China's CDC said yesterday in an extensive Q and A report posted in English that the source of the infections is probably poultry. It noted that H7 influenza infections in humans are uncommon, but have been confirmed in people who have direct contact with infected birds, especially during H7 outbreaks.
Between 1996 and 2009, human H7 infections were reported in the Netherlands, Italy, Canada, the United States, and England, with pathogens including H7N2, H7N3, and H7N7, the report said. Most of the infections involved conjunctivitis and mild upper respiratory symptoms.
The statement noted that H7N9 has previously been isolated only in birds, with outbreaks reported in the Netherlands, Japan, and the United States.
David Halvorson, DVM, an avian health expert at the University of Minnesota in St. Paul, told CIDRAP News that the subtype has infected poultry in the United States, but it's not likely to be from the same lineage as China's H7N9.
He said evidence of exposure to low-pathogenicity H7N9 was detected in US flocks in 2007, 2009, and 2011. "I believe chickens and turkeys in Nebraska, Minnesota, Illinois, Kentucky, and Tennessee were involved," Halvorson said.
Animal health officials in Shanghai today said tests on samples from some of the thousands of dead pigs that were recently retrieved from the Huangpu River were negative for avian influenza viruses, Xinhua, China's state news agency, reported today.
China's CDC said information about the clinical course of the disease is limited, but so far it appears that an acute fever, high temperature, cough, and respiratory infection symptoms occur early in the disease. More severe manifestations appear 5 to 7 days later, including severe pneumonia that can progress to acute respiratory distress syndrome and death.
So far no subclinical infections have been found in blood testing of contacts. "But we cannot rule out the possibility of human-to-human transmission until we know more about the virus characteristics and results from ongoing investigations," the Chinese statement said.