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Schools are important foci of influenza transmission and potential targets for surveillance and interventions. Soh, et al. (2012) 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.
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During the initial wave of pandemic H1N1 (pdmH1N1) infections from June to Sept 2009 in Singapore, the researchers collected data on nation-wide laboratory confirmed cases (Sch-LCC) and daily temperature monitoring (Sch-DTM), and teacher-led febrile respiratory illness reporting in six 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 six schools was also investigated through a Bayesian hierarchical model.
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By week 30, for primary and secondary school children respectively, 63 percent and 79 percent of incidence for Sch-LCC had occurred, compared with 50 percent and 52 percent for GP-ILI data, and 48 percent and 53 percent 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 in the six schools. We estimate from serology that 41.8 percent (95% CI: 30.2% to 55.9%) of primary and 43.2 percent of secondary school-aged children were infected. Sch-FRI rates were similar across the six 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.
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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, the researcehrs conclude. Their research was published in BMC Infectious Diseases.Â
Reference: Soh SE, et al. 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. BMC Infectious Diseases 2012, 12:336 doi:10.1186/1471-2334-12-336
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