Respiratory syncytial virus (RSV) infections may lead to severe respiratory diseases, particularly in infants and young children. Prophylactic anti-RSV monoclonal antibodies are recommended in high-risk infants. In order to determine the timing of prophylaxis, theseasonal variations of RSV had to be determined. In the present study, we report the climate-related results of an epidemiological study conducted in 32 hospitals of Turkey between May 2008 and September 2010 on children less than two years of age hospitalized with the diagnosis of lower respiratory tract infection (LRTI). We also evaluated the correlations of meteorological variables (average monthly temperature, relative humidity and rainfall) with the percentage of RSV positivity among children hospitalized with a LRTI in Turkey as a whole, as well as among the geographic regions. Children who had used palivizumab against RSV infection and the cases in which respiratory samples could not be collected within 24 hours after hospitalization or 24 hours after emergency room (ER) or outpatient clinic administration were excluded from the study. RSV Respi-strip test kits were used to detect RSV in nasal-washing samples, nasopharyngeal aspirates, and in nasal and nasopharyngeal swabs. During the study period, 3464 children (61.9% boys), with a mean age of 6.4 months, were evaluated. According to age groups, most of the children (37.5%) were between 0-3 months old. RSV positivity was 16.9% (585 patients) in all samples. The highest RSV positivity rate was among children aged 0-3 months (27.4%; p<0.01). When Turkey was evaluated as a whole, RSV peaks were in January and March, in the first and second years of the study, respectively. RSV activity had a biennial pattern; an early season with a strong RSV activity was followed by a late season with a weak RSV activity. RSV was positively correlated with relative humidity (p<0.001, R=0.627) and rainfall (p=0.001, R=0.572), and was negatively correlated with temperature (p<0.001, R=-0.778). In the analysis of the correlation between meteorological variables and RSV positivity by region, there was a significant positive correlation between RSV positivity and relative humidity and a significant negative correlation between RSV positivity and temperature in the four regions evaluated. However, rainfall was positively correlated with RSV activity in all regions, except in the Black Sea and East Anatolian regions. The current study shows the seasonal variation of RSV infections in Turkey in two consecutive years. We believe that a viral surveillance system is required in all countries to detect the activity of respiratory viruses and to implement health care strategies.

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