2009 swine flu pandemic

2009 swine flu pandemic
H1N1 map by confirmed cases.svg
  50,000+ confirmed cases
  5,000–49,999 confirmed cases
  500–4,999 confirmed cases
  50–499 confirmed cases
  5–49 confirmed cases
  1–4 confirmed cases
  No confirmed cases
Virus strainPandemic H1N1/09 virus
First outbreakNorth America[1][2]
Index caseVeracruz, Mexico[1][3]
Arrival dateSeptember 2008[4][5]
DateJanuary 2009 – 10 August 2010[6][7]
Confirmed cases491,382 (lab-confirmed)[8]
Suspected cases700 million to 1.4 billion (estimate)[9]
Lab confirmed deaths: 18,449 (reported to the WHO)[10]
Estimated excess death: 284,000[11]
Suspected cases have not been confirmed by laboratory tests as being due to this strain, although some other strains may have been ruled out.

The 2009 swine flu pandemic, caused by the H1N1 influenza virus and declared by the World Health Organization (WHO) from June 2009 to August 2010, is the third recent flu pandemic involving the H1N1 virus (the first being the 1918–1920 Spanish flu pandemic and the second being the 1977 Russian flu).[12][13] The first two cases were discovered independently in the United States in April 2009.[14] The virus appeared to be a new strain of H1N1 that resulted from a previous triple reassortment of bird, swine, and human flu viruses which further combined with a Eurasian pig flu virus,[15] leading to the term "swine flu".[16]

Some studies estimated that the real number of cases including asymptomatic and mild cases could be 700 million to 1.4 billion people—or 11 to 21 percent of the global population of 6.8 billion at the time.[9] The lower value of 700 million is more than the 500 million people estimated to have been infected by the Spanish flu pandemic.[17] However, the Spanish flu infected approximately a third of the world population at the time, a much higher proportion.[18]

The number of lab-confirmed deaths reported to the WHO is 18,449[10] and is widely considered a gross underestimate.[19] The WHO collaborated with the US Centers for Disease Control and Prevention (USCDC) and Netherlands Institute for Health Services Research (NIVEL) to produce two independent estimates of the influenza deaths that occurred during the global pandemic using two distinct methodologies. The 2009 H1N1 flu pandemic is estimated to have actually caused about 284,000 (range from 150,000 to 575,000) excess deaths by the WHO-USCDC study and 148,000–249,000 excess respiratory deaths by the WHO-NIVEL study.[20][21] A study done in September 2010 showed that the risk of serious illness resulting from the 2009 H1N1 flu was no higher than that of the yearly seasonal flu.[22] For comparison, the WHO estimates that 250,000 to 500,000 people die of seasonal flu annually.[23]

Unlike most strains of influenza, the pandemic H1N1/09 virus did not disproportionately infect adults older than 60 years; this was an unusual and characteristic feature of the H1N1 pandemic.[24] Even in the case of previously healthy people, a small percentage develop pneumonia or acute respiratory distress syndrome (ARDS). This manifests itself as increased breathing difficulty and typically occurs three to six days after initial onset of flu symptoms.[25][26] The pneumonia caused by flu can be either direct viral pneumonia or a secondary bacterial pneumonia. A November 2009 New England Journal of Medicine article recommended that flu patients whose chest X-ray indicates pneumonia receive both antivirals and antibiotics.[27] In particular, it is a warning sign if a child seems to be getting better and then relapses with high fever, as this relapse may be bacterial pneumonia.[28]

