Seasonality of Influenza and Respiratory Syncytial Viruses and the Effect of Climate Factors in Subtropical–Tropical Asia Using Influenza-Like Illness Surveillance Data, 2010 –2012

Abstract

IntroductionThe seasonality of influenza and respiratory syncytial virus (RSV) is well known, and many analyses have been conducted in temperate countries; however, this is still not well understood in tropical countries. Previous studies suggest that climate factors are involved in the seasonality of these viruses. However, the extent of the effect of each climate variable is yet to be defined.Materials and MethodsWe investigated the pattern of seasonality and the effect of climate variables on influenza and RSV at three sites of different latitudes: the Eastern Visayas region and Baguio City in the Philippines, and Okinawa Prefecture in Japan. Wavelet analysis and the dynamic linear regression model were applied. Climate variables used in the analysis included mean temperature, relative and specific humidity, precipitation, and number of rainy days. The Akaike Information Criterion estimated in each model was used to test the improvement of fit in comparison with the baseline model.ResultsAt all three study sites, annual seasonal peaks were observed in influenza A and RSV; peaks were unclear for influenza B. Ranges of climate variables at the two Philippine sites were narrower and mean variables were significantly different among the three sites. Whereas all climate variables except the number of rainy days improved model fit to the local trend model, their contributions were modest. Mean temperature and specific humidity were positively associated with influenza and RSV at the Philippine sites and negatively associated with influenza A in Okinawa. Precipitation also improved model fit for influenza and RSV at both Philippine sites, except for the influenza A model in the Eastern Visayas.ConclusionsAnnual seasonal peaks were observed for influenza A and RSV but were less clear for influenza B at all three study sites. Including additional data from subsequent more years would help to ascertain these findings. Annual amplitude and variation in climate variables are more important than their absolute values for determining their effect on the seasonality of influenza and RSV.

Identification of viral etiology of acute respiratory tract infections in children and adults in Tabanan, Bali, Indonesia

“…In our study, 16 (8.0 %) patients were RSV-positive and more frequently in children under 5 years old (n=15, 7.5 %). Although RSV outbreaks are known to vary from year to year according to geographical pattern, majority of RSV infection in this study was observed in March during the height of the rainy season which is consistent with earlier studies in tropical countries [24,25].…”

Influenza in temperate and tropical Asia: a review of epidemiology and vaccinology

“…Differences in the epidemiology of influenza viruses are also evident, and outbreaks of different influenza types/ subtypes are not always synchronous. 7,17 For example, influenza A/H3N2 has been reported to cause shorter but more intense and more frequent epidemics than influenza A/H1N1 and B/Yamagata, perhaps reflecting differences in the rate of antigenic drift. 18 The stability of the currently observed pattern may also be affected by climate change, and predictions that the climates across much of Asia will become warmer and wetter may have important implications for influenza virus activity.…”

“…This reflects the range of climates, from the equatorial South to an almost polar North. 7 Recent reports that clinical protection wanes in the weeks after influenza vaccination emphasize the importance of optimally timing vaccination to local epidemiology. 8 It also raises questions as to whether influenza vaccines should be administered more frequently than annually and what may be the benefits in Asia of access to new vaccines with enhanced immunogenicity and effectiveness.…”

Pneumonia: A Challenging Health Concern with the Climate Change

“…Studies in Hong Kong [27] and China [28], respectively support the impact of the changing weather pattern on the magnitude of respiratory infection and the seeking of emergency healthcare. The pattern of seasonality on viral respiratory infections has clearly been reported in temperate countries, but data from tropical regions are sparse [29]. The vulnerability of children under the tropics could be emphasized by poverty-related conditions such as malnutrition and helminth infections as well as poor access to healthcare facilities.…”