Abstract
Increased social contact within school settings is thought to be an important factor in seasonal outbreaks of acute respiratory infection (ARI). To better understand the degree of impact, we analysed electronic health records and compared risks of respiratory infections within communities while schools were in session and out-of-session. A time series analysis of weekly respiratory infection diagnoses from 28 family medicine clinics in Wisconsin showed that people under the age of 65 experienced an increased risk of ARI when schools were in session. For children aged 5-17 years, the risk ratio for the first week of a school session was 1.12 (95% confidence interval (CI) 0.93-1.34), the second week of a session was 1.39 (95% CI 1.15-1.68) and more than 2 weeks into a session was 1.43 (95% CI 1.20-1.71). Less significant increased risk ratios were also observed in young children (0-4 years) and adults (18-64 years). These results were obtained after modelling for baseline seasonal variations in disease prevalence and controlling for short-term changes in ambient temperature and relative humidity. Understanding the mechanisms of seasonality make it easier to predict outbreaks and launch timely public health interventions.
Highlights
Acute respiratory infection (ARI) seasonality is generally believed to stem from three main factors: the cyclical nature of host immunity, weather variations and changes in host behaviour, most notably in how people interact with each other [1, 2]
Once annual seasonality was modelled, neither temperature nor relative humidity was significantly associated with additional risk of infection (P > 0.05 in all age groups). These findings suggest that longer-term seasonal patterns are the predominant factors influencing disease activity and that these seasonal differences cannot be explained by short-term changes in temperature and/or relative humidity
This study showed that the start of school sessions plays a significant role in seasonal outbreaks by increasing the risk of all-cause, medically attended ARIs
Summary
Acute respiratory infection (ARI) seasonality is generally believed to stem from three main factors: the cyclical nature of host immunity, weather variations and changes in host behaviour, most notably in how people interact with each other [1, 2]. Close person-to-person contact, among school-age children, is frequently cited as an important example of the latter. Measles was one of the first viruses that showed a strong correlation with school sessions [2, 4, 5]. More recent research on influenza [6, 7] has suggested a link, and rhinovirus has demonstrated autumnal peaks that correlate closely with the onset of school [8]. Any attempt to discern a correlation between school attendance and seasonality, is necessarily complicated by other potential drivers that these studies do not address
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