Thursday, August 04, 2016

China's Hazy Flu Season

12/7/15 - Credit NASA Earth Observatory


Eastern China has long been described as the `cradle of influenza' (see Viral Reassortants: Rocking The Cradle Of Influenza), mainly because human, avian, and swine influenza viruses circulate there more-or-less year round, population densities are very high, and because humans and farm animals there often have opportunities to come in close contact.

In 2013, just two weeks before we first learned about the newly emerging H7N9 virus, in EID Journal: Predicting Hotspots for Influenza Virus Reassortment, we looked at a study that identified 6 key geographic regions where reassortments are likely to emerge.

And high on that list (you guessed it), is Eastern mainland China.

In 2013, in addition to H7N9, China reported a new lineage of H7N7 (see Nature: Genesis Of The H7N9 Virus), and a never-seen-in-humans before H10N8 virus (see HK CHP Notified Of Fatal H10N8 Infection In Jiangxi). 

In 2014 two new viruses - H5N8 and H5N6 - emerged from China, with the former spreading rapidly to Korea, Europe, Taiwan, and North America and the latter continuing to crop up in China, Vietnam, and Laos.

Add in a long history with H5N1, H9N2, and SARS - and the strong suspicion that 2 of the 3 major influenza pandemics (1957 Asian Flu, 1968 Hong Kong Flu) of the last century originated from this region - and you begin to understand why we watch respiratory outbreaks in China so carefully. 

Doing a terrific job of tracking all of this has been Sharon Sanders and the newshounds on FluTrackers, whose forum China - Pneumonia, Respiratory, and Influenza Like Illnesses (ILI), contains hundreds of translated media reports.  

In recent years China's deteriorating air quality has increasingly been suggested as a potential co-factor driving the severity of their yearly flu seasons. Particularly, but not exclusively,  the effects of fine particles less than 2.5 micrometers in diameter (PM2.5).

There have already been number of studies that have 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.

But notably, the age groups most affected by heavy PM2.5  vary by study, and in many cases only ILI rates - not lab confirmed influenza - were studied.  There is, quite frankly, a lot we still don't know about how the environment affects influenza.

Last winter - between November and December - much of the Eastern seaboard of China was once again plagued by heavy and persistent haze and smog (see photo at top of blog).   
At the same time, we were seeing reports of extremely heavy pediatric respiratory outbreaks, including this one from FluTrackers (China - Surge in pediatric respiratory outpatients in Shanghai - weather and smog blamed - December 9, 2015).

Dozens of similar reports came in from Anhui province, Jiangsu Province, and Liaoning Province (among others)

Today we've a letter to the Editor of the American Journal of Infection Control  that not only describes the extent of the outbreak in Shanghai last December, it also discusses its potential link to the Shanghai's poor air quality last winter.

It makes for an interesting read, particularly for those who followed last year's flu reports out of China.  I've only included an excerpt, so follow the link to read:

Haze and influenza A virus: Coincidence or causation?
Pan, QingchunTang, ZhenghaoYu, YongshengXi, MinZang, Guoqing et al.

American Journal of Infection Control , Volume 44 , Issue 8 , 959 - 960


The epidemiologic association between the occurrence of haze and the incidence of influenza A virus infection remains largely unknown.5 However, during the widespread and dense haze events that occurred during the winters of both 2013 and 2015, we observed a sharp increase in the number of patients with respiratory tract infection, especially influenza A virus infections. 

Therefore, it is important to understand whether a relationship exists between the occurrence of haze and the risk of influenza A virus infection. A number of important questions must be answered: 
  • Is the particulate dense air inhaled into the respiratory tract during a haze event a vector for pathogens, including influenza A virus?
  •  Does heavy haze decrease the resistance of lung tissue to pathogenic microorganisms, thereby increasing the risk of respiratory disease?, 
  • Does influenza A virus (with its naturally higher incidence during winter and spring) merely happen to coincide with the seasonal haze? 
Conflicting lines of evidence exist for each of these questions, and additional research and data will be needed to reach dependable conclusions.