2009 Outbreak in Humans

The H1N1 viral strain implicated in the 2009 flu pandemic among humans often is called "swine flu" because initial testing showed many of the genes in the virus were similar to influenza viruses normally occurring in North American swine. Further research has shown that three-quarters or six out of the eight gene segments of the 2009 virus arose from the 1998 North American swine flu strains which emerged from the first-ever reported triple-hybrid virus of 1998.

In late April, Margaret Chan, the World Health Organization's director-general, declared a "public health emergency of international concern" under the rules of the WHO's new International Health Regulations when the first two cases of the H1N1 virus were reported in the United States, followed by hundreds of cases in Mexico. the initial cases in the USA and Mexico, on May 2, 2009, it was reported in pigs at a farm in Alberta, Canada, with a link to the outbreak in Mexico. The pigs are suspected to have caught this new strain of virus from a farm worker who recently returned from Mexico, then showed symptoms of an influenza-like illness. These are probable cases, pending confirmation by laboratory testing.

The new strain was initially described as an apparent reassortment of at least four strains of influenza A virus subtype H1N1, including one strain endemic in humans, one endemic in birds, and two endemic in swine. Subsequent analysis suggested it was a reassortment of just two strains, both found in swine. Although initial reports identified the new strain as swine influenza (i.e., a zoonosis originating in swine), its genetic origin was only later revealed to have been mostly a descendant of the triple-reassortment virus which emerged in factory farms in the United States in 1998. Several countries took precautionary measures to reduce the chances for a global pandemic of the disease. The 2009 swine flu has been compared to other similar types of influenza virus in terms of mortality: "in the US it appears that for every 1000 people who get infected, about 40 people need admission to hospital and about one person dies."There are fears that swine flu will become a major global pandemic at the end of the year (coinciding with the Northern Hemisphere winter months), with many countries planning major vaccination campaigns.

The 2009 flu pandemic, or swine flu, is a global outbreak of a new strain of influenza A virus subtype H1N1, a type of swine influenza, that was first detected in March and April 2009.The outbreak began in Veracruz, Mexico, with evidence that there had been an ongoing epidemic for months before it was officially recognized as such. The Mexican government closed most of Mexico City's public and private facilities in an attempt to contain the spread of the virus. However the virus continued to spread globally, clinics were overwhelmed by people infected, and the World Health Organization (WHO) and US Centers for Disease Control (CDC) stopped counting all cases and focused on tracking major outbreaks. On June 11, 2009, the WHO declared the outbreak a pandemic. As of November 20, 2009 (2009 -11-20)[update], the swine flu virus activity may have peaked in the U.S. and some European countries, while other countries report sharp increases.

While only mild symptoms are experienced by the majority of people,some have more severe symptoms. Mild symptoms may include include fever, sore throat, cough, headache, muscle or joint pains, and nausea, vomiting, or diarrhea. Those at risk of a more severe infection include: asthmatics, diabetics, those with obesity, heart disease, the immunocompromised, children with neurodevelopmental conditions, and pregnant women.

In addition, even for persons previously very healthy, a small percentage of patients will develop viral pneumonia. This manifests itself as increased breathing difficulty and typically occurs 3 to 6 days after initial onset of flu symptoms.

Similar to other influenza viruses, pandemic H1N1 is typically contracted by person to person transmission through respiratory droplets. Symptoms usually last 4 to 6 days. To avoid spreading the infection, it is recommended that those with symptoms stay home, away from school, work, and crowded places. Those with more severe symptoms or those in an at risk group may benefit from antivirals (oseltamivir or zanamivir). As of November 25, 2009 (2009 -11-25)[update], there are 8,452 confirmed deaths worldwide.