Variation of respiratory syncytial virus and the relation with meteorological factors in different winter seasons.

BACKGROUND Respiratory syncytial virus (RSV) is the most important viral agent causing severe respiratory disease in infants and children. In temperate climates, RSV activity typically peaks during winter. We have described the seasonal variation in RSV activity and investigated which meteorological variables are related to RSV outbreaks for different time lags. METHODS Eleven laboratories in the Netherlands collected data on RSV during the period 1998-2005. Meteorological data were obtained from the Royal Netherlands Meteorological Institute. General linear methods were used to determine the relative contribution of meteorological conditions to reported RSV cases in the winter period. Time lags up to 4 weeks were included to assess a possible delayed weather effect in relation to RSV activity. RESULTS Onset of RSV activity occurred around week 44 and activity peaked around week 52. Timing of peak activity was very consistent over the study period. Relative humidity was positively associated with RSV activity for all time lags, indicating more RSV when relative humidity increased. Minimum temperature was negatively associated with RSV activity and cloud cover was positively related with RSV activity. Interaction (P < 0.06) between minimum temperature and relative humidity was observed for a lag of 0, 1, and 2 weeks, indicating that the combination of low temperature and high humidity contributes more to RSV activity than temperature and humidity alone. CONCLUSIONS Relative humidity, minimum temperature, and cloud cover are important predictors of RSV activity in the Netherlands, with the effect of relative humidity being most consistent.