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.
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.
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.
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.
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