What is swine flu? HIN1 Influenza is a respiratory disease of pigs caused by type A influenza viruses that causes regular outbreaks in pigs. People do not normally get swine flu, but human infections can and do happen. Swine flu viruses have been reported to spread from person-to-person, but in the past, this transmission was limited and not sustained beyond three people. Are there human infections with H1N1 flu in the U.S.? In late March and early April 2009, cases of human infection with H1N1 influenza A viruses were first reported in Southern California and near Guadalupe County, Texas. Other U.S. states have reported cases of H1N1 flu infection in humans and cases have been reported internationally as well. Updated case counts of confirmed H1N1 flu infections in the United States is available on the CDC website. CDC and local and state health agencies are working together to investigate this situatio.