Influenza epidemiology and demographics: Difference between revisions

Jump to navigation Jump to search
VisualWikitext
Line 75: Line 75:


==Worldwide Influenza==
==Worldwide Influenza==
<!---
===Seasonal variation===
{{further|[[Flu season]]}}
[[Image:H5n1 spread with regression.png|thumb|center|300px|Cumulative Confirmed Human Cases of H5N1.<ref name=WHOH5N1data>[http://www.who.int/csr/disease/avian_influenza/country/en/ WHO Confirmed Human Cases of H5N1] Data published by WHO Epidemic and Pandemic Alert and Response (EPR). Accessed 24 Oct. 2006</ref> The regression curve for deaths is shown extended through the end of November 2006.]]
Influenza reaches peak prevalence in winter, and because the Northern and Southern Hemisphere have winter at different times of the year, there are actually two different flu seasons each year. This is why the [[World Health Organization]] (assisted by the [[National Influenza Centers]]) makes recommendations for two different vaccine formulations every year; one for the Northern, and one for the Southern Hemisphere.<ref name= WHOrecommendation>[http://www.who.int/csr/disease/influenza/2007northreport.pdf  Recommended composition of influenza virus vaccines for use in the 2006–2007 influenza season] WHO report 2006-02-14. Accessed [[19 October]] [[2006]].</ref>
It remains unclear why outbreaks of the flu occur seasonally rather than uniformly throughout the year. One possible explanation is that, because people are indoors more often during the winter, they are in close contact more often, and this promotes transmission from person to person. Another is that cold temperatures lead to drier air, which may dehydrate mucus, preventing the body from effectively expelling virus particles. The virus may also survive longer on exposed surfaces (doorknobs, countertops, etc.) in colder temperatures.  Increased travel and visitation due to the Northern Hemisphere winter holiday season may also play a role.<ref name = "NPR2003-12-17">[http://www.npr.org/templates/story/story.php?storyId=1551913 Weather and the Flu Season] NPR Day to Day, [[December 17]] [[2003]]. Accessed, [[19 October]] [[2006]]</ref> However, seasonal changes in infection rates are also seen in tropical regions and these peaks of infection are seen mainly during the rainy season.<ref>Shek LP, Lee BW. "Epidemiology and seasonality of respiratory tract virus infections in the tropics." ''Paediatr Respir Rev.'' 2003 Jun;4(2):105–11. PMID 12758047</ref> Seasonal changes in contact rates from school-terms, which are a major factor in other childhood diseases such as [[measles]] and [[pertussis]], may also play a role in flu.  A combination of these small seasonal effects may be amplified by "dynamical resonance" with the endogenous disease cycles.<ref>Dushoff J, Plotkin JB, Levin SA, Earn DJ. "Dynamical resonance can account for seasonality of influenza epidemics." ''Proc Natl Acad Sci U S A.'' [[30 November]][[2004]];101(48):16915–6. PMID 15557003</ref> [[H5N1]] exhibits seasonality in both humans and birds.<ref name=WHOH5N1data/>
An alternative hypothesis to explain seasonality in influenza infections is an effect of [[vitamin D]] levels on immunity to the virus.<ref>{{cite journal | last = Cannell | first = J | coauthors = Vieth R, Umhau J, Holick M, Grant W, Madronich S, Garland C, Giovannucci E | title = Epidemic influenza and vitamin D | journal = Epidemiol Infect | volume = 134 | issue = 6 | pages = 1129–40 | year = 2006 | id = PMID 16959053}}</ref> This idea was first proposed by Robert Edgar Hope-Simpson in 1965.<ref>{{cite journal | last = HOPE-SIMPSON | first = R | title = The nature of herpes zoster: a long-term study and a new hypothesis | journal = Proc R Soc Med | volume = 58 | issue = | pages = 9–20 | year = | id = PMID 14267505}}</ref> He proposed that the cause of influenza epidemics during winter may be connected to seasonal fluctuations of vitamin D, which is produced in the skin under the influence of solar (or artificial) [[ultraviolet|UV radiation]]. This could explain why influenza occurs mostly in winter and during the tropical rainy season, when people stay indoors, away from the sun, and their vitamin D levels fall. Furthermore, some studies have suggested that administering [[cod liver oil]], which contains large amounts of vitamin D, can reduce the incidence of respiratory tract infections.<ref name = "Linday2004">{{cite journal | last = Linday | first = L | coauthors = Shindledecker R, Tapia-Mendoza J, Dolitsky J | title = Effect of daily cod liver oil and a multivitamin-mineral supplement with selenium on upper respiratory tract pediatric visits by young, inner-city, Latino children: randomized pediatric sites | journal = Ann Otol Rhinol Laryngol | volume = 113 | issue = 11 | pages = 891–901 | year = 2004 | id = PMID 15562899}}</ref>
===Epidemic and pandemic spread===
{{further|[[Influenza pandemic]], [[Spanish flu]]}}
As influenza is caused by a variety of species and strains of [[virus]]es, in any given year some strains can die out while others create [[epidemic]]s while yet another strain can cause a [[pandemic]]. Typically, in a year's normal two [[flu season]]s (one per hemisphere) there are between three and five million cases of severe illness and up to 500,000 deaths worldwide, which by some definitions is a yearly influenza epidemic.<ref>[http://www.who.int/mediacentre/factsheets/fs211/en/ Influenza] WHO Fact sheet N°211 revised March 2003. Accessed [[22 October]] [[2006]]</ref>  Although the incidence of influenza can vary widely between years, approximately 36,000 deaths and more than 200,000 hospitalizations are directly associated with influenza every year in America.<ref>{{cite journal | last = Thompson | first = W | coauthors = Shay D, Weintraub E, Brammer L, Cox N, Anderson L, Fukuda K | title = Mortality associated with influenza and respiratory syncytial virus in the United States | url=http://jama.ama-assn.org/cgi/content/full/289/2/179 | journal = JAMA | volume = 289 | issue = 2 | pages = 179–86 | year = 2003 | id = PMID 12517228}}</ref><ref>{{cite journal | last = Thompson | first = W | coauthors = Shay D, Weintraub E, Brammer L, Bridges C, Cox N, Fukuda K | title = Influenza-associated hospitalizations in the United States | url= http://jama.ama-assn.org/cgi/content/full/292/11/1333 | journal = JAMA | volume = 292 | issue = 11 | pages = 1333–40 | year = 2004 | id = PMID 15367555}}</ref><ref>[http://www.niaid.nih.gov/factsheets/flu.htm Flu factsheet] National Institute of Allergy and Infectious Diseases Accessed 22 Dec 2006</ref> Every ten to twenty years a pandemic occurs, which infects a large proportion of the world's population, and can kill tens of millions of people (see history section).
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 &ndash; 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==

