A new type of flu began making people sick in China in 2013. Researchers quickly discovered that the virus was a type of avian influenza, known as H7N9, never before seen in humans. In one year the virus has surged twice, sickening 370 people in China and killing 115 (according to data available as of February 28).
As with seasonal flu, infections tapered off during the summer of 2013 but reappeared with colder weather. The second wave of H7N9 started earlier in the flu season and has sickened more people than the first wave did.
At least for now, H7N9 doesn’t spread easily from person to person. Only four families have multiple sick members that may have passed the virus through close contact. Scientists worry that if the virus infects many people, it may gain the ability to readily jump between humans, creating a pandemic.
Exposure to live poultry is the main infection route, with 82 percent of sick people in the first wave reporting recent contact with live animals, especially chickens.
Men and elderly at most risk
More men than women have become sick with H7N9 flu for reasons that are unknown. People over age 50, particularly older men, have also been more likely to die of the new bird flu. Children tend to have mild cases of the disease, and none are known to have died.
March 29, 2013: Six weeks into the outbreak, China’s Center for Disease Control and Prevention identifies H7N9.
April 11, 2013: The H7N9 virus includes genes recombined from three other viruses, scientists report.
May 23, 2013: H7N9 flu can be transmitted between ferrets through the air, researchers report.
July 3, 2013: H7N9 can infect human lung cells, researchers report, helping explain why it causes pneumonia.
Oct. 31, 2013: Closing live poultry markets is an effective way to limit H7N9 spread, a study concludes.
Dec. 1, 2013: As of this date, 34 percent of the 139 people who have been infected have died.
Jan. 27, 2014: After infected birds are found in a market, Hong Kong suspends the sale of live chickens and kills 20,000 birds to prevent the spread of the virus.
Feb. 13, 2014: Vietnam bans the importation of Chinese poultry.