New Bird Flu Found to Be Less Deadly Than First Estimated

The H7N9 strain of bird flu that has killed 38 people in China since March is less deadly than had been supposed, according to the most detailed analysis of the outbreak so far.

The risk of death for patients admitted to a hospital with H7N9 infection is about 36 percent, researchers at the Chinese Center for Disease Control and Prevention and the University of Hong Kong wrote in The Lancet medical journal today. While initial reports of severe illness among most patients suggested the virus may be highly lethal, as many as about 27,000 undetected mild cases may have occurred, lowering the risk, the study said.

Still, H7N9 is only about half as deadly as the H5N1 bird flu strain that has killed about 60 percent of the 630 people it’s infected since 2003, the researchers wrote. The new virus, which has subsided with the onset of warmer weather and the closure of live bird markets in China, may rebound this year if it follows a similar pattern to H5N1, they said in a separate study.

“This potential lull should be an opportunity for discussion of preventive public health measures,” the authors wrote.

The virus has sickened 131 people in China and killed 39 since it emerged in March, the official Xinhua news agency reported June 9, citing China’s National Health and Family Planning Commission. Most cases were among people with exposure to live poultry, and there’s no evidence the virus can be transmitted between people, according to the Geneva-based World Health Organization.

The outbreak caused airline stocks and soybean prices to fall, prompting Chinese authorities to halt trading in live poultry, close bird markets and slaughter fowl to curb transmission. Shanghai, the city with the most cases, lifted a ban on live poultry sales last week as concern about the outbreak eased, according to the Shanghai Daily newspaper.

“It is reassuring that head-to-head comparison of the fatality risk of admitted patients infected with avian influenza A H7N9 or H5N1 suggests a substantially milder disease course for H7N9,” Cecile Viboud from the U.S. National Institutes of Health and Lone Simonsen of George Washington University wrote in an editorial accompanying the two papers.

H7N9 is more dangerous than the H1N1 swine flu virus that sparked the 2009 flu pandemic and killed about 21 percent of those infected in China, the authors wrote.

The WHO estimated the fatality risk of H7N9 at about 25 percent in a report last month.

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