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.
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.
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).
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.About this time in the fall of 1983, my family and I discovered Qingping Market in downtown Guangzhou. It was a big live market, and it didn't deal only in chickens. You could buy live owls, kittens, raccoons,and snakes, as well as freshly killed dogs, their fur seared off and hanging from hooks through their jaws. (Dogs with black fur were considered especially warming in cold weather.)
We were appalled, of course, as a Canadian family used to buying its meat shrink-wrapped in a supermarket or butcher shop, and whisking it home to a fridge or freezer. After our first visit we said we'd never go back. But we went back. Qingping Market had a lot to teach us.
China in 1983 was only a few years out of the Cultural Revolution, and only three or four years into Deng Xiaoping's far greater revolution, which made the country what it is today. But in 1983, a wristwatch was a hot black-market item and we foreigners had better be able to account for every one we brought into (and took out of) the country. It was nothing special to see a dismembered pig being taken to market on the back of a bike amid the thousands of other bikes.
For much of the year, China is a fiercely hot country. Not until November did Guangzhou, at roughly the latitude of Havana, cool down to California-spring levels. Christmas was a chilly affair in an apartment designed to lose heat. But we did have a Romanian refrigerator, which was more than most Chinese could say.
Given the fact of life that organic matter rots fast in hot, humid weather (a teaching colleague lost his beautiful silk suit and some shoes the next spring), it was simple realism to eat meat that had been alive just moments before you put it in your wok.
So the shoppers in Qingping picked their snakes and fish live and saw them killed on the spot. And the same was true of the chickens and ducks. My daughters once watched one of our neighbours, a retired professor, come out in the courtyard to feed his personal flock of chickens; then he picked one up, wrung its neck, and took it inside for lunch.
Better than most foreigners (and most young Chinese), I understand how far China has come in thirty short years. It is humanity's unrecognized great achievement of the past millennium.
But I suspect that old habits die hard. Not everyone in modern China has a refrigerator, Romanian or otherwise. Chinese power failures are still frequent, so commercial freezers aren't trustworthy. And the Chinese understand food as most of us westerners do not—as a matter of literal life or death.
Northern Chinese like to poke fun at the southerners as people who will eat anything with four legs except a table. But hunger is a recurrent horror in all of China, and many alive today remember the ghastly famines of the Great Leap Forward in the 1950s and early 60s.
So it's understandable that people today still want their food as fresh as possible, especially the poultry that provides so much protein to hundreds of millions. Hence the live markets, which—if they're like Qingping in 1983—feature rivulets of blood running through the cobblestones. Even you might get used to watching your dinner killed if your alternative was E. coli or salmonella or cholera or worse.
The closure of live "wet" markets is therefore a major step, and a politically dangerous one for the Chinese authorities. They have to gamble that consumers will understand how serious H7N9 is as a food-safety issue, making frozen or chilled meat a necessary option. Some day we in the sanitized West may face the same choice. If so, I hope we're as sensible and realistic as the Chinese have always been.