2009 Pandemic H1N1 Influenza
Novel influenza A virus strains appear at unpredictable intervals and can cause outbreaks on a global scale (pandemics) with sharply increased morbidity and mortality, especially in children and young adults (Simonsen et al., 1998; Monto, 2009). Pigs are susceptible to infection from influenza viruses of both avian and human origins, efficiently transmit infection, and play an important role in the generation of novel influenza viruses (Ma et al., 2009). In early 2009, a multiple reassortant (with genes from swine, human, and avian viruses) influenza A/H1N1 virus emerged in southern Mexico (Brownstein, Freifeld, & Madoff, 2009). Beginning in late February 2009, national surveillance systems in Mexico detected an unusual increase in influenza-like illness (ILI) cases, and in March and April there were increasing reports of previously healthy young adults hospitalized with severe pneumonia. This led to active surveillance in 23 hospitals in Mexico City and the identification of non-subtypable influenza A viruses (Perez-Padilla et al., 2009). In March 2009, two epidemiologically unrelated children in southern California were detected that had been infected with the new reassortant virus, but neither had had contact with pigs. This set off national alerts and the establishment of syndromic surveillance systems in schools, cities, and states across the country. In New York, the first indication of an outbreak came from a telephone report from a school nurse reporting an increase in febrile illness after students returned from spring break vacation to Mexico. This novel virus rapidly spread around the world causing the WHO to declare a pandemic on June 11, 2009 (Novel Swine-Origin Influenza A [H1N1] Virus Investigation Team et al., 2009; WHO, 2009). Fortunately, while the 2009 pandemic influenza A (H1N1) virus resulted in millions of illnesses, caused significant social disruption, and increased burden on health care systems, mortality rates from this virus were lower than that observed during previous pandemics.
Among the major policy domains associated with emerging and reemerging infectious disease outbreaks are surveillance and reporting, immunization, quarantine, travel and immigration restrictions, and restrictions related to the importation of food and animals.