Swine Influenza in Humans

Swine flu viruses do not normally infect humans. However, sporadic human infections with swine flu have occurred. Most commonly, these cases occur in persons with exposure to infected pigs (e.g. children near pigs at a fair or workers in the swine industry). In addition, there have been documented cases of multiple persons becoming sick after exposure to one or a group of sick pigs and also cases of limited human-to-human spread of swine influenza viruses. Although the vast majority of human infections with swine influenza viruses do not result in human-to-human transmission, these cases should be fully investigated to be sure that such viruses are not spreading among humans and to limit further exposure of humans to infected animals if infected animals are identified.

Domestically, CDC reports these cases in its weekly influenza surveillance report, FluView. CDC also is legally required to report all cases of human infection with swine influenza viruses to the World Health Organization (WHO) as part of the International Health Regulations (IHR). The IHR began in 2007 with the goal of helping to prevent and respond to public health risks with potential global impact. The IHR requires countries to report certain disease outbreaks and public health events, including any confirmed case of human infection with a "novel" (non-human) influenza virus.

The links below offer information about human infections with swine origin influenza viruses.

For information about 2009 H1N1 influenza (initially referred to as “swine flu” when it was first detected), visit the archived CDC 2009 H1N1 Flu website.