Revision as of 14:32, 28 October 2014

Influenza Microchapters

Home

Patient Information

Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Influenza from other Diseases

Epidemiology and Demographics

Risk Factors

Natural History, Complications and Prognosis

Diagnosis

History and Symptoms

Physical Examination

Laboratory Findings

Chest X Ray

Other Diagnostic Studies

Treatment

Medical Therapy

Primary Prevention

Cost-Effectiveness of Therapy

Future or Investigational Therapies

Case Studies

Case #1

Influenza epidemiology and demographics On the Web

Most recent articles

Most cited articles

Review articles

CME Programs

Powerpoint slides

Images

American Roentgen Ray Society Images of Influenza epidemiology and demographics

All Images
X-rays
Echo & Ultrasound
CT Images
MRI

Ongoing Trials at Clinical Trials.gov

US National Guidelines Clearinghouse

NICE Guidance

FDA on Influenza epidemiology and demographics

CDC on Influenza epidemiology and demographics

Influenza epidemiology and demographics in the news

Blogs on Influenza epidemiology and demographics

Directions to Hospitals Treating Influenza

Risk calculators and risk factors for Influenza epidemiology and demographics

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [3]; Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [4]

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:[1]
  • 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

Influenza in the United States

National and Regional Summary of Select Surveillance Components

Data cumulative since September 28, 2014 (week 40) [2]
HHS Surveillance Regions Out-patient ILI† % positive for flu‡ Number of jurisdictions reporting regional or widespread activity§ 2009 H1N1 Type A (H3) Type A
(Subtyping not performed) 		Type B Pediatric Deaths
Nation Normal 4.8% 1 of 54 7 267 405 392 1
Region 1 Normal 1.6% 0 of 6 0 8 8 4 0
Region 2 Elevated 1.1% 0 of 4 1 17 17 11 0
Region 3 Normal 1.7% 0 of 6