title: 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: BACKGROUND
  The 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.
  
  
  METHODS
  We 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.
  
  
  RESULTS
  At 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.
  
  
  CONCLUSIONS
  Annual 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.
authors.affiliation: Department of Virology, Tohoku University Graduate School of Medicine, Sendai, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Kamigaki
authors.affiliation: Department of Virology, Tohoku University Graduate School of Medicine, Sendai, Japan.
authors.forename: Liling
authors.initials: L
authors.lastname: Chaw
authors.affiliation: Department of Epidemiology and Biostatistics, Research Institute for Tropical Medicine, Department of Health, Manila, Philippines.
authors.forename: Alvin G
authors.initials: AG
authors.lastname: Tan
authors.affiliation: Department of Virology, Tohoku University Graduate School of Medicine, Sendai, Japan.
authors.forename: Raita
authors.initials: R
authors.lastname: Tamaki
authors.affiliation: Department of Epidemiology and Biostatistics, Research Institute for Tropical Medicine, Department of Health, Manila, Philippines.
authors.forename: Portia P
authors.initials: PP
authors.lastname: Alday
authors.affiliation: Department of Epidemiology and Biostatistics, Research Institute for Tropical Medicine, Department of Health, Manila, Philippines.
authors.forename: Jenaline B
authors.initials: JB
authors.lastname: Javier
authors.affiliation: Research Institute for Tropical Medicine, Department of Health, Manila, Philippines.
authors.forename: Remigio M
authors.initials: RM
authors.lastname: Olveda
authors.affiliation: Department of Virology, Tohoku University Graduate School of Medicine, Sendai, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Oshitani
authors.affiliation: Department of Epidemiology and Biostatistics, Research Institute for Tropical Medicine, Department of Health, Manila, Philippines.
authors.forename: Veronica L
authors.initials: VL
authors.lastname: Tallo
mesh_terms: D006801:Humans; D006813:Humidity; D007251:Influenza, Human / Q000453:epidemiology*; D007564:Japan / Q000453:epidemiology; D016014:Linear Models; D010679:Philippines / Q000453:epidemiology; D011891:Rain; D018357:Respiratory Syncytial Virus Infections / Q000453:epidemiology*; D012307:Risk Factors; D012621:Seasons; D013696:Temperature; D014329:Tropical Climate; D058067:Wavelet Analysis