The Outbreak of the Novel H1N1 Flu Virus in 2009
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The virus genes were a combination of genes most closely related to North American swine-lineage H1N1 and Eurasian lineage swine-origin H1N1 influenza viruses. Because of this, initial reports referred to the virus as a swine origin influenza virus. However, investigations of initial human cases did not identify exposures to pigs and quickly it became apparent that this new virus was circulating among humans and not among U.S. pig herds. Infection with this new influenza A virus (then referred to as ‘swine origin influenza A virus’) was first detected in a 10-year-old patient in California on April 15, 2009, who was tested for influenza as part of a clinical study. Laboratory testing at CDC confirmed that this virus was new to humans. Two days later, CDC laboratory testing confirmed a second infection with this virus in another patient, an 8-year-old living in California about 130 miles away from the first patient who was tested as part of an influenza surveillance project. There was no known connection between the two patients. Laboratory analysis at CDC determined that the viruses obtained from these two patients were very similar to each other, and different from any other influenza viruses previously seen either in humans or animals. Testing showed that these two viruses were resistant to the two antiviral drugs amantadine and rimantadine, but susceptible to the antiviral drugs oseltamivir and zanamivir. CDC began an immediate investigation into the situation in coordination with state and local animal and human health officials in California.The cases of 2009 H1N1 flu in California occurred in the context of sporadic reports of human infection with North American-lineage swine influenza viruses in the United States, most often associated with close contact with infected pigs. (During December 2005 – January 2009, 12 cases of human infection with swine influenza were reported; five of these 12 cases occurred in patients who had direct exposure to pigs, six patients reported being near pigs, and the source of infection in one case was unknown). Human-to-human spread swine influenza viruses had been rarely documented and had not been known to result in widespread community outbreaks among people. In mid-April of 2009, however, the detection of two patients infected with swine origin flu viruses 130 miles apart, raised concern that a novel swine-origin influenza virus had made its way into the human population and was spreading among people.
During the past century, there were three major influenza pandemics: in 1918 (H1N1), 1957 (H2N2), and 1968 (H3N2). The most serious influenza pandemic in recent history is the 1918 Spanish flu that killed over 50 million people worldwide. The latter two pandemics were milder than the 1918 one but still resulted in significant mortality, with close to 2 million people dying from the 1957 virus and 1 million from the 1968 virus (Perez-Padilla R, de-la-Rosa-Zamboni D, 2009). Because of the real threat of a new influenza pandemic, international public health agencies called for the development of preparedness plans that would ensure the strengthening of national and global response capacity. As a result, countries began developing pandemic influenza plans in the late 1990's, and many countries had plans in place by 2005. In the United States, the National Strategic Plan for Pandemic Influenza was published in November of 2005 (Gómez-G|$$|Aaomez A, 2009).
We performed a literature search of PubMed using the following keywords: H1N1, influenza, vaccine, pregnancy, children, treatment, epidemiology, and review. Studies were selected for inclusion in this review on the basis of their relevance.
Belshe R. The origins of pandemic influenza-lessons from the 1918 virus. N Engl J Med. 2005
CDC. Swine influenza A (H1N1) infection in two children -Southern California, March-April 2009. MMWR—Morb Mortal Wk Rep. 2009
Perez-Padilla R, de-la-Rosa-Zamboni D, Ponce-de-Leon S, et al. Pneumonia and respiratory failure from swine-origin influenza A (H1N1) in Mexico. N Engl J Med. 2009
CDC. Update: Novel influenza A (H1N1) virus infection—Mexico, March-May 2009. MMWR- Morb Mortal Wk Rep. 2009
Gómez-G|$$|Aaomez A, Magaña-Aquino M, García-Sepúlveda C, et al. Severe pneumonia associated with pandemic (H1N1) 2009