Jpn. J. Infect. Dis., 55, 2002

Laboratory and Epidemiology Communications

Evaluation of the School Health Surveillance Systemfor Influenza, Tokyo, 1999-2000
Hayato Fujii1,5*, Hiroshi Takahashi2, Takaaki Ohyama2,
Kinuyo Hattori3 and Shigeto Suzuki3,4
12

Field Epidemiology Training Program andInfectious Disease Surveillance Center, National Institute of Infectious Diseases,
Toyama 1-23-1, Shinjuku-ku, Tokyo 162-8640,
3Tokyo Metropolitan Research Laboratory and Public Health,
Hyakunin-cho 3-24-1, Shinjuku-ku, Tokyo 169-1173,
4
Reimeikai-Minamidai Hospital,
Ogawa-machi 1-485, Kodaira-shi, Tokyo 187-0032 and5Community Medicine Section, Public Health and Welfare Bureau,
Kamihonnoujimae-cho 488, Teramachi Oike, Nakagyo-ku, Kyoto 604-8571
Communicated by Kunihiko Masukawa(Accepted July 23, 2002)
Gargle and blood specimens were also collected fromschoolchildren with ILI during the study period. We used thegargled water for virus isolation in Madin-Darby canine kidney(MDCK) cells and identification by specific neutralizing antiinfluenza ferret sera (provided by the National Institute ofInfectious Diseases, Tokyo). Virus, once isolated from gargled
water, was subjected to reverse transcriptase polymerase chain
reaction (RT-PCR) in order to detect the virus genome. Virus
diagnosis was done by either neutralization or RT-PCR or by
the both. For paired blood specimens of absentee children,
we performed the complement fixation test to determine if
antibody titer increased over fourfold, which we judged aspositive.
Figure 1 compares the SHSS and the ISSS data during theobservation period. Similar trends were observed for SHSSand ISSS. The epidemic status was observed from the 3rd
week through the 6th week of the new year.
The PVP data for the gargle and blood specimens are shownin Table 1. The acceptable PVP for the gargle specimens wasobtained during the 51st week in the previous year through the6th week of the new year. The acceptable PVP was obtained
only on the 2nd and 3rd weeks for the blood specimens.
According to the report by the Tokyo Metropolitan ResearchLaboratory and Public Health (3), the magnitude of influenza
epidemic was rather larger than usual in Tokyo in the 1999/
2000 season. The average of the cumulative number of influenza patients per sentinel site in 1999/2000 was over 20. There
was a peak in the 3rd-5th weeks as usual. A major epidemic
of influenza type A was seen. The ratio H1N1: H3N2 was
2.4:1 in the 4-15 age group, and the ratio was 1:3 in those
aged over 16. Peaks of H3N2 and H1N1 were observed in
5th and 4th-7th weeks, respectively.

The school health surveillance system (SHSS) is the sole
notifiable surveillance system in Japan for indicating thepresence of pediatric influenza (1). To measure the magnitudeof influenza among schoolchildren in all 47 prefectures, theMinistry of Education, Science, Sports and Culture and theMinistry of Health, Labour and Welfare have jointly run theSHSS since the school health law was enacted in 1958. Here,the schools are asked to report number of absentees with
influenza-like illness (ILI) when it had school/class closure.
Principal of the school can decide the closure, usually for 24 days, if absentees reached above 20% of students.
By comparing the SHSS data with the national sentinel
surveillance system for influenza (ISSS) data, we found that
the SHSS had levels of sensitivity, specificity, and predictive
value positive (PVP) comparable to those of the ISSS (2).
However, as this study was based upon only the national
sentinel surveillance data during the 2nd through 11th weekof 1998 and 1999 for all prefectures in Japan, trends inspecific regions in Japan under a longer time frame could not
be assessed.
In the present analysis, SHSS and ISSS data were compared
for the age group 4-14 years during the 49th week of 1999
through the 13th week of 2000 (except for winter vacationfrom 52nd of 1999 to 1st week of 2000). Tokyo had 36 pediatricsentinel sites reporting influenza cases weekly on a regularbasis. Ten percent of the patients in such sites were regularly
checked for influenza virus in their throat lavage (virologicaltesting done by the Tokyo Metropolitan Research Laboratory
and Public Health, Tokyo).
*Corresponding author: Tel: +81-75-222-3421, Fax: +81-75-2223416, E-mail: fujiih@jmail.plala.or.jp
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Jpn. J. Infect. Dis., 55, 2002

