Influenza epidemiology and demographics: Difference between revisions
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==Epidemiology and Demographics== | ==Epidemiology and Demographics== | ||
===Prevalence=== | |||
===Incidence=== | |||
===Gender=== | |||
===Age=== | |||
*Influenza viruses cause disease among persons in all age groups. | |||
*Rates of infection are highest among children, but the risks for complications, hospitalizations, and deaths from influenza are higher among persons aged 65 years and older, young children, and persons of any age who have medical conditions that place them at increased risk for complications from influenza. | |||
*During 1990--1999, estimated average rates of influenza-associated pulmonary and circulatory deaths per 100,000 persons were: | |||
:* 0.4-0.6 among persons aged 0-49 years | |||
:* 7.5 among persons aged 50-64 years | |||
:* 98.3 among persons aged 65 years and older. | |||
===Complications=== | |||
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===Seasonal variation=== | ===Seasonal variation=== | ||
{{further|[[Flu season]]}} | {{further|[[Flu season]]}} | ||
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New influenza viruses are constantly being produced by [[mutation]] or by [[reassortment]]. Mutations can cause small changes in the hemagglutinin and neuraminidase [[antigen]]s on the surface of the virus. This is called [[antigenic drift]], which creates an increasing variety of strains over time until one of the variants eventually achieves higher [[fitness (biology)|fitness]], becomes dominant, and rapidly sweeps through the human population – often causing an epidemic.<ref>{{cite journal | author = | title = Long intervals of stasis punctuated by bursts of positive selection in the seasonal evolution of influenza A virus | journal = Biol Direct | volume = 1 | issue = 1 | pages = 34 | year = 2006 | id = PMID 17067369}}</ref> In contrast, when influenza viruses re-assort, they may acquire new antigens — for example by reassortment between avian strains and human strains; this is called antigenic shift. If a human influenza virus is produced with entirely novel antigens, everybody will be susceptible and the novel influenza will spread uncontrollably, causing a pandemic.<ref>{{cite journal | last = Parrish | first = C | coauthors = Kawaoka Y | title = The origins of new pandemic viruses: the acquisition of new host ranges by canine parvovirus and influenza A viruses | journal = Annual Rev Microbiol | volume = 59 | issue = | pages = 553–86 | year = | id = PMID 16153179}}</ref> In contrast to this model of pandemics based on antigenic drift and shift, an alternative approach has been proposed where the periodic pandemics are produced by interactions of a fixed set of viral strains with a human population with a constantly-changing set of immunities to different viral strains.<ref>{{cite journal |author=Recker M, Pybus OG, Nee S, Gupta S |title=The generation of influenza outbreaks by a network of host immune responses against a limited set of antigenic types |url=http://www.pnas.org/cgi/content/full/104/18/7711 |journal=Proc Natl Acad Sci U S A. |volume=104 |issue=18 |pages=7711–7716 |year=2007 |pmid=17460037}}</ref> | New influenza viruses are constantly being produced by [[mutation]] or by [[reassortment]]. Mutations can cause small changes in the hemagglutinin and neuraminidase [[antigen]]s on the surface of the virus. This is called [[antigenic drift]], which creates an increasing variety of strains over time until one of the variants eventually achieves higher [[fitness (biology)|fitness]], becomes dominant, and rapidly sweeps through the human population – often causing an epidemic.<ref>{{cite journal | author = | title = Long intervals of stasis punctuated by bursts of positive selection in the seasonal evolution of influenza A virus | journal = Biol Direct | volume = 1 | issue = 1 | pages = 34 | year = 2006 | id = PMID 17067369}}</ref> In contrast, when influenza viruses re-assort, they may acquire new antigens — for example by reassortment between avian strains and human strains; this is called antigenic shift. If a human influenza virus is produced with entirely novel antigens, everybody will be susceptible and the novel influenza will spread uncontrollably, causing a pandemic.<ref>{{cite journal | last = Parrish | first = C | coauthors = Kawaoka Y | title = The origins of new pandemic viruses: the acquisition of new host ranges by canine parvovirus and influenza A viruses | journal = Annual Rev Microbiol | volume = 59 | issue = | pages = 553–86 | year = | id = PMID 16153179}}</ref> In contrast to this model of pandemics based on antigenic drift and shift, an alternative approach has been proposed where the periodic pandemics are produced by interactions of a fixed set of viral strains with a human population with a constantly-changing set of immunities to different viral strains.<ref>{{cite journal |author=Recker M, Pybus OG, Nee S, Gupta S |title=The generation of influenza outbreaks by a network of host immune responses against a limited set of antigenic types |url=http://www.pnas.org/cgi/content/full/104/18/7711 |journal=Proc Natl Acad Sci U S A. |volume=104 |issue=18 |pages=7711–7716 |year=2007 |pmid=17460037}}</ref> | ||
---> | |||
==References== | ==References== | ||
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[[Category:Disease]] | [[Category:Disease]] | ||
[[Category:Pulmonology]] | [[Category:Pulmonology]] | ||
[[Category:Influenza| ]] | [[Category:Influenza| ]] | ||
[[Category:Infectious disease]] | [[Category:Infectious disease]] | ||
[[Category:Primary care]] | [[Category:Primary care]] | ||
{{WH}} | {{WH}} | ||
{{WS}} | {{WS}} | ||
Revision as of 13:53, 28 October 2014
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Influenza epidemiology and demographics On the Web |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [2]
Overview
Epidemiology and Demographics
Prevalence
Incidence
Gender
Age
- Influenza viruses cause disease among persons in all age groups.
- Rates of infection are highest among children, but the risks for complications, hospitalizations, and deaths from influenza are higher among persons aged 65 years and older, young children, and persons of any age who have medical conditions that place them at increased risk for complications from influenza.
- During 1990--1999, estimated average rates of influenza-associated pulmonary and circulatory deaths per 100,000 persons were:
- 0.4-0.6 among persons aged 0-49 years
- 7.5 among persons aged 50-64 years
- 98.3 among persons aged 65 years and older.