Jpn. J. Infect. Dis., 54, 27‑30, 2001

Epidemiological Report

Evaluation of the Japanese School Health Surveillance System for Influenza
Hiroshi Takahashil *, Hayato Fujii2, Nahoko Shindol and Kiyosu Taniguchil･ 3
1Infectious Disease Surveillance Cen ter and2Field Epidem iology Train ing Program, National Institute of lnfectious Diseases,

Toyama 1‑2311, Shinjuku‑ku, Too,0 162‑8640, Japan and3Communicable Disease Surveillance and Response, World Health Organization,
Avenue Appia 20, 1211 Geneva 27, Switzerland(Received January 10, 2001. Accepted March 8, 2001)
SUMMARY: In order to evaluate the Japanese nationwide school absenteeism surveillance system f♭r pediatricinnuenza in comparison with the national sentinel surveillance for influenza, weused surveillance guidelines(Centers for Disease Control and Prevention, 1998) to determine the efficacy of the school health surveillancesystem (SHSS)･ Data regarding school absenteeism (age 4‑15 years old) was compared with data regarding
influenza‑like illness (ILI) per sentinel sites during the se.cond to the 1 lth weeks of 1998 and 1999･ Despite thesystem's high simplicity and acceptability, telecommunlCation costs were estimated at US$ 490,000 (1998).
Representativeness of schoolchildren was ye.ry accurate, but ILI for pre‑school children (4‑6 years) remained

uncountable･ Sensitivity, specificity, and posltlVe Predictive value of the SHSS compared to sentinel surveillance
were calculated as 80%, 100%, and lO0%, respectively (P‑0.004). Although the SHSS was found to provide
accurate surveillance data during periods of high influenza activity, non‑innuenza virus infections (e.g.,adenovims, rotavims,.and NoⅣalk vims, etc･) may become mixed in the SHSS data･ Evaluation using thissystem should be contlnued employlng a new Case definition excluding gastrointestinal symptoms.

innuenza activlty lnCreaSed substantially during the 1 997‑

INTROD tJC TION

1998 and 1998‑1999 seasons (5,6). We evaluated the effec‑
tiveness of the SHSS in measunng the impact of the influenza

Mass vaccination or a schooトaged population has beenreported to have considerable effect in reducing the magnitude

epidemic in J叩an.

of an influenza epidemic (1 ), and future institution of massvaccination of the pediatric population is being vlgOrOuSlyMETHODS

discussed in the United States (US) (2). In Japan, mass influ‑enza vaccination was recomended to schoolchil血en in 1 962,

We compared the effectiveness of the SHSS with theand universal influenza vaccination of children aged between

Influenza Sentinel Surveillance System (ISSS) Conducted in

7‑ 1 5 years was implemented as a national irrmumizatiOn policy
in 1976 (3)･ HoweTer, in 1987, this policy was reduced tothe National EpidemiologlCal Surveillance for Infectious
Diseases programuslng data aom these two severeinfluenza

voluntary vaccination because of a lack of data supporting

seasons･ h Japan,the ISSS is the pnmaryinfluenza suⅣeillance

the effectiveness of uniyersal influenza vaccination (4), andmass influenza vaccinat10n tO schoolchildren was eventually

sampling f♭r virological tests (Fig. 1 ).

system. The accuracy or those data are assured by 〜10%

stopped in 1994.

Guidelines for suⅣeillance evaluation (Centers for Disease

The importance ofpediatric innuenza surveillance isunder‑emphasized. Improved influenza surveillance is essential tounderstanding the disease burden, aS well as to assesslng theNatio 匁

effectiveness of the vaccination of schoolchildren against

7F宥WFV fﾆ詛V7F薮W2 Disc

Dep一rtmeDt0ー→Ⅰnfectio 白influenza.

F6U2
Se

Virol〇gy一一Surye‖一 匁6T6TB

ter

The school health surveillance system (SHSS) is the sole
notifiable suⅣeillance system in Japan forpediatric influenza.

The SHSS has beenrun by the Mimistry of Education, Science,Sports and Culture (MOE) and Minis叫ofHealth and Welfare

Pref 坊7GW&(MO出) since the school health law was enacted in 1958. The(regiorL

objective of the SHSS is to measure the magnitude of influena
among schoolchildren. If absenteeism exceeds 20% as reported

韮epartnentofHealthﾆ疋ﾇ&T7F薮W2 dise&sesuryeilbl)CeCenter)to the SHSS, the school pnnclpal and teachers discuss closure
JurisdictionaI Put)lie Health Centerof a class or school to prevent further absenteeism.
The SHSS has not been evaluated in its role as a commu‑
nicable disease suⅣeillance system. According to the National

EpidemlOglCal Surveillance of Infectious Diseases program,S 坊'F匁RⅠnterTIa 友躍ｦﾆIsiteS(aptnediciJle

絣ﾃ襴VFG&2*Corresponding author: Tel: +81‑3‑5285‑I I 1 I ext. 2538, Fax:+81 ‑3‑5285‑1 129, E‑mail: hiroshit@nih.gojp

Fig. 1. Structure of the NationaHnnuenza Sentinel Surveillance System.