Fig. 1. Comparison of the SHSS and ISSS data, Tokyo, 2000
SHSS: school health surveillance system
ISSS: national sentinel surveillance system for influenza
ILI: influenza-like illness

Table 1. PVP for gargled water and blood specimens compared with the ISSS and SHSS data, Tokyo, 1999-2000 season
49th

50th

51st

52nd

1st

2nd

3rd

4th

5th

6th

Number of ILI children/36 sentinel site

3686

191

118

173

337

1,364

2,101

2,065

1,237

Classification by type in a part of ISSS data*
A(H3N2)A(H1N1)
B

1
0
0

0
201
10020

700

112
1

8
40

9
70

8
200

3
90

Number of absent school children with ILI/100,000

22204

303––

60

2,969

5,885

6,650

2,8690(0/4)
0(0/4)

6.7(1/15)
25.0(1/4)

75.0(6/8)
33.3(1/3)––––

75.0(3/4)
75.0(3/4)

73.2(41/56)
69.0(20/29)

85.7(24/28)
61.9(13/21)

66.7(2/3)
42.9
(3/7)

100(4/4)
25.0(1/4)

0000
10240

–
––––
–

3001
400

0
240

2000
40

Week

PVP for specimen (%)
Gargled water
Blood
Classification by type in SHSS
A(H3N2)A(H1N1)
B

PVP: predictive value positive, ISSS: national sentinel surveillance system for influenza,
SHSS: school health surveillance system, ILI: influenza like illness.
Week 52nd and 1st: winter break.
*Laboratory data were collected as a pathological surveillance in a part of ISSS.

surveillance systems” (H13-Shinko-5).

Of a total of 81 influenza virus-positive gargle specimens(either by isolation or RT-PCR), 73 (90.1%) were type A(H1N1), and 8 (9.9%) type A (H3N2). No other type wasdetected. Of 50 virus isolation-positive gargle specimens, 42(84%) were type A (H1N1), and 8 (16%) type A (H3N2).
Influenza consistently occurs among school-aged children,
followed by spread among family members (4). Both theSHSS and ISSS data showed a consistent rise from the 49thweek. As the observed populations in both systems are fromthe same age group, the majority of ILI patients in both SHSSand ISSS are absentees in class closures. This suggests thatthe epidemic trend among school-aged children can be easily
assessed by SHSS alone (without requiring ISSS).

REFERENCES
1. Reichert, T. A., Sugaya, N., Fedson, D. S., Glezen, W. P.,
Simonsen, L. and Tashiro, M. (2001): The Japaneseexperience with vaccinating schoolchildren against influenza. N. Eng. J. Med., 344, 889-896.
2. Takahashi, H., Fujii, H., Shindo, N. and Taniguchi, K.
(2001): Evaluation of the Japanese school health surveillance system for influenza. Jpn. J. Infect. Dis., 54, 2730.
3. Tokyo Metropolitan Research Laboratory and Public
Health (2000): Infectious diseases surveillance 1999/
2000. The Seventh Report of Influenza Virus laboratory
Data. 31 March 2000 (in Japanese).
4. Lenaway, D. and Ambler, A. (1995): Evaluation of aThis study was planned and developed under support of aJapanese Ministry of Health, Labour and Welfare scientificresearch grant on “coordination for the national and prefectural
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school-based influenza surveillance system. Public HealthRep., 94, 88-92.
5. Glezen, W. P. (1998): Influenza viruses. p. 2024-2041.

In R. D. Feigin and J. D. Cherry (eds.), Textbook ofPediatric Infectious Diseases. 4th ed. W. B. Saunders Co.,
Philadelphia.

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