Thursday, October 31, 2013

The Lancet: Poultry Market Closure Effect On H7N9 Transmission

Photo: ©FAO/Tariq Tinazay

Credit FAO 

 



# 7922

 


We’ve a report in The Lancet this morning that quantifies the benefits of closing live poultry markets in order to curb the spread of the H7N9 virus.  This infection control practice  – while costly, and not particularly popular among many in China – was credited with dramatically reduced the number of human infections with the virus in a very short period of time last spring.

 

Since that time, caveats about visiting live poultry markets have been included in nearly every public health statement issued by Hong Kong (and others) to travelers headed to mainland China. Last month Zeng Guang, chief epidemiologist at the China’s CDC, urged:

 

. . . .  the public to take precautions such as to avoid staying in public places for long and to be aware of good personal hygiene, including frequent hand-washing. In addition, to prevent H7N9 infection, "people shouldn't go to live poultry markets", he said. - Chinese CDC: Be Alert For H7N9

 

While poultry markets were closed in April and May in H7N9 affected regions, most have since re-opened, sparking fears that another round of human H7N9 cases may emerge this winter.

 

 

Effect of closure of live poultry markets on poultry-to-person transmission of avian influenza A H7N9 virus: an ecological study

Hongjie Yu MD a †, Joseph T Wu PhD e †, Dr Benjamin J Cowling PhD e , Qiaohong Liao MD a, Vicky J Fang MPhil e, Sheng Zhou MD a, Peng Wu PhD e, Hang Zhou MD a, Eric H Y Lau PhD e, Danhuai Guo PhD f, Michael Y Ni MPH e, Zhibin Peng MD a, Luzhao Feng MD a, Hui Jiang MD a, Huiming Luo MD b, Qun Li MD c, Zijian Feng MD c, Yu Wang PhD d, Dr Weizhong Yang MD d , Prof Gabriel M Leung MD e

Findings

85 human cases of avian influenza A H7N9 virus infection were reported in Shanghai, Hangzhou, Huzhou, and Nanjing by June 7, 2013, of which 60 were included in our main analysis. Closure of LPMs reduced the mean daily number of infections by 99% (95% credibility interval 93—100%) in Shanghai, by 99% (92—100%) in Hangzhou, by 97% (68—100%) in Huzhou, and by 97% (81—100%) in Nanjing. Because LPMs were the predominant source of exposure to avian influenza A H7N9 virus for confirmed cases in these cities, we estimated that the mean incubation period was 3·3 days (1·4—5·7).

Interpretation

LPM closures were effective in the control of human risk of avian influenza A H7N9 virus infection in the spring of 2013. In the short term, LPM closure should be rapidly implemented in areas where the virus is identified in live poultry or people. In the long term, evidence-based discussions and deliberations about the role of market rest days and central slaughtering of all live poultry should be renewed.

 

 

We’ve seen in China, Indonesia, and in other countries attempts to close or strictly regulate live bird markets in the past – only to be met with tremendous public resistance (see 2009 blog China Announces Plan To Shut Down Live Poultry Markets In Many Cities).  Their ambitious plan, announced 4 years ago to `shut live poultry markets in all large and medium-sized cities throughout China’, obviously never happened.

 

Purchasing live market birds is deeply ingrained in the culture, as it reassures the buyer that the bird is both fresh and healthy.   

 

When dealing with a highly pathogenic (in poultry) virus like H5N1 - where birds often sicken and die - vendors and the public can usually see the effect of the virus.  Not so with H7N9, as birds can carry it and remain healthy, while in humans it can produce severe illness.

 

Convincing vendors, and the public, that their perfectly healthy looking duck or chicken is a threat to human health can be a tough sell. 

 

Add to that the economic impact of closing live markets – the often conflicting goals and mandate of  China’s Ministry of Agriculture - and prospects for a quick and permanent solution to the sale of live market birds appears low.

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