  1. ^ a b "Outbreak of Swine-Origin Influenza A (H1N1) Virus Infection: Mexico, March–April 2009". The Centers for Disease Control and Prevention (CDC). 30 April 2009. Archived from the original on 20 March 2020. Retrieved 20 March 2020.
  2. ^ "Origin of 2009 H1N1 Flu (Swine Flu): Questions and Answers". Centers for Disease Control and Prevention (CDC). 25 November 2009. Archived from the original on 18 March 2020. Retrieved 20 March 2020.
  3. ^ Perez-Padilla R, de la Rosa-Zamboni D, Ponce de Leon S, Hernandez M, Quiñones-Falconi F, Bautista E, et al. (August 2009). "Pneumonia and respiratory failure from swine-origin influenza A (H1N1) in Mexico". The New England Journal of Medicine. 361 (7): 680–89. doi:10.1056/NEJMoa0904252. PMID 19564631.
  4. ^ Cite error: The named reference Nature was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference circles globe was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference Reuters6-11 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference WHO declares H1N1 Pandemic over was invoked but never defined (see the help page).
  8. ^ "Weekly Virological Update on 05 August 2010". World Health Organization (WHO). 5 August 2010. Archived from the original on 7 August 2015. Retrieved 8 April 2020.
  9. ^ a b Roos R (8 August 2011). "Study puts global 2009 H1N1 infection rate at 11% to 21%". Center for Infectious Disease Research and Policy.
  10. ^ a b "Pandemic (H1N1) 2009". World Health Organization (WHO). 6 August 2010. Archived from the original on 27 March 2011. Retrieved 8 April 2020.
  11. ^ "CDC H1N1 Flu | Influenza Diagnostic Testing During the 2009–2010 Flu Season". www.cdc.gov. Retrieved 4 April 2020.
  12. ^ "Influenza Pandemic Plan. The Role of WHO and Guidelines for National and Regional Planning" (PDF). World Health Organization. April 1999. pp. 38, 41. Archived (PDF) from the original on 3 December 2020.
  13. ^ Michaelis M, Doerr HW, Cinatl J (August 2009). "Novel swine-origin influenza A virus in humans: another pandemic knocking at the door". Medical Microbiology and Immunology. 198 (3): 175–83. doi:10.1007/s00430-009-0118-5. PMID 19543913. S2CID 20496301.
  14. ^ Centers for Disease Control Prevention (CDC) (24 April 2009). "Swine Influenza A (H1N1) Infection in Two Children – Southern California, March–April 2009". Morbidity and Mortality Weekly Report. CDC. 58 (15): 400–402. PMID 19390508.
  15. ^ Trifonov V, Khiabanian H, Rabadan R (July 2009). "Geographic dependence, surveillance, and origins of the 2009 influenza A (H1N1) virus". The New England Journal of Medicine. 361 (2): 115–19. doi:10.1056/NEJMp0904572. PMID 19474418. S2CID 205105276.
  16. ^ Hellerman C (11 June 2009). "Swine flu 'not stoppable,' World Health Organization says". CNN. Archived from the original on 7 March 2010. Retrieved 3 April 2010.
  17. ^ Kelly H, Peck HA, Laurie KL, Wu P, Nishiura H, Cowling BJ (5 August 2011). "The age-specific cumulative incidence of infection with pandemic influenza H1N1 2009 was similar in various countries prior to vaccination". PLOS ONE. 6 (8): e21828. Bibcode:2011PLoSO...621828K. doi:10.1371/journal.pone.0021828. PMC 3151238. PMID 21850217.
  18. ^ Hagemann H (2 April 2020). "The 1918 Flu Pandemic Was Brutal, Killing More Than 50 Million People Worldwide". NPR. Retrieved 24 July 2020.
  19. ^ WHO. "Summary of WHO Technical Consultation: H1N1pdm Mortality Estimates, 25-26 October 2011" (PDF). Retrieved 1 November 2021.
  20. ^ "First Global Estimates of 2009 H1N1 Pandemic Mortality Released by CDC-Led Collaboration". cdc.gov. 25 June 2012. Retrieved 31 January 2020.
  21. ^ Simonsen L, Spreeuwenberg P, Lustig R, Taylor RJ, Fleming DM, Kroneman M, et al. (November 2013). "Global mortality estimates for the 2009 Influenza Pandemic from the GLaMOR project: a modeling study". PLOS Medicine. 10 (11): e1001558. doi:10.1371/journal.pmed.1001558. PMC 3841239. PMID 24302890.
  22. ^ DeNoon DJ. "H1N1 Swine Flu No Worse Than Seasonal Flu". WebMD. Retrieved 13 March 2020.
  23. ^ Roos R (27 June 2012). "CDC estimate of global H1N1 pandemic deaths: 284,000". CIDRAP. Retrieved 23 March 2020.
  24. ^ Bautista E, Chotpitayasunondh T, Gao Z, Harper SA, Shaw M, Uyeki TM, et al. (May 2010). "Clinical aspects of pandemic 2009 influenza A (H1N1) virus infection". The New England Journal of Medicine. 362 (18): 1708–19. doi:10.1056/NEJMra1000449. hdl:2381/15212. PMID 20445182.
  25. ^ "Clinical features of severe cases of pandemic influenza". Geneva, CH: World Health Organization (WHO). 16 October 2009. Archived from the original on 25 October 2009. Retrieved 25 October 2009.
  26. ^ Lin II RG (21 November 2009). "When to take a sick child to the ER". Los Angeles Times. Archived from the original on 25 November 2009. Retrieved 4 January 2010.
  27. ^ Jain S, Kamimoto L, Bramley AM, Schmitz AM, Benoit SR, Louie J, et al. (November 2009). "Hospitalized patients with 2009 H1N1 influenza in the United States, April–June 2009". The New England Journal of Medicine. 361 (20): 1935–44. CiteSeerX doi:10.1056/NEJMoa0906695. PMID 19815859. This study involved a total of 272 patients, which represents approximately 25% of US hospitalized patients with lab-confirmed H1N1 whose cases were reported to the US Centers for Disease Control and Prevention (CDC) from 1 May 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" [Outcomes section, 2nd paragraph] and also that "only 73% of patients with radiographic evidence of pneumonia received antiviral drugs, whereas 97% received antibiotics." [Discussion section, 8th paragraph]. It is recommended that such patients receive both.
  28. ^ Cite error: The named reference DeniseGradySept3 was invoked but never defined (see the help page).

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