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Influenza, commonly known as the flu, is an infectious disease caused by an influenza virus.[1] Symptoms can be mild to severe.[4] The most common symptoms include: high fever, runny nose, sore throat, muscle pains, headache, coughing, sneezing, and feeling tired.[1] These symptoms typically begin two days after exposure to the virus and most last less than a week.[1] The cough, however, may last for more than two weeks.[1] In children, there may be diarrhea and vomiting, but these are not common in adults.[5] Diarrhea and vomiting occur more commonly in gastroenteritis, which is an unrelated disease and sometimes inaccurately referred to as "stomach flu" or the "24-hour flu".[5] Complications of influenza may include viral pneumonia, secondary bacterial pneumonia, sinus infections, and worsening of previous health problems such as asthma or heart failure.[2][4]

Three of the four types of influenza viruses affect humans: Type A, Type B, and Type C.[2][6] Type D has not been known to infect humans, but is believed to have the potential to do so.[6][7] Usually, the virus is spread through the air from coughs or sneezes.[1] This is believed to occur mostly over relatively short distances.[8] It can also be spread by touching surfaces contaminated by the virus and then touching the mouth or eyes.[4][8] A person may be infectious to others both before and during the time they are showing symptoms.[4] The infection may be confirmed by testing the throat, sputum, or nose for the virus.[2] A number of rapid tests are available; however, people may still have the infection even if the results are negative.[2] A type of polymerase chain reaction that detects the virus's RNA is more accurate.[2]

Frequent hand washing reduces the risk of viral spread.[3] Wearing a surgical mask is also useful.[3] Yearly vaccinations against influenza are recommended by the World Health Organization for those at high risk.[1] The vaccine is usually effective against three or four types of influenza.[1] It is usually well-tolerated.[1] A vaccine made for one year may not be useful in the following year, since the virus evolves rapidly.[1] Antiviral drugs such as the neuraminidase inhibitor oseltamivir, among others, have been used to treat influenza.[1] The benefit of antiviral drugs in those who are otherwise healthy do not appear to be greater than their risks.[9] No benefit has been found in those with other health problems.[9][10]

Influenza spreads around the world in yearly outbreaks, resulting in about three to five million cases of severe illness and about 250,000 to 500,000 deaths.[1] About 20% of unvaccinated children and 10% of unvaccinated adults are infected each year.[11] In the northern and southern parts of the world, outbreaks occur mainly in the winter, while around the equator, outbreaks may occur at any time of the year.[1] Death occurs mostly in the young, the old, and those with other health problems.[1] Larger outbreaks known as pandemics are less frequent.[2] In the 20th century, three influenza pandemics occurred: Spanish influenza in 1918 (~50 million deaths), Asian influenza in 1957 (two million deaths), and Hong Kong influenza in 1968 (one million deaths).[12] The World Health Organization declared an outbreak of a new type of influenza A/H1N1 to be a pandemic in June 2009.[13] Influenza may also affect other animals, including pigs, horses, and birds.[14]

ReferencesEdit

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 Influenza (Seasonal) Fact sheet N°211”. March 2014. http://www.who.int/mediacentre/factsheets/fs211/en/. 
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Longo, Dan L. (2012). „Chapter 187: Influenza”. Harrison's principles of internal medicine. (ed. 18th). New York: McGraw-Hill. ISBN 978-0-07-174889-6. 
  3. 3.0 3.1 3.2 Jefferson T, Del Mar CB, Dooley L, et al. (2011). "Physical interventions to interrupt or reduce the spread of respiratory viruses" (PDF). Cochrane Database Syst Rev (7): CD006207. doi:10.1002/14651858.CD006207.pub4. PMID 21735402. 
  4. 4.0 4.1 4.2 4.3 Key Facts about Influenza (Flu) & Flu Vaccine”. 9 September 2014. Archived from the original on 2 December 2014. https://web.archive.org/web/20141202191706/http://www.cdc.gov/flu/keyfacts.htm. Accesat la 26 November 2014. 
  5. 5.0 5.1 Duben-Engelkirk, Paul G.; Engelkirk, Janet (2011). Burton's microbiology for the health sciences (ed. 9th). Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. p. 314. ISBN 978-1-60547-673-5. https://books.google.com/books?id=RaVKCQI75voC&pg=PA355. 
  6. 6.0 6.1 Types of Influenza Viruses Seasonal Influenza (Flu)” (în en-us). 27 September 2017. https://www.cdc.gov/flu/about/viruses/types.htm. Accesat la 28 September 2018. 
  7. Shuo Su; Xinliang Fu; Gairu Li; Fiona Kerlin; Michael Veit (25 August 2017). "Novel Influenza D virus: Epidemiology, pathology, evolution and biological characteristics". Virulence. 8 (8): 1580–91. doi:10.1080/21505594.2017.1365216. PMC 5810478Freely accessible. PMID 28812422. 
  8. 8.0 8.1 Brankston G, Gitterman L, Hirji Z, Lemieux C, Gardam M (April 2007). "Transmission of influenza A in human beings". Lancet Infect Dis. 7 (4): 257–65. doi:10.1016/S1473-3099(07)70029-4. PMID 17376383. 
  9. 9.0 9.1 Michiels B, Van Puyenbroeck K, Verhoeven V, Vermeire E, Coenen S (2013). "The value of neuraminidase inhibitors for the prevention and treatment of seasonal influenza: a systematic review of systematic reviews". PLOS One. 8 (4): e60348. Bibcode:2013PLoSO...860348M. doi:10.1371/journal.pone.0060348. PMC 3614893Freely accessible. PMID 23565231. 
  10. Ebell MH, Call M, Shinholser J (April 2013). "Effectiveness of oseltamivir in adults: a meta-analysis of published and unpublished clinical trials". Family Practice. 30 (2): 125–33. doi:10.1093/fampra/cms059. PMID 22997224. 
  11. Somes MP, Turner RM, Dwyer LJ, Newall AT (May 2018). "Estimating the annual attack rate of seasonal influenza among unvaccinated individuals: A systematic review and meta-analysis". Vaccine. 36 (23): 3199–3207. doi:10.1016/j.vaccine.2018.04.063. PMID 29716771. 
  12. Ten things you need to know about pandemic influenza”. World Health Organization. 14 October 2005. http://www.who.int/csr/disease/influenza/pandemic10things/en/index.html. 
  13. Chan, Margaret (11 June 2009). „World now at the start of 2009 influenza pandemic”. World Health Organization. http://www.who.int/mediacentre/news/statements/2009/h1n1_pandemic_phase6_20090611/en/index.html. 
  14. Oxford textbook of zoonoses : biology, clinical practice, and public health control (ed. 2.). Oxford u.a.: Oxford Univ. Press. 2011. p. 332. ISBN 978-0-19-857002-8. https://books.google.com/books?id=S90mOwgdz9kC&pg=PA332. 
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