H7N9 Transmission Plummets After Live Poultry Market Closure

Troy Brown, RN

October 31, 2013

Closing live poultry markets (LPMs) during an avian influenza A H7N9 outbreak reduced poultry-to-human transmission of the disease by 97% to 99% in 4 Chinese cities where the virus was circulating between April and June 2013.

Hongjie Yu, MD, director of the Division for Infectious Diseases at the Chinese Center for Disease Control and Prevention, and colleagues developed a statistical model to quantify the effect of LPM closure on poultry-to-human transmission in Shanghai, Hangzhou, Huzhou, and Nanjing during an outbreak that began in early April 2013. Their results were published online October 31 in the Lancet.

The findings "support the idea that LPM exposure has a major role in human risk of avian influenza A H7N9 virus infection in urban areas," the authors write.

The researchers used information about age, sex, location, residence type (rural or urban area), and dates of illness onset from a database built by the Chinese Center for Disease Control and Prevention.

Of the 130 cases of avian influenza A H7N9 virus infection reported as of June 7, 2013, 85 occurred in Shanghai, Hangzhou, Huzhou, and Nanjing; 60 of these cases were included in the main analysis.

A total of 780 LPMs in those cities were closed, depopulated, and disinfected, and the pet bird trade was suspended, during the first 3 weeks of April.

After closure of the LPMs, the mean daily number of infections was reduced by 99% (95% credibility interval [CI], 93% - 100%) in Shanghai, 99% (95% CI, 92% - 100%) in Hangzhou, 97% (95% CI, 68% - 100%) in Huzhou, and 97% (95% CI, 81% - 100%) in Nanjing.

Because LPMs were the main source of confirmed avian influenza A H7N9 virus in these cities, the mean incubation period was estimated to be 3.3 days (95% CI, 1.4 - 5.7 days). "[T]he rapid drop in cases after LPM closure allowed us to estimate that the mean incubation period was about 3 days, instead of 1 week as preliminary epidemiological investigations had suggested," the authors write.

Closure of LPMs may be less effective in future outbreaks and informal ways of poultry trading, including smuggling may develop, note Guillaume Fournié, DrVetMed, PhD, a postdoctoral researcher in the Production and Population Health Department at the Royal Veterinary College, and Dirk U. Pfeiffer, DrMedVet, MACVSc, PhD, DipECVPH, a professor of veterinary epidemiology and head of the Veterinary Epidemiology, Economics and Public Health Group in the Department of Production and Population Health at Royal Veterinary College, Hatfield, United Kingdom, in an accompanying commentary.

"If LPM closure cannot be effectively enforced, unintended changes in the structure of networks could be triggered, possibly increasing the potential for disease spread, and probably resulting in reduced ability to do targeted surveillance and other risk management activities," Dr. Fournié and Dr. Pfeiffer write. "Therefore, before such an intervention is implemented, its feasibility and the likelihood of unintended adverse results should be carefully assessed."

"By contrast with LPM closure, a multisectoral approach leading to restructuring rather than destabilisation of the LPM system would be more likely to result in a sustainable reduction in the risk of disease spread while also protecting livelihoods and food security," the commentators conclude.

Funding for this study was provided by the Ministry of Science and Technology, China; Research Fund for the Control of Infectious Disease; Hong Kong University Grants Committee; China–US Collaborative Program on Emerging and Re-emerging Infectious Diseases; Harvard Center for Communicable Disease Dynamics; and the National Institutes of Health. One coauthor reports receipt of research funding from MedImmune and is a paid consultant for Crucell NV. One coauthor reports receipt of speaker honoraria from HSBC and CLSA. The other authors and commentators have disclosed no relevant financial relationships.

Lancet. Published online October 31, 2013. Article abstract, Comment extract

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