Reported Human Infections with Swine-Origin Influenza Viruses (SOIV) in the United States since 2005

As of October 31, 2011, 28 cases of human infection with swine origin influenza viruses have been reported in the United States. These are viruses that normally infect pigs. Like human influenza viruses, there are different subtypes and strains of swine-origin influenza viruses. The main swine influenza viruses circulating in U.S. pigs in recent years are swine triple reassortant (tr) H1N1 influenza virus, trH3N2 virus and trH1N2 virus. Of the 28 human cases reported since 2005, 12 have been trH1N1 viruses, 15 have been trH3N2 viruses and one has been a trH1N2 virus. All 28 persons infected with swine viruses recovered from their illness. Twenty cases occurred in children (persons 18 or younger) and 8 cases occurred in adults. In 24 cases, direct or indirect exposure to swine prior to onset of illness has been identified. Likely transmission of swine-origin influenza virus from close contact with an infected person has been observed in investigations of human infections with swine-origin influenza A virus, but has not resulted in sustained human-to-human transmission.