Effect of closure of live poultry markets on poultry-to-person transmission of avian influenza A H7N9 virus: an ecological study
Dr Benjamin J Cowling PhD e 
, Dr Weizhong Yang MD d ,
, Dr Weizhong Yang MD d , Summary
Background
Transmission
of the novel avian influenza A H7N9 virus seems to be predominantly
between poultry and people. In the major Chinese cities of Shanghai,
Hangzhou, Huzhou, and Nanjing—where most human cases of infection have
occurred—live poultry markets (LPMs) were closed in April, 2013, soon
after the initial outbreak, as a precautionary public health measure.
Our objective was to quantify the effect of LPM closure in these cities
on poultry-to-person transmission of avian influenza A H7N9 virus.
Methods
We
obtained information about every laboratory-confirmed human case of
avian influenza A H7N9 virus infection reported in the four cities by
June 7, 2013, from a database built by the Chinese Center for Disease
Control and Prevention. We used data for age, sex, location, residence
type (rural or urban area), and dates of illness onset. We obtained
information about LPMs from official sources. We constructed a
statistical model to explain the patterns in incidence of cases reported
in each city on the basis of the assumption of a constant force of
infection before LPM closure, and a different constant force of
infection after closure. We fitted the model with Markov chain Monte
Carlo methods.
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.
Funding
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 US National
Institutes of Health. http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2813%2961904-2/abstract?rss=yes