China should close live poultry markets in big cities to disrupt the spread of a new strain of bird flu that resurfaced there earlier this month, scientists said, after a previous shutdown was found to have slashed the number of human cases.
In a study published in The Lancet medical journal on Thursday, researchers from Hong Kong and China said that while closing markets during the height of the first outbreak of H7N9 in April may have been costly, it reduced human infections dramatically and should be done again if cases rise as feared.
The findings - of a more than 97 percent reduction in the daily number of human cases of the new H7N9 strain after the markets were closed compared with before - should give policymakers confidence that the economic costs of shutting markets is balanced by significant health gains.
"(This) is a highly effective intervention to prevent human disease and protect public health," said Benjamin Cowling of Hong Kong University, who led the study and had it published in the Lancet medical journal.
Based on his findings, he said the best approach to minimize the spread of the H7N9 bird flu virus ahead of an expected surge in cases during the winter flu season would be to shut down markets wherever the virus is detected.
Two new human cases of H7N9 bird flu were found in China's eastern Zhejiang province in October, the first in what some flu experts fear may be a fresh epidemic of the deadly disease to come during China's colder winter months.
"This is of great concern because it reveals that the H7N9 virus has continued to circulate and now has the potential to re-emerge in a new outbreak of human disease this winter," said Cowling, echoing similar fears expressed by Chinese researchers in a study published last week.
Death rate 30 percent
Some 45 people have so far been killed by H7N9 flu strain, many of them during a flare-up in March and April just after the virus first emerged in humans earlier in February.
The World Health Organisation (WHO) says it has now recorded 137 laboratory confirmed cases, suggesting a death rate for the new strain of more than 30 percent.
At the start of April, several weeks after the first human cases of H7N9 bird flu emerged, 780 live poultry markets in the Chinese cities of Shanghai, Hangzhou, Huzhou and Nanjing were closed to try and halt virus spread.
The closures have been estimated to have cost more than 57 billion yuan ($9.35 billion), so Cowling's team set out to study whether those costs could be justified.
The team analyzed data on every laboratory confirmed case of H7N9 in those four cities up to June 1, 2013 and entered them into a statistical calculation method called a Bayesian model which was able to quantify the before-and-after effects of shutting down the markets.
The results found the closures cut the average daily number of H7N9 human infections by 99 percent in Shanghai, 99 percent in Hangzhou, 97 percent in Huzhou and 97 percent in Nanjing.
"Without this robust evidence, policymakers would struggle to justify further closures of LPMs because of the millennia-old culture of trading live birds and the potential huge economic loss on the poultry industry in China," said Cowling.
Yet with it, he added, the best course of action to minimize the spread of the virus ahead of the expected surge in infections in the winter would be sustained live poultry market closure in areas of high risk of disease spread, and immediate market closure in areas where the virus appears in future.