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The 2009 flu pandemic or swine flu was an influenza pandemic, and the second of the two pandemics involving H1N1 influenza virus (the first of them being the 1918 flu pandemic), albeit in a new version. First described in April 2009, the virus appeared to be a new strain of H1N1 which resulted when a previous triple reassortment of bird, swine and human flu viruses further combined with a Eurasian pig flu virus, leading to the term "swine flu". Unlike most strains of influenza, H1N1 does not disproportionately infect adults older than 60 years; this was an unusual and characteristic feature of the H1N1 pandemic. Even in the case of previously very healthy people, a small percentage will develop pneumonia or acute respiratory distress syndrome (ARDS). This manifests itself as increased breathing difficulty and typically occurs 3–6 days after initial onset of flu symptoms.〔 〕 The pneumonia caused by flu can be either direct viral pneumonia or a secondary bacterial pneumonia. In fact, a November 2009 ''New England Journal of Medicine'' article recommends that flu patients whose chest X-ray indicates pneumonia receive both antivirals and antibiotics.〔 This study involved a total of 272 patients, which represents approximately 25% of U.S. hospitalized patients with lab-confirmed H1N1 whose cases were reported to the U.S. Centers for Disease Control and Prevention (CDC) from 1 May 2009, to 9 June 2009. The study found that "the only variable that was significantly associated with a positive outcome was the receipt of antiviral drugs within two days after the onset of illness" (section, 2nd paragraph ) and also that "only 73% of patients with radiographic evidence of pneumonia received antiviral drugs, whereas 97% received antibiotics." (section, 8th paragraph ). It is recommended that such patients receive both.〕 In particular, it is a warning sign if a child (and presumably an adult) seems to be getting better and then relapses with high fever, as this relapse may be bacterial pneumonia.〔 Initially coined an "outbreak", the stint began in the state of 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, it continued to spread globally, and clinics in some areas were overwhelmed by infected people. In late April the World Health Organization (WHO) declared its first ever "public health emergency of international concern," or PHEIC,〔http://www.who.int/mediacentre/news/statements/2009/h1n1_20090425/en/〕 and in June the WHO and the U.S. CDC stopped counting cases and declared the outbreak a pandemic. Despite being informally called "swine flu", the H1N1 flu virus cannot be spread by eating pork or pork products;〔 similar to other influenza viruses, it is typically contracted by person to person transmission through respiratory droplets. Symptoms usually last 4–6 days. Antivirals (oseltamivir or zanamivir) were recommended for those with more severe symptoms or those in an at-risk group.〔 The pandemic began to taper off in November 2009, and by May 2010, the number of cases was in steep decline. On 10 August 2010, the Director-General of the WHO, Margaret Chan, announced the end of the H1N1 pandemic, and announced that the H1N1 influenza event has moved into the post-pandemic period. According to the latest WHO statistics (as of July 2010), the virus has killed more than 18,000 people since it appeared in April 2009, however they state that the total mortality (including deaths unconfirmed or unreported) from the H1N1 strain is "unquestionably higher".〔 Critics claimed the WHO had exaggerated the danger, spreading "fear and confusion" rather than "immediate information". The WHO began an investigation to determine whether it had "frightened people unnecessarily". A flu follow-up study done in September 2010, found that "the risk of most serious complications was not elevated in adults or children." In an 5 August 2011 ''PLoS ONE'' article, researchers estimated that the 2009 H1N1 global infection rate was 11% to 21%, lower than what was previously expected. However, by 2012, research showed that as many as 579,000 people could have been killed by the disease, as only those fatalities confirmed by laboratory testing were included in the original number, and meant that many of those without access to health facilities went uncounted. The majority of these deaths occurred in Africa and Southeast Asia. Experts, including the WHO, have agreed that an estimated 284,500 people were killed by the disease, much higher than the initial death toll. ==Classification== The initial outbreak was called the "H1N1 influenza", or "Swine Flu" by American media. It is called the pandemic H1N1/09 virus by the WHO, while the U.S. Centers for Disease Control and Prevention refer to it as "novel influenza A (H1N1)" or "2009 H1N1 flu". In the Netherlands, it was originally called "Pig Flu", but is now called "New Influenza A (H1N1)" by the national health institute, although the media and general population use the name "Mexican Flu". South Korea and Israel briefly considered calling it the "Mexican virus". Later, the South Korean press used "SI", short for "swine influenza". Taiwan suggested the names "H1N1 flu" or "new flu", which most local media adopted. The World Organization for Animal Health proposed the name "North American influenza". The European Commission adopted the term "novel flu virus". 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「2009 flu pandemic」の詳細全文を読む スポンサード リンク
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