Pediatric population size is associated with geographic patterns of acute respiratory infections among adults

Study objectives: We measure the association between proportion of children and specific pediatric age groups in a local population with the timing and rate of adult emergency department (ED) utilization for influenza and other acute respiratory infections. Methods: We performed an ecologic study on a time-series of adult patients presenting to Massachusetts EDs and residing in the greater Boston area from October 1, 2001, to September 30, 2005. Patients presenting with acute respiratory infection, used as a marker for influenza, were aggregated by home address ZIP code. We measured geographic patterns of timing and rate of adult respiratory infection-related ED utilization. We performed correlation analysis of rates and peaks identified in this analysis with pediatric population data from the US census (including specific pediatric age groups) by Poisson regression. Results: One hundred fifty seven thousand five hundred forty two adult respiratory infection-related ED visits (30 visits per 1,000 adults per year) were analyzed. Visits were distributed across 55 of ZIP codes, in which proportions of children (aged 0 to 18 years) ranged from 2.7% to 34.9% in these communities. Proportion of children in a ZIP code was directly associated with timing of seasonal onset of acute respiratory infections among adults (univariate Poisson regression rate ratio [RR] 0.985; 95% confidence interval [Cl] 0.977 to 0.993). The proportion of children also explained the patterns of adult acute respiratory infection-related ED utilization rates (RR 1.035; 95% Cl 1.024 to 1.047). Three- to 4-year-olds were found to be the most significant predictors of adult illness rate (RR 1.380; 95% Cl 1.238 to 1.539) and timing of onset (RR 0.881; 95% Cl 0.816 to 0.952). Conclusion: We demonstrate a positive correlation between the timing and rate of ED utilization by adults and the proportion of children in the population. These findings add to a growing body of evidence supporting a critical role played by children in community-wide transmission of acute respiratory infections.