Correlations between climate factors and incidence--a contributor to RSV seasonality

Respiratory syncytial virus is the most common respiratory virus infection in early childhood, causing a wide range of illness from mild colds to life-threatening croup, bronchiolitis and pneumonia that may require intensive care. Exactly which parameters contribute to the seasonality of RSV (and other respiratory viruses, such as influenza) and their comparative significance are the subject of ongoing intensive debate. This review article summarises the specific contributions and correlations between the incidence of RSV and various climate parameters. This systematic review of the literature specifically focuses on these climate associations and have been stratified by study site latitudes: tropical (0-23.5°N or S), subtropical (23.5-40°N or S) and temperate latitudes (>40°N or S). Correlations between RSV incidence and temperature and relative humidity are particularly variable and inconsistent amongst the tropical regions. In subtropical and temperate regions, RSV incidence is more consistently positively correlated with lower temperatures and higher relative humidity. Although there is some variation with the diagnostic methods used in these studies, most used immunofluorescent viral antigen testing to diagnose RSV infection. Statistically, most studies used some form of regression analysis, which assumes no dependence between data taken at different time points. A few used the autoregressive integrated moving average approach, which may be more realistic for an infectious agent as the total number of cases usually evolves in a time-dependent manner during a typical seasonal epidemic.