Swine influenza epidemiology and demographics: Difference between revisions

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{{Swine influenza}}
{{Swine influenza}}
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==Overview==
Swine influenza usually occurs in outbreaks/pandemics, and the incidence may vary greatly from one year to another. The 2009 H1N1 global infection rate was 11% to 21%. During the 2009 swine influenza outbreak, the incidence in the USA was approximately 18,000 per 100,000 individuals (a total of 60 million cases) with approximately 265,000 hospitalizations reported. The worldwide case fatality rate is unknown, but is thought to range from 15,000 (initial reports) to 500,000 when patients with no healthcare access were counted. Individuals of all age groups may be affected by swine influenza. There is no gender or racial predilection to the development of swine influenza.


== Epidemiology ==
== Epidemiology and Demographics ==
===Incidence===
*Swine influenza usually occurs in outbreaks/pandemics, and the incidence may vary greatly from one year to another.
*The 2009 H1N1 global infection rate was 11% to 21%.<ref>{{cite news|last=Roos|first=Robert|title=Study puts global 2009 H1N1 infection rate at 11% to 21%|url=http://www.cidrap.umn.edu/cidrap/content/influenza/swineflu/news/aug0811serologic.html|newspaper=CIDRAP|date=8 August 2011| accessdate= 10 August 2011 <!--DASHBot-->}}</ref>
*During the 2009 swine influenza outbreak, the incidence in the USA was approximately 18,000 per 100,000 individuals (a total of 60 million cases) with approximately 265,000 hospitalizations reported.<ref>{{Cite news|url=http://www.cdc.gov/media/transcripts/2010/t100329.htm|title=Press Briefing Transcripts
CDC 2009 H1N1 Flu Media Briefing|publisher=CDC|accessdate=21 Feb 2016}}</ref>


===Outbreaks in swine===
===Case-Fatality Rate===
*The exact case fatality rate is unknown.
*During the 2009 swine influenza outbreak, initial reports stated that a total of 15,000-18,000 individuals died worldwide, the majority of whom were under 65 years of age.<ref name="WHOMay14update"/><ref>{{Cite news|url=http://www.redorbit.com/news/health/1893907/h1n1_still_a_pandemic_says_who/|title=H1N1 Still A Pandemic, Says WHO|publisher=redOrbit|accessdate=10 August 2010}}</ref> Three years later, however, it was speculated that more than 280,000 - 500,000 individuals may have died due to 2009 swine influenza. The initial underestimation was thought to be caused by not counting individuals with no access to healthcare in developing countries.<ref>{{cite journal |author=Dawood FS, Iuliano AD, Reed C |title=Estimated global mortality associated with the first 12 months of 2009 pandemic influenza A H1N1 virus circulation: a modelling study |journal=Lancet Infect Dis |volume=12 |issue=9 |pages=687–95 |date=September 2012 |pmid=22738893 |doi=10.1016/S1473-3099(12)70121-4 |display-authors=etal}}</ref><ref>{{cite web|url=http://www.cdc.gov/flu/spotlights/pandemic-global-estimates.htm|title=First Global Estimates of 2009 H1N1 Pandemic Mortality Released by CDC-Led Collaboration|date=25 June 2012|publisher=Centers for Disease Control and Prevention (CDC)|accessdate=3 July 2012}}</ref><ref>{{cite news|title=Swine flu killed 250,000 - 15 TIMES the number of people reported, claims international study|author=Goodenough, T.|url=http://www.dailymail.co.uk/news/article-2164899/Swine-flu-killed-15-TIMES-number-people-reported-claims-international-study.html#ixzz1zXHh5Ky4|newspaper=Mail Online|date=26 June 2012|accessdate=3 July 2012}}</ref>


