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Open Access Research article

Teacher led school-based surveillance can allow accurate tracking of emerging infectious diseases - evidence from serial cross-sectional surveys of febrile respiratory illness during the H1N1 2009 influenza pandemic in Singapore

Shu E Soh1, Alex R Cook1, Mark IC Chen1239*, Vernon J Lee14, Jeffery L Cutter5, Vincent TK Chow1, Nancy WS Tee6, Raymond TP Lin5, Wei-Yen Lim1, Ian G Barr7, Cui Lin5, Meng Chee Phoon1, Li Wei Ang5, Sunil K Sethi8, Chia Yin Chong6, Lee Gan Goh8, Denise LM Goh8, Paul A Tambyah8, Koh Cheng Thoon6, Yee Sin Leo29 and Seang Mei Saw1

Author Affiliations

1 National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077, Singapore

2 Communicable Disease Centre, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore 308433, Singapore

3 Duke-NUS Graduate Medical School, 8 College Road, Singapore, 169857, Singapore

4 Ministry of Defence, Gombak Drive, Singapore, 669645, Singapore

5 Ministry of Health, College of Medicine Building, 16 College Road, Singapore, 169854, Singapore

6 KK Women’s and Children’s Hospital, 100 Bukit Timah Road, Singapore, 229899, Singapore

7 World Health Organization Collaborating Centre for Reference and Research on Influenza, 10 Wreckyn Street, North Melbourne, VIC, 3051, Australia

8 National University Health Systems, 1E Kent Ridge Road, Singapore, 119228, Singapore

9 Department of Clinical Epidemiology, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore, 308433, Singapore

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BMC Infectious Diseases 2012, 12:336  doi:10.1186/1471-2334-12-336

Published: 4 December 2012

Abstract

Background

Schools are important foci of influenza transmission and potential targets for surveillance and interventions. We compared several school-based influenza monitoring systems with clinic-based influenza-like illness (ILI) surveillance, and assessed the variation in illness rates between and within schools.

Methods

During the initial wave of pandemic H1N1 (pdmH1N1) infections from June to Sept 2009 in Singapore, we collected data on nation-wide laboratory confirmed cases (Sch-LCC) and daily temperature monitoring (Sch-DTM), and teacher-led febrile respiratory illness reporting in 6 sentinel schools (Sch-FRI). Comparisons were made against age-stratified clinic-based influenza-like illness (ILI) data from 23 primary care clinics (GP-ILI) and proportions of ILI testing positive for pdmH1N1 (Lab-ILI) by computing the fraction of cumulative incidence occurring by epidemiological week 30 (when GP-ILI incidence peaked); and cumulative incidence rates between school-based indicators and sero-epidemiological pdmH1N1 incidence (estimated from changes in prevalence of A/California/7/2009 H1N1 hemagglutination inhibition titers ≥ 40 between pre-epidemic and post-epidemic sera). Variation in Sch-FRI rates in the 6 schools was also investigated through a Bayesian hierarchical model.

Results

By week 30, for primary and secondary school children respectively, 63% and 79% of incidence for Sch-LCC had occurred, compared with 50% and 52% for GP-ILI data, and 48% and 53% for Sch-FRI. There were 1,187 notified cases and 7,588 episodes in the Sch-LCC and Sch-DTM systems; given school enrollment of 485,723 children, this represented 0.24 cases and 1.6 episodes per 100 children respectively. Mean Sch-FRI rate was 28.8 per 100 children (95% CI: 27.7 to 29.9) in the 6 schools. We estimate from serology that 41.8% (95% CI: 30.2% to 55.9%) of primary and 43.2% (95% CI: 28.2% to 60.8%) of secondary school-aged children were infected. Sch-FRI rates were similar across the 6 schools (23 to 34 episodes per 100 children), but there was widespread variation by classrooms; in the hierarchical model, omitting age and school effects was inconsequential but neglecting classroom level effects led to highly significant reductions in goodness of fit.

Conclusions

Epidemic curves from Sch-FRI were comparable to GP-ILI data, and Sch-FRI detected substantially more infections than Sch-LCC and Sch-DTM. Variability in classroom attack rates suggests localized class-room transmission.

Keywords:
Respiratory tract infections; Vaccination; Serology