The occurrence of influenza in different climates is shown to be associated with multiple meteorological factors. Incidence of influenza has been reported to increase during rainy seasons in tropical climates and during dry, cold months of winter in temperate climates. This study was designed to explore the role of absolute humidity (AH), relative humidity (RH), temperature, and wind speed (WS) on influenza activity in Toronto area, Ontario, Canada. Environmental data obtained from four meteorological stations in Toronto area, for the period of January 1, 2010 to December 31, 2015, were linked to patient´s influenza data obtained for the same locality and period. Data were analyzed using correlation, negative binomial regressions with linear predictors and splines to capture the non-linear relationship between exposure and outcomes. Our study found a negative association of both AH and temperature with influenza A and B viruses. Effect of RH in influenza A and B was controversial Temperature fluctuation was associated with increased influenza B virus. Influenza virus was less likely to be detected from community patients than those tested as part of an institutional outbreak investigation. This could be more indicative of nosocomial transmission, rather than climactic factors. The non-linear nature of the relation between influenza A virus and temperature and influenza B virus and AH, RH and temperature could explain the complexity and variation between influenza A and B viruses. Predicting influenza activity is important for the timing of disease prevention and control measures as well as for resource allocation.ImportanceThis study examines the relationship between environmental factors on the occurrence of influenza in general. Since seasonality of influenza A and B viruses is different in most temperate climates, we also examined each influenza virus separately. This study reports a negative association of both absolute humidity and temperature with influenza A and B viruses and tries to understand the controversial effect of RH on influenza A and B viruses. This study reports a non-linear relation between influenza A and B viruses with temperature and influenza B virus with absolute and relative humidity. The non-linear nature of these relations could explain the complexity and difference in seasonality between influenza A and B virus, with the latter predominating later in the season. Separating community-based specimens from those obtained during outbreaks was also a novel approach in this research. These findings provide further understanding of influenza transmission in temperate climates.