The importance of the local environment in the transmission of respiratory syncytial virus

The role of the environment in the spread of respiratory infections is poorly understood, and consequently probably underappreciated. To improve our understanding of the environmental drivers of respiratory syncytial virus (RSV) transmission, we examined RSV seasonality in two settings with unusual seasonal patterns: The Gambia (where RSV epidemics occur at different times of the year) and Southeast Florida (where RSV seasonality differs from the rest of mainland USA). We used published data to correlate the seasonality of RSV with rainfall and child nutrition in the Gambia, and with rainfall and temperature in Florida. In the Gambia, RSV incidence was more strongly and more consistently correlated with child nutrition (r = -0.73 [95%CI -0.90 to -0.38]) than with rainfall (r = 0.37 [95%CI 0.20 to 0.52]). In Southeast Florida RSV incidence was strongly correlated with rainfall two months previously (r = 0.65 [95%CI 0.40 to 0.81]) compared to North Florida where RSV incidence was strongly correlated with temperature (r = -0.75 [95%CI -0.87 to -0.56]). We propose that nutrition is the dominant environmental driver of RSV seasonality in the Gambia, while rainfall is the dominant driver of RSV seasonality in Southeast Florida. This reinforces the importance of an ecological scale understanding of disease transmission: only with such an evidence base can setting-specific recommendations be made for public health interventions that are targeted for maximum efficacy.