Researchers report a global pattern that links influenza outbreaks with absolute humidity and temperature. Patterns of influenza outbreaks differ between temperate and tropical latitudes. In temperate countries, influenza outbreaks are associated with seasonal changes in temperature and absolute humidity. By contrast, seasonal climate fluctuations in tropical countries are minimal, making influenza outbreaks harder to explain with environmental factors. To explore the relationship between the environment and influenza on a global scale, George Sugihara and colleagues used an empirical dynamic modeling framework, an approach that detects causality in nonlinear dynamic systems, to predict influenza outbreaks from environmental drivers, namely absolute humidity, temperature, relative humidity, and precipitation. The authors found that absolute humidity drives influenza across latitudes and that temperature determines whether the association is positive or negative. At low temperatures, high absolute humidity reduces influenza incidence, but high absolute humidity increases the incidence of influenza in the warm tropics. The results suggest that the balance between positive and negative effects of absolute humidity on influenza outbreaks shifts around 70-75°F. Absolute humidity and temperature influence global influenza patterns more strongly than relative humidity and precipitation, and influence influenza incidence at all latitudes regardless of environmental or influenza seasonality. According to the authors, the results offer a unified explanation for how environmental drivers influence global influenza outbreaks. - Read at PNAS.org
Article #16-07747: “Global environmental drivers of influenza,” by Ethan R. Deyle, M. Cyrus Maher, Ryan Hernandez, Sanjay Basu, and George Sugihara.