==== 2007 Philippine outbreak ====
===Age===
*Individuals of all age groups may be affected by swine influenza.<ref name="Swine flu affect the young">{{cite web|url=http://bulletin.aarp.org/yourhealth/diseases/articles/swine_flus_tendency_to_strike_the_young_is_causing_confusion.html |title=Swine flu's tendency to strike the young is causing confusion |date=18 September 2009|work=Los Angeles Times |first=Karen |last=Kaplan |accessdate=18 September 2009| archiveurl= http://web.archive.org/web/20090919215923/http://bulletin.aarp.org/yourhealth/diseases/articles/swine_flus_tendency_to_strike_the_young_is_causing_confusion.html| archivedate= 19 September 2009 <!--DASHBot-->| deadurl= no}}</ref>
*Compared to the elderly, younger individuals are at higher risk of developing swine influenza. It is thought that older individuals may have a higher degree of cross-protection against influenza infection.<ref name="Swine flu affect the young">{{cite web|url=http://bulletin.aarp.org/yourhealth/diseases/articles/swine_flus_tendency_to_strike_the_young_is_causing_confusion.html |title=Swine flu's tendency to strike the young is causing confusion |date=18 September 2009|work=Los Angeles Times |first=Karen |last=Kaplan |accessdate=18 September 2009| archiveurl= http://web.archive.org/web/20090919215923/http://bulletin.aarp.org/yourhealth/diseases/articles/swine_flus_tendency_to_strike_the_young_is_causing_confusion.html| archivedate= 19 September 2009 <!--DASHBot-->| deadurl= no}}</ref>
*Small children and the elderly are at higher risk of developing swine flu-related complications.


On August 20, 2007 Department of Agriculture officers investigated the outbreak of swine flu in Nueva Ecija and Central Luzon, Philippines. The mortality rate is less than 10% for swine flu, unless there are complications like hog cholera. On July 27, 2007, the Philippine National Meat Inspection Service (NMIS) raised a hog cholera "''red alert''" warning over Metro Manila and 5 regions of Luzon after the disease spread to backyard pig farms in Bulacan and Pampanga, even if these tested negative for the swine flu virus.<ref>
===Gender===
{{cite news
There is no gender predilection to the development of swine influenza.
|url=http://www.gmanews.tv/story/56805/DA-probes-reported-swine-flu-outbreak-in-N-Ecija
|title=DA probes reported swine flu 'outbreak' in N. Ecija
|publisher=Gmanews.tv
|date=
|accessdate=2009-04-25
}}</ref><ref>
{{cite news
|url=http://www.gmanews.tv/story/53014/Govt-declares-hog-cholera-alert-in-Luzon
|title=Gov't declares hog cholera alert in Luzon
|publisher=Gmanews.tv
|date=
|accessdate=2009-04-25
}}</ref>


===Outbreaks in humans===
===Race===
Swine flu has been reported numerous times as a zoonosis in humans, usually with limited distribution, rarely with a widespread distribution.  The 1918 flu pandemic in humans was associated with H1N1, thus may reflect a zoonosis either from swine to humans or from humans to swine.  Evidence available from that time is not sufficient to resolve this question.
There is no racial predilection to the development of swine influenza.
 
==== 1976 U.S. outbreak ====<!-- some incoming links anchor here -->
On February 5, 1976, an army recruit at Fort Dix said he felt tired and weak. He died the next day and four of his fellow soldiers were later hospitalized. Two weeks after his death, health officials announced that swine flu was the cause of death and that this strain of flu appeared to be closely related to the strain involved in the 1918 flu pandemic. Alarmed public-health officials decided that action must be taken to head off another major [[pandemic]], and they urged President Gerald Ford that every person in the U.S. be vaccinated for the disease.<ref>{{cite news |first=Harold M. |last=Schmeck |authorlink= |coauthors= |title=Ford Urges Flu Campaign To Inoculate Entire U.S. |url=http://select.nytimes.com/gst/abstract.html?res=F50A17FD3C5A167493C7AB1788D85F428785F9 |work=The New York Times |publisher= |date=March 25, 1976 |accessdate= }}</ref>
 