27

Control and Prevention lCDC]) were employed for the study

CentralGovernnent(7). Since we focused on influenza trends in schoolchildren,
data from children aged 4‑ 1 5 years old were compared.

Mi■血tryor→Mimisb'yorバEA)thーEdLJCAtionh the ISSS, epidemic influenza statusis defined as exceed‑ing 10 innuenza‑like illness (ILI) patients per sentinel site

per week. For the SHSS, we defined epidemic status as greaterthan 1 00 absentees per 1 00,000 persons. Age‑stratified popu‑

Pre 貿V7GW& 牌 fW&贅 ent

lation censuswas obtained from the Summary of the National

Deprtm一n 免Census, 1998 (8).

JlcJLJfb

RESUIXSｸ

ХH

6ﾂionCom 蒙鉾FVRｲJurisdictional Education Committee

The usefulness of the SHSS was evaluated in terms ofsimplicity,flexibility, representativeness, and timelinessaccording to the CDC's evaluation guideline.

Kindergarten 墜VﾆVﾒ

Simplicity and爪exibiLity: Because the SHSS is a symptom‑

aAdJun 末 &eAtarySChool,ghschoolbased suⅣeillance system, teachers and school nurses simply

count the number of children presenting with ILI symptoms

Fig･ 2･ Stmcture orthe National School Health SuⅣeiHance System.

in their class/school. No extra staff are employed for infor‑
mation collection. Because the teachers and nurses have tocall each absentee's home during the observation period, Sometelecommunication cost is incurred (approximately US$490,000 in the 1998‑1999 season). The SHSS has long beenused as a decision‑making tool for class/school closure andis also highly acceptable for infectious disease surveillance.

Representativeness: Since schools are distributed throughl
out J叩an, and all ILI cases are counted, representation of theincidence of disease is assumed to be very accurate. However,of the schooトattending population, children with ILI aged

between 4‑6 yeaqsare not alwaysincluded.Kindergarten educa‑tion is not compulsory in Japan and not a few children stayhome or attend part time.

Timeliness: The surveillance period for the SHSS is from
October to April each season. Data are not available during

the 52md week to the lst week because orNew Year's break.
It takes 2 Weeks f♭r the data to be gathered completely at theMinistry level, and an additional 1‑2 weeks are needed toFig･ 3･ Weekly number of influenza‑like illness among 4‑1 5 year‑oldssummarize and feedback the results through the National

in Japan, 1976‑1999.

InfectiousDisease Surveillance Center website (Fig. 2).

We first checkedrise, peak, and fall of epidemic curve forILIfrom the SHSS during the period of 1976 to 1999. Twentylrl=r̲㍗L ̲

one out of 23 influenza epidemic peaks occurred during the0 棚皿皿孤8棚狐o胡

2nd to the l lth week of仇ese years (Fig. 3). We then checked

the correlation ofdatafrom the ISSS and the SHSS of these(gtx)L･EduBPQTL8才｢weeks in 1998 and 1999. We obseⅣed a strong positive rela‑tion (Fig. 4).

Sensitivity) specirICity7 and positive predictive value:
The number of chil血en with ILI per sentinel site and numberof absent children per loo,000 are summarized in Table 1. For
the 20 weeks in the two seasons, epidemics were observed

during 12 weeks by both the ISSS and SHSS･ Sensitivity,specificity, and positive predictive value of the SHSS
compared to ISSS are calculated as 80% (12 out of 1 5 weeks),
100% (12/12 weeks), and lOO% (5/5 weeks), respectively'InLtuenza‑like illness ≦ 15 years old per site

(Fisher's exact test, P ‑ 0.004).
Fig･ 4･ Comlation between school absenteeism and ILI* per sentinel,
1997‑1999, Japan.

