Seasonality of Respiratory Syncytial Virus Hospitalization.

Seasonality of respiratory syncytial virus (RSV) infection is an area of limited knowledge. In this study, we set out to get insight into the epidemic characteristics of RSV. We retrospectively evaluated medical files of 512 hospitalizations in children due to RSV infection from January 2010 to July 2017. In this cohort of patients, there were 96.3% of children below 1 year of age; the median age was 2.8 months. The influence of weather condition during the week of hospitalization (WH) and also the preceding week (WP) on the rate of hospitalizations was also assessed. An overview of morbidity data demonstrates that the epidemic RSV season started from Week 50 of a year and lasts until Week 15 of the following year, with a peak between Week 4 and Week 10. The average monthly percentage rate of morbidity per year was as follows: December, 12.3%; January, 24.5%; February, 29%; and March, 21.7%. Hospitalizations were positively associated with the minimum and maximum outside air temperature during the WH (62.5% and 59.7%, respectively) and the WP (64.3% and 63.4%, respectively) and with relative humidity (WH 23% and WP 29.8%). A weak association with the wind speed was also noticed (WH 22% and WP 21%), while there was no influence of the level of atmospheric pressure on RSV morbidity. We conclude that seasonality of RSV is present between December and April each year, and morbidity is mostly influenced by minimum-maximum outside air temperature changes. Further epidemiological exploration is required to get a better knowledge on both active and passive immunization against RSV.