2009 human H1N1 influenza (swine flu)

Abstract

The 2009 H1N1 influenza, initially known as swine flu, originated in North America in early 2009. This new strain of influenza A virus (H1N1) came to the attention of the international public health community when several foci of influenza-like illness were identified in Mexico, which had more than 850 cases of pneumonia, of whom 59 had died. Mild cases of influenza-like illness were also reported from Texas and California. Virus isolates were obtained from the cases in California and from samples of cases sent from Mexico to the Canadian National Public Health Laboratory in Winnipeg. Molecular analysis of these virus isolates showed that they were virtually identical and indicated that they represented a completely new, rapidly spreading strain of H1N1 virus, which appeared to have originated in swine. This was the first reassorted influenza virus to emerge since the 1968-1969 pandemic caused by the Hong Kong influenza virus. Under the new International Health Regulations (2005), this rapidly spreading, novel virus was quickly recognised by the World Health Organization as constituting a Public Health Emergency of International Concern, the first such emergency since the new International Health Regulations were introduced in mid-2007.