Respiratory syncytial virus seasonality in Brazil: implications for the immunisation policy for at-risk populations

Abstract

Respiratory syncytial virus (RSV) infection is the leading cause of hospitalisation for respiratory diseases among children under 5 years old. The aim of this study was to analyse RSV seasonality in the five distinct regions of Brazil using time series analysis (wavelet and Fourier series) of the following indicators: monthly positivity of the immunofluorescence reaction for RSV identified by virologic surveillance system, and rate of hospitalisations per bronchiolitis and pneumonia due to RSV in children under 5 years old (codes CID-10 J12.1, J20.5, J21.0 and J21.9). A total of 12,501 samples with 11.6% positivity for RSV (95% confidence interval 11 - 12.2), varying between 7.1 and 21.4% in the five Brazilian regions, was analysed. A strong trend for annual cycles with a stable stationary pattern in the five regions was identified through wavelet analysis of the indicators. The timing of RSV activity by Fourier analysis was similar between the two indicators analysed and showed regional differences. This study reinforces the importance of adjusting the immunisation period for high risk population with the monoclonal antibody palivizumab taking into account regional differences in seasonality of RSV.

Fig. 1. : time series of the indicator: monthly positivity of samples for respiratory syncytial virus identified by indirect immunofluorescence and divided by the number of monthly valid samples, wavelets (left), and significance spectrum (right) in the five regions of Brazil between 2005-2012. (A) Wavelet power spectra (left): darker areas correspond to higher intensity of the seasonal signal; pink contours show statistically significant areas (alpha = 5%); the red line delimits the region not influenced by the edge effects; the timescale on the left represents the time in years in an algorithmic scale of base 2. (B) Global wavelet spectrum (black line) with a significance limit of alpha = 5% (pink).

Fig. 3. : temporal trend of sample positivity (indirect immunofluorescence) for respiratory syncytial virus, hospitalisation rates for RSV-associated bronchiolitis and pneumonia, and suggested periods for RSV infection prophylaxis with immunobiologicals for the five regions of Brazil. Jointly displays the temporal distribution of the different RSV indicators in the five regions of Brazil. The grey strips indicate the most appropriate periods for immunobiological prophylaxis in each region of the country.

Fig. 2. : time series of the monthly hospitalisation rates in infants under the age of 5 years due to bronchiolitis and pneumonia associated with respiratory syncytial virus (per 100,000 inhabitants), in the wavelet time series (left) and significance spectrum (right) in five regions of Brazil during 2005-2012. (A) Wavelet power spectra (left): darker areas correspond to a higher intensity of the seasonal signal; pink contours show statistically significant areas (alpha = 5%); the red line delimits the region not influenced by the edge effects; the timescale on the left represents the time in years in an algorithmic scale of base 2. (B) Global wavelet spectrum (black line) with a significance limit of alpha = 5% (pink).