Shift in the timing of respiratory syncytial virus circulation in a subtropical megalopolis: Implications for immunoprophylaxis

Abstract

Respiratory syncytial virus (RSV) is the most common cause of severe respiratory infections worldwide, and an important cause of childhood bronchiolitis, pneumonia and mortality. Although prevention of RSV infection by immunoprophylaxis with palivizumab has proved effective, a precise understanding of the timing of RSV outbreaks is necessary to ensure that infants are protected when RSV is circulating. In this study a consistent shift in the seasonal patterns of RSV circulation in southeast Brazil (Sao Paulo) is reported based on the analysis of 15 years of viral surveillance. Surveillance was conducted from 1996 to 2010 and involved the collection of samples from children with symptoms of acute respiratory infection. Putative changes in school terms, in the proportion of RSV genotypes infecting children and in the seasonal dynamics of several climatic parameters during the period were also investigated. The results revealed a progression in the timing of RSV seasons, with a shift in the onset and peak of RSV epidemics from 2007 onwards. Although lower rainfall and temperatures were associated with the onset of outbreaks, there was no evidence of changes in climate, school terms or in the relative proportion of genotypes in the period analyzed. These findings have direct implications for improving the prophylactic use of palivizumab, and stress the importance of fine tuning prophylaxis with recent surveillance data. In the case of Sao Paulo, palivizumab prophylaxis should be initiated earlier than suggested currently. Similar adjustments may be necessary in other regions.

Environmental Drivers of the Spatiotemporal Dynamics of Respiratory Syncytial Virus in the United States

“…Climate change, in particular an increase in average annual temperature, has been hypothesized to be responsible for shortening the RSV season in England [17] . However, a shift towards earlier RSV epidemics has also been observed in São Paulo, Brazil, which cannot be attributed to changes in climate [13] . A similar shift towards later epidemics has been noted elsewhere [45] .…”

“…Most studies have found a significant association between temperature and RSV activity using time series correlation; however, the direction of the association is not consistent across studies, and such studies do not control for the temporal dependence among observations. RSV activity tends to occur in the coldest months in temperate regions where winter outbreaks are common [6] , [13] , [18] – [20] , [22] , [42] and in the warmest months in subtropical and tropical climates [16] , [25] . Low absolute humidity (proportional to vapor pressure) has been found to be an important correlate of RSV activity in Spain [20] .…”

“…Changes in the birth rate in California (which tended to be larger than within other states) may help to explain why epidemics in this state transitioned from biennial during the 1990s to annual during the 2000s; however, more work is needed to understand how variation in birth rates and transmission rates may impact RSV dynamics. Increased contact rates among older siblings during school terms have also been hypothesized to play an important role in determining RSV seasonality [13] , [46] , and have been shown to play in important role for other respiratory infections [47] – [49] . However, we found that incorporating school-term forcing did not improve the fit of our model to the data ( S1 Text , S6 Table ).…”

“…Attempts have been made to correlate RSV seasonality with climatic variables [13] , [15] – [25] . Such phenomenological analyses are important; however, RSV epidemics show strong signatures of nonlinear epidemic dynamics [26] – [29] and few studies have explored climatic associations in a variety of locations covering a range of RSV seasonality patterns and climatic regimes [25] .…”

Meteorological factors and respiratory syncytial virus seasonality in subtropical Australia

“…Studies from subtropical climates in South America and China report an association with relatively low temperatures; however, this was not apparent in our study. This may be because the average minimum temperature on the Gold Coast does not fall as low as temperatures in these other sites [29][30][31][32][33][34]. One review of cities with similar climates found RSV activity peaked in cities when the mean temperatures were about 1-14°C in the coldest months, which is colder than the Gold Coast winter [7].…”