185
1.827-166.280
0.065-0.637

0.102
0.013
0.006

immunization. Notification of the vaccination dateby megaphone was negatively associated with fullimmunization.
4.1. Sociodemographic factors
According to the bivariate analysis, maternal age wasassociated with vaccination status. Furthermore, there
was a linear trend that showed that full vaccination
increases with maternal age. However, the relationshipbetween childhood immunization and maternal age
varies in the literature. There are some studies that showthat maternal age was not associated with childhood
immunization (6). One study from Africa showed theinfluence of younger maternal age on the utilisation of
medical care (8).
This study did not show that maternal education
was associated with vaccination status, which may
be due to the contextual effects of maternal education
on children's immunization in Lao PDR (25). Many
studies have shown that maternal education or literacy
is positively associated with the vaccination status of
the children (1,6,8,9,13,25). In addition, some studies
showed that the mother's knowledge of specificimmunizations was associated with full vaccination(3,5,17). However, in Mali, Koumaré et al. reported nodifference associated with parental knowledge about
EPI diseases and full vaccination (3). In India, Parashar
showed that literate women in a village may influenceother women's capacity to seek and take advantage
of state-provided healthcare, and even children of
uneducated mothers may have better health knowledge
due to residential or employment proximity to literate
women through social influence (25). Further detailed
research is needed to determine why maternal education
was not associated with childhood immunization in thiscontext.
Maekawa et al. showed that distance to healthfacilities in a rural region of Lao PDR was associatedwith vaccination status (17). This study focused ontime rather than distance to health facilities sinceaccess depends on not only the distance but also
the accessibility of the road and the availability oftransportation. Therefore, mean time to the nearest
health facilities was associated with full vaccination
status in the bivariate analysis; however, it was not
significant in the logistic regression model, which may
be due to the established nationwide outreach serviceof EPI (26). Further research is needed to explore
the association of vaccination status and the actual
accessibility to the vaccination sites, combining precise
information on distance, time to the vaccination sites,
and availability of transportation.
4.2. Delivery history
Birth attended by medical staff was associated withfull vaccination of the children; however, it was not
significant in the multivariate analysis. According
to Maekawa et al., bivariate analysis showed that
immunization status was associated with whether
mothers obtained information on immunisation before
delivery; however, this factor was not significant in themultivariate analysis (17). Maekawa et al. also revealed
that household visits and receipt of information before
delivery influenced the number of fully immunizedchildren . Further analysis revealed that household visits
contributed to higher full-vaccination rates, especiallyamong illiterate mothers. Therefore, it may not be
sufficient to give information only once before or after
the delivery; it might be better to provide information
over several household visits.
4.3. Source of EPI information
The notification of the vaccination date by villageauthority had higher odds of full vaccination. On theother hand, notification of the vaccination date by
megaphone was negatively associated with vaccination
status. These results show that comprehensive andappropriate information dissemination may be key for
vaccinating children against the EPI diseases (3,6).
There are several strengths in this study. This
information has been collected through a nationwide
survey using multistage cluster sampling. Geographically,
the survey dissemination covered a wide portion ofwww.biosciencetrends.com

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BioScience Trends. 2013; 7(4):178-185.

Lao PDR and the ethnic minorities. A sampling frame
allowed sampling bias to be a minimum. Only written
records were used to avoid inaccuracies in vaccination
history. Yellow cards and mother and child handbooks
were the sole source of immunization informationin this study. Parent's recall was not included in
the interview. Rodewald et al. stated that the gold
standard for measuring vaccination status, other thanserological testing to detect immunity, is a parentlinked and provider-validated immunization statusmeasure (2). Parent-linked means that parents nameall immunization providers and provider-validated
means obtaining the immunization records for eachchild and combining those data into a single record.
Multiple studies have documented the inaccuracy ofparents as the sole source of immunization status. The
single-provider record check method, used in this study,lies between the parental recall and the parent-linked,
provider-verified measure. The validity of this method
depends on the frequency and reliability with which
immunizations are included in the medical records (2).
However, this study has several limitations. Firstly,
this analysis has been done in the sub-population of thenation-wide survey for Hepatitis B sero-prevalence andonly included the children and mothers who possessed
any certifications of vaccination; therefore, the numberof children in full and partial vaccination is skewed
and no immunization or risk factor information was
included from the children without the vaccination
certifications. Second, the target of this study was
children five to nine years old, which is older than thenormal target population for a risk factor-based study.
Thirdly, this study did not focus on health care provider
factors, which may influence the vaccination status.
Utilization of vaccination services is dependent onsociodemographic factors of the target population, as
well as the number of health workers and availabilityof safe needles and syringes (5). Two studies show thatchildren missed immunizations due to the provider'sreluctance to vaccinate children while sick or when
visiting health care centres for other purposes (9,28).
This study did not focus on these provider risk factors.
Lastly, this is a cross-sectional study; therefore, it isdifficult to generate cause-and-effect relationships ofchildhood immunization and risk factors due to thestudy's design.
In conclusion, this study reinforces the importanceof appropriate means of notification or provision of
information on vaccination services in order to ensure
full immunization (13). In the policy and programme
level in Lao PDR, it may be necessary to implement
appropriate information system on vaccination services
at the community level such as mobilizing the villageauthorities. Older mothers showed higher odds of
having fully immunized children, however, othersociodemographic factors such as maternal education
was not associated with vaccination status. Further

detailed qualitative research may be needed to discover
how this factor influences vaccination services,along with other maternal sociodemographic factors
such as education. Future research needs to target
younger children to accurately collect information
on vaccination records and other sociodemographic
factors. Future studies also have to include health careprovider factors that affect vaccination services.
Acknowledgements
This research was supported by Grants of the National
Center for Global Health and Medicine from the
Ministry of Health, Labour, and Welfare, Japan (25-8).
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Technical Report vol.05

テクニカル・レポート vol.05
ラオス人民民主共和国における B 型肝炎有病率調査

Hepatitis B Prevalence Survey in Lao PDR

執筆者：

This report was prepared by:

木多村知美

Tomomi Kitamura, MD, MPH

和田 耕治

Koji Wada, PhD, MD, MSc

駒田 謙一

Kenichi Komada, MD, MPH

蜂矢 正彦 ( 主任研究者 )Masahiko Hachiya, PhD, MD, MPH (principal

本研究は国際医療研究開発費 22 指 7、25 指 8、27 指 4 により実施された。

investigator)

This work was supported by The Grant of National
Center for Global Health and Medicine (22-7, 25-8, 27-4).

国研究開発法人 国立国際医療研究センター
国際医療協力局

National Center for Global Health and〒 162-8655 東京都新宿区戸山 1-21-1
電話：81-3-3202-7181 / ファクス 81-3-3205-7860
info@it.ncgm.go.jp
www.ncgm.go.jp
2014 年 3 月初版 発行
2016 年 1 月第 2 版 発行

Medicine, Japan

Bureau of International Health Cooperation
1-21-1 Toyama, Shinjuku, Tokyo 162-8655, JAPANTel : 81-3-3202-7181 / Fax : 81-3-3205-7860
info@it.ncgm.go.jp
www.ncgm.go.jp
Issued in March, 2014（the 1st edition),in January, 2016 (the 2nd edition)©National Center for Global Health and Medicine, Japan All Rights Reserved.