Seasonal variability of respiratory syncytial virus infection in the Top End of the Northern Territory (2012-2014).

Aim: To determine the prevalence of respiratory syncytial virus (RSV) in the Top End of the Northern Territory and investigate potential drivers of seasonality including rainfall and humidex (humidity and heat index).

Methods: We performed a retrospective audit of laboratory confirmed cases of RSV from January 2012 to August 2014. Demographic details including age, sex and ethnicity were examined. RSV cases were correlated with monthly rainfall and humidex.

Results: There were 272 positive isolates detected from 4305 clinical samples (positivity rate 6.3%). The majority of cases occurred in children <12 months (n = 151, 55.5%), with a higher burden of disease seen in Indigenous compared to non-Indigenous infants in this age category (P < 0.005). The prevalence of RSV in the 0-5 years age category was 58/10 000 children per annum. Indigenous patients had higher prevalence rates (88.8/10 000 population per annum) and younger onset of infection (7.5 months; Interquartile range (IQR) 3-19 months compared to 13 months for non-Indigenous children; IQR 5 months to 2.4 years). RSV cases correlated most strongly with rainfall in the preceding month (r = 0.72).

Conclusions: The Top End of the Northern Territory has a distinct RSV season that correlates with rainfall and humidex, which differs from Southern Australian disease patterns.