BEIJING, June 24 (UPI) -- Almost a third of the confirmed cases of bird flu in China are fatal and although the cases have ended, health officials say the virus may return in the fall.
Studies by China's Center for Disease Control and Prevention found more than 130 cases since the H7N9 influenza strain appeared in February, medicaldaily.com. Thirty-seven patients died.
Researchers mined national surveillance data to conduct the analysis. In China, all hospitals were required to submit detailed medical reports on H7N9 cases to a central, government-run database.
Two studies, published in The Lancet, found a higher density of H7N9 in urban areas -- 72 percent in the cities versus the countryside.
Officials said the virus most likely jumped from chickens and ducks to humans. For both urban and rural locales, more than two-third of the cases were exposed to live poultry.
However, only 19 percent of the cases were linked to working with chickens via "occupational exposure" or raising backyard birds, but the most common context for exposure was visiting a chicken market at 33 percent.
"If H7N9 follows a similar pattern to H5N1, the epidemic could reappear in the autumn," the study authors wrote. "This potential lull should be an opportunity for discussion of definitive preventive public health measures."