However, the [[vaccination]] program was plagued by delays and public relations problems. But on Oct. 1, 1976, the immunization program began and by Oct. 11, approximately 40 million people, or about 24% of the population, had received swine flu immunizations. That same day, three senior citizens died soon after receiving their swine flu shots and there was a media outcry linking the deaths to the immunizations, despite not having any positive proof.  According to science writer Patrick Di Justo, however, by the time the truth was known - that the deaths were not proven to be related to the vaccine - it was too late. "The government had long feared mass panic about swine flu -- now they feared mass panic about the swine flu vaccinations." This became a strong setback to the program.<ref name=DiJusto>[http://www.salon.com/env/feature/2009/04/28/1976_swine_flu/ "The Last Great Swine Flu Epidemic"], ''Salon.com'', April 28, 2009</ref>
 
There were reports of [[Guillain-Barré syndrome]], a paralyzing [[neuromuscular]] disorder, affecting some people who had received swine flu immunizations. As a result, Di Justo writes that "the public refused to trust a government-operated health program that killed old people and crippled young people." In total, less than 33 percent of the population had been immunized by the end of 1976. The National Influenza Immunization Program was effectively halted on Dec. 16.
 
Overall, about 500 cases of Guillain-Barré syndrome (GBS), resulting in death from severe pulmonary complications for 25 people, which, according to Dr. P. Haber, were probably caused by an immunopathological reaction to the 1976 vaccine. Other influenza vaccines have not been linked to GBS, though caution is advised for certain individuals, particularly those with a history of GBS.<ref>
{{cite journal
|title=Vaccines and guillain-barré syndrome
|author=Haber P, Sejvar J, Mikaeloff Y, Destefano F
|journal=Drug Saf
|year=2009
|volume=32
|issue=4
|pages=309–23.
|doi=10.2165/00002018-200932040-00005
|pmid=19388722
|doi_brokendate=2009-04-26
}}</ref><ref>
{{cite web
|title=Influenza / Flu Vaccine
|url=http://www.uis.edu/healthservices/immunizations/influenzavaccine.html
|publisher=University of Illinois at Springfield
|accessdate=26 April 2009
}}</ref>
 
==== 2009 swine flu outbreak ====
 
See also: [http://maps.google.com/maps/ms?ie=UTF8&hl=en&t=p&msa=0&msid=106484775090296685271.0004681a37b713f6b5950&ll=32.639375,-110.390625&spn=15.738151,25.488281&z=5 Live map of swineflu], [http://maps.google.com/maps/ms?ie=UTF8&hl=en&source=embed&msa=0&msid=109496610648025582911.0004686892fbefe515012&ll=53.14677,0.878906&spn=10.248613,19.775391&z=6 H1N1 live map]
The new strain of influenza involved in the 2009 swine flu outbreak strain is a reassortment of several strains of influenza A virus subtype H1N1 that are, separately, endemic in humans and in swine.  Preliminary genetic characterization found that the [[hemagglutinin]] (HA) gene was similar to that of swine flu viruses present in United States pigs since 1999, but the [[neuraminidase]] (NA) and [[matrix protein]] (M) genes resembled versions present in European swine flu isolates.  Viruses with this genetic makeup had not previously been found to be circulating in humans or pigs, but there is no formal national surveillance system to determine what viruses are circulating in pigs in the United States.<ref name="MMWR5815a5">
{{cite web
|url=http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5815a5.htm
|title=Swine influenza A (H1N1) infection in two children --- Southern California, March--April 2009
|date=22 April 2009
|publisher=[[Centers for Disease Control]]
|work=Morbidity and Mortality Weekly Report 
|volume=58 (Dispatch)
|issue=1-3
}}</ref>
 
The origins of this new strain remain unknown. One theory is that Asian and European strains traveled to Mexico in migratory birds or in people, then combined with North American strains in Mexican pig factory farms before jumping over to farm workers.<ref>David Kirby, [http://www.huffingtonpost.com/david-kirby/swine-flu-outbreak----nat_b_191408.html Swine Flu Outbreak – Nature Biting Back at Industrial Animal Production?&#93;, ''The Huffington Post'', 26 April 2009</ref>
 
