While absolute humidity drives influenza across latitudes, temperature modulates the effect
With winter approaching, India has already experienced the outbreak of bird flu. Thousands of birds are being culled in Kerala and zoos in different states have been shut down. But this is not a phenomenon unique to cold weather as avian influenza outbreaks affect even those living in warm and tropical regions.
It is this lack of a seasonal connection between flu outbreaks in tropical and temperate climates that makes it challenging to study environmental factors that drive the flu.
In a new study conducted by the researchers at the University of California San Diego, it has been observed that humidity is the key link to flu outbreaks around the world and temperature mediates this effect.
What explains the wintertime occurrence of seasonal influenza outbreaks?
Findings of the study published in the journal Proceedings of the National Academy of Sciences suggest that viral shedding by the hosts increases at low temperature with laboratory evidence indicating that absolute humidity decides the transmission of airborne influenza.
The scientists analysed nearly 20 years of global influenza data from the World Health Organization's Global Health Atlas to establish a relation between flu outbreaks, absolute humidity (amount of moisture in the air) and temperature across all latitudes.
The study, led by Scripps postdoctoral researcher Ethan Deyle, arrived at a temperature window of 70-75 degrees Fahrenheit (21-24 degree Celsius). Humidity levels above and below the temperature window become a key factor in the spread of the virus.
While absolute humidity drives influenza across latitudes, temperature modulates the effect. At low temperatures, absolute humidity negatively affects influenza incidence, which means drier conditions ensure survival of the influenza virus when the weather is cold. However, at high temperatures, absolute humidity positively affects influenza, which means wetter conditions improve the survival of virus when it is warm.
The analysis brought to the fore the fact that both temperature and humidity were driving influenza. According to the researchers, this study could “set the stage for public health initiatives such as placing humidifiers in schools and hospitals during cold, dry, temperate winters and in the tropics, perhaps using dehumidifiers or air conditioners set above 75° F to dry air in public buildings".
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The study established a relation between flu outbreaks, absolute humidity and temperature across all latitudes. Credit: Kashif Mardani / Flicker.png)
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