Wednesday, October 19, 2016

China's Hazy Flu Season: Revisited



Just over 2 months ago, in China's Hazy Flu Season, we looked at speculation that China's deteriorating air quality might be a co-factor in driving the severity of their yearly flu seasons.  Particularly, but not exclusively, at issue were the effects of fine particles less than 2.5 micrometers in diameter (PM2.5).

First we looked at a number of earlier studies that had found an apparent correlation between the level of air pollution, and respiratory outbreaks in China, including: 

Impact of ambient fine particulate matter (PM2.5) exposure on the risk of influenza-like-illness: a time-series analysis in Beijing, China.

PM2.5 in Beijing - temporal pattern and its association with influenza.

We then looked at a letter to the Editor of the American Journal of Infection Control  that not only described the extent of last December's severe flu outbreak in Shanghai, it also discussed its potential link to the Shanghai's poor air quality last winter.

While the evidence is still limited, we've a new study - published in the Journal Environmental International - that provides a bit more weight to the argument.

Environ Int. 2016 Oct 10. pii: S0160-4120(16)30553-0. doi: 10.1016/j.envint.2016.10.004. [Epub ahead of print]

The impact of ambient fine particles on influenza transmission and the modification effects of temperature in China: A multi-city study.

Chen G1, Zhang W2, Li S1, Zhang Y3, Williams G1, Huxley R4, Ren H5, Cao W5, Guo Y6.



There is good evidence that air pollution is a risk factor for adverse respiratory and vascular health outcomes. However, data are limited as to whether ambient fine particles contribute to the transmission of influenza and if so, how the association is modified by weather conditions.


We examined the relationship between ambient PM2.5 and influenza incidence at the national level in China and explored the associations at different temperatures.

Daily data on concentrations of particulate matter with aerodynamic diameter < 2.5μm (PM2.5) and influenza incidence counts were collected in 47 Chinese cities. A Poisson regression model was used to estimate the city-specific PM2.5-influenza association, after controlling for potential confounders. Then, a random-effect meta-analysis was used to pool the effects at national level. In addition, stratified analyses were performed to examine modification effects of ambient temperature.


Ambient PM2.5 may increase the risk of exposure to influenza in China especially on cooler days. Control measures to reduce PM2.5 concentrations could potentially also be of benefit in lowering the risk of exposure and subsequent transmission of influenza in China.

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