[[Image:H1N1 map.png|400px|thumb|center|{{legend|#751012|Confirmed cases followed by death}}{{legend|#FF0000|Confirmed cases}}{{legend|#FFA900|Unconfirmed or suspected cases}} ]]
 
The earliest known human influenza A virus subtype H1N1 case was at a Mexican pig farm whose nearby neighbors had been complaining about the manure smell and flies.<ref>[http://www.timesonline.co.uk/tol/life_and_style/health/article6182789.ece Mexico outbreak traced to 'manure lagoons' at pig farm], Times Online, April 28, 2009</ref>
 
Edgar Hernandez, 4, was suffering from ordinary influenza but laboratory testing has since shown that he had contracted human influenza A virus subtype H1N1. The boy went on to make a full recovery.<ref>[http://www.timesonline.co.uk/tol/life_and_style/health/article6182789.ece Mexico outbreak traced to 'manure lagoons' at pig farm], Times Online, April 28, 2009</ref>
 
The Mexican health agency acknowledged that the original disease vector of the virus may have been flies multiplying in manure lagoons of pig farms near Perote, Veracruz, owned by Granjas Carroll,<ref>[http://www.jornada.unam.mx/2009/04/06/index.php?section=estados&article=030n1est Granjas Carroll provocó la epidemia de males respiratorios en Perote, según agente municipal&#93;, ''La Jornada'', 5 April 2009. {{es icon}}</ref> a subsidiary of Smithfield Foods.<ref>{{cite web |url=http://www.grist.org/article/2009-04-25-swine-flu-smithfield/ |title=Swine-flu outbreak could be linked to Smithfield factory farms, by Tom Philpott |publisher=Grist.org, 25 April 2009 |accessdate=2009-04-27}}</ref>
 
Dr. Anne Schuchat, interim Deputy Director for CDC Science and Public Health, said that the American cases were found to be made up of genetic elements from four different flu viruses &ndash; North American swine influenza, North American avian influenza, human influenza, and swine influenza virus typically found in Asia and Europe &ndash; "an unusually mongrelised mix of genetic sequences."<ref name="NewSci-20090426-dn17025">{{cite web|url=http://www.newscientist.com/article/dn17025-deadly-new-flu-virus-in-us-and-mexico-may-go-pandemic.html|title=Deadly new flu virus in US and Mexico may go pandemic|publisher=New Scientist|date=2009-04-26|accessdate=2009-04-26}}</ref> Pigs have been shown to act as a potential "mixing vessel" in which reassortment can occur between flu viruses of several species.<ref>{{cite web|title=New swine flu virus supports 'mixing vessel' theory|url=http://www.cidrap.umn.edu/cidrap/content/influenza/avianflu/news/dec2007swine.html|author=Robert Roos|date=2007-12-20}}</ref><ref>{{cite web|url=http://www.pnas.org/content/104/52/20949.abstract|title=Identification of H2N3 influenza A viruses from swine in the United States|journal=PNAS|date=2007-12-26|doi=10.1073/pnas.0710286104}}</ref> This new strain appears to be a result of [[reassortment]] of human influenza and swine influenza viruses, presumably due to [[superinfection]] in an individual human. Influenza viruses readily undergo reassortment because their [[genome]] is split between eight pieces of [[RNA]] (see [[Orthomyxoviridae]]).
 
The influenza A virus subtype H1N1 can adapt and spread more efficiently than previously known [[H1N1]] strains. Moreover, co-infection of [[H1N1]] swine flu and [[Oseltamivir]] resistant [[H1N1]] season flu can lead to acquisition of Influenza A virus subtype H274Y (H274Y) by the swine flu via [[recombination]] or reassortment.  Swine [[H1N1]] with human H1 and N1 have been reported. Moreover, the swine flu can also infect swine and acquire more [[polymorphisms]] that could lead to increased [[virulence]].
 