DISCUSSION
In the mid‑1970s in some areas in the US, use ofschool‑
based absenteeism was validated a洗er sustained excess schoolsuⅣeillance data in Japan.

absenteeism was fわund to be an adequate indicator of theMost influenza surveys focuslng On schools have beenpresence and extent of influenza (9, I 0). Ours is the first study

conducted on a small scale and have not observed a period

for evaluation of the nationwide school heath surveillance

longer than one season. A consistent finding with influenza

system for influenza compared to laboratory‑assisted sentinelin communities is that influenza･ occurs first among school‑28

Table 1. Sentinel surveillance and school absenteeism, Japan, 1997‑1999
97/98 season

close suⅣeillance, and further monitor for strengthening of theSHSS will contribute to improvedunderstanding of the impact

98/99 seasonof influenza in schoolchildren and in entire communities inS en tincI S chooI S entinel Schoo I

Japan･IL I/s i te ab senteei sm ILI/s i te absenteeism/▲U 3 4 つJ O 7 4 7 8 ′bWeek 2Week 3

2 0 0 6 2 5 4 6 2 L 3 9 7 5 6 0 0 ｣ 9 3 0 (XU 2 0 2 ′hUO 4 07 0ノ

2 0ノ 0 4 2 ′LU O 1 6 4 9 2 L 8 7 8 8 L

l つJ 4 4 2 1

1 2 2 2 1 tl 1 1L 30767529

tJ tJ 5 つJ O 5 0 0 つJ O

Week 4
Week 55 0 2 9 L 5 6 2 4 5 8 0‑1 7 6 7 3 5 6 8

4 5 0 1‑′0 ‑ 7 1 つJ 2

ACKNOWLEDGMENTS

7 1 4 0 4 0 3 3 ′b

1 0 つJ ′hU 'I

2 tJ つJ tJ tJ 2 1This study was planned and developed under support of al

Japanese Ministry of Health and Welfare scientific research

Week 6

grant on "coordination for the national and prefectural surveil‑

Week 7lance systems" (H 1 2‑Shink0‑5).

Week 8
Week 9REFERENCE S

Week 10

Week ll

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sentinel site.

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or epidemics.

A disadvantage orthe SHSS is that no standardized casedefinition for ILI absenteeism exists. An effective influenza(in Japanese).

4. Ministry ofHealth and Welfare (1987): Decision making
on influenza immunization. The Ministry's announce‑

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to simply define the illnessunder scrutiny ( 1 2). Teachers o洗enraise high fever, headache, Sore throat, appetite loss, vomltlng,

5. National Institute of Infectious Diseases and Infectious

and diarrhea as major common symptoms for ILI in the SHSS,

Diseases Control Division, Minisby of Healthand Welfare

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infections are included in SHSS data. Adenovirus infection

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7. Centers f♭r Disease Control and Prevention (1998):and Norwalk virus infections might have got mixed with theRevising CDC's guide lines f♭r evaluating surveillance

SHSS data, because those diseases also reach epidemic levels
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systems. Morbid. Mortal. Wkly. Rep., 47, 1083･
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is characterized by severe vomltlng, though it lasts only fb∫ aday or two, and diarrheaヮay develop later (16)･ In very young

9. Glezen, W. P. and Cough, 良. B.(1978): Interpandemic

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toms can be the presentlng Symptoms ‑ fever only, fever with

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diarrhea and vomltlng ‑ and could overlap with viral gastro‑

enteritis infections. In order to minimize the non‑influenza

system. Public Health Rep., 94, 88‑92･ll. Lenaway, D. and Ambler, A. (1995): Evaluation ofa
school‑based influenza surveillance system. Public HealthRep., 110, 333‑337･12. Sprenger, M. J., Kempen, B. M., Harmoun, C.and Masurel,cases, a standardized case definition excluding vomltlng anddia汀hea symptoms should be developed fわr schoolchil血en'sILl and assessed.When ILI outbreaks occur in school, besidereporting them to the SHSS, a limited number of nasopharyn‑geal swabs, as well as vomitus or stool specimens, should besubmitted to the local public health laboratories･N. ( 1 992): Electronic influenza surveillance. Lancet, 339,

We found a higher level of sensitivity, specificity, and posi‑874.

tive predictive value in the SHSS than in the ISSS. However,

13. Ohmi, A., Okamoto, M., Chiba, F., Endo, C., Ito, Y.,

it is not yet proven whether these results would be fわundNishimura, H., Nagai, Y. and Katsushima, N. (2001):

during less severe influenza seasons. The SHSS has a disad‑vantage in that data are not available during New Year 's break.

November‑December 2000 ‑ Sen血i City and Yamagata

Isolation of adenoviruses from respiratory infections,Aninfluenza outbreak may not be detected in a timely mannerCity. infect. Agents SuⅣeillance Rep., 22, 33‑34 (in Japa‑if an epidemic starts during the break.

nese).

lt is unknown whether timely class/school closure can14. National Institute of Infectious Diseases and Infectious

minimize influenza epidemics, not only in children, but inDiseases Control Division, Minisby of Healthand Welfare

the general population. The well‑evaluated SHSS data will be(1 999): Outbreaks of viral gastroenteritis, Japan, October
1 9971September 1 999. Infect. Agents Surveillance Rep.,of use for scientifically based decisions. The SHSS provides29I 6. National Institute of Infectious Diseases and Infectious

20, 265'‑266'.

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30