PerspectiveInfectious Diseases

Metropolitan versus small-town influenza

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Science  05 Oct 2018:
Vol. 362, Issue 6410, pp. 29-30
DOI: 10.1126/science.aav1003

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Every year, influenza epidemics occur during winter in regions with temperate climates. The duration, size, and precise timing of influenza epidemics vary from season to season—the numbers of hospitalizations and deaths can be substantial. The influenza epidemic in the winter of 2017–2018 in the United States was extraordinarily severe and long, straining the health care system capacity. Various external factors have been proposed to explain the duration, size, and precise timing of seasonal influenza epidemics, including weakened immune systems during winter, increased social crowding indoors, school leave during the Christmas holiday, and the lower humidity in winter. Inferring the relative importance of each of those factors is difficult because they act on a dynamic process that responds sensitively to changes and that is only observable with a measure of error (14). How can we determine what is driving influenza epidemics? On page 75 of this issue, Dalziel et al. (5) demonstrate how influenza epidemics in a city are driven by fluctuations in humidity, modulated by the population size. This implies that influenza control measures could work differently in large metropolitan areas compared to small towns.