The 1918 [[pandemic]] strain has [[polymorphism]] from swine and human [[H1N1]] in all eight pieces of [[RNA]] gene segments.  Similar swapping of [[polymorphism]] in human co-infected with season and swine [[H1N1]] can lead to rapid [[evolution]].<ref>{{cite web|url=http://www.recombinomics.com/News/04220902/H1N1_CA_Swine_H2H.html|title=Human Transmission of Swine H1N1 in Southern California|date=2007-04-22}}</ref>


==References==
==References==

Revision as of 23:08, 21 February 2016

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Swine influenza usually occurs in outbreaks/pandemics, and the incidence may vary greatly from one year to another. The 2009 H1N1 global infection rate was 11% to 21%. During the 2009 swine influenza outbreak, the incidence in the USA was approximately 18,000 per 100,000 individuals (a total of 60 million cases) with approximately 265,000 hospitalizations reported. The worldwide case fatality rate is unknown, but is thought to range from 15,000 (initial reports) to 500,000 when patients with no healthcare access were counted. Individuals of all age groups may be affected by swine influenza. There is no gender or racial predilection to the development of swine influenza.

Epidemiology and Demographics

Incidence

  • Swine influenza usually occurs in outbreaks/pandemics, and the incidence may vary greatly from one year to another.
  • The 2009 H1N1 global infection rate was 11% to 21%.[1]
  • During the 2009 swine influenza outbreak, the incidence in the USA was approximately 18,000 per 100,000 individuals (a total of 60 million cases) with approximately 265,000 hospitalizations reported.[2]

Case-Fatality Rate

  • The exact case fatality rate is unknown.
  • During the 2009 swine influenza outbreak, initial reports stated that a total of 15,000-18,000 individuals died worldwide, the majority of whom were under 65 years of age.[3][4] Three years later, however, it was speculated that more than 280,000 - 500,000 individuals may have died due to 2009 swine influenza. The initial underestimation was thought to be caused by not counting individuals with no access to healthcare in developing countries.[5][6][7]

Age

  • Individuals of all age groups may be affected by swine influenza.[8]
  • Compared to the elderly, younger individuals are at higher risk of developing swine influenza. It is thought that older individuals may have a higher degree of cross-protection against influenza infection.[8]
  • Small children and the elderly are at higher risk of developing swine flu-related complications.

Gender

There is no gender predilection to the development of swine influenza.

Race

There is no racial predilection to the development of swine influenza.

References

  1. ↑ Roos, Robert (8 August 2011). "Study puts global 2009 H1N1 infection rate at 11% to 21%". CIDRAP. Retrieved 10 August 2011.
  2. ↑ "Press Briefing Transcripts CDC 2009 H1N1 Flu Media Briefing". CDC. Retrieved 21 Feb 2016. line feed character in |title= at position 27 (help)
  3. ↑
  4. ↑ "H1N1 Still A Pandemic, Says WHO". redOrbit. Retrieved 10 August 2010.
  5. ↑ Dawood FS, Iuliano AD, Reed C; et al. (September 2012). "Estimated global mortality associated with the first 12 months of 2009 pandemic influenza A H1N1 virus circulation: a modelling study". Lancet Infect Dis. 12 (9): 687–95. doi:10.1016/S1473-3099(12)70121-4. PMID 22738893.
  6. ↑ "First Global Estimates of 2009 H1N1 Pandemic Mortality Released by CDC-Led Collaboration". Centers for Disease Control and Prevention (CDC). 25 June 2012. Retrieved 3 July 2012.
  7. ↑ Goodenough, T. (26 June 2012). "Swine flu killed 250,000 - 15 TIMES the number of people reported, claims international study". Mail Online. Retrieved 3 July 2012.
  8. ↑ 8.0 8.1 Kaplan, Karen (18 September 2009). "Swine flu's tendency to strike the young is causing confusion". Los Angeles Times. Archived from the original on 19 September 2009. Retrieved 18 September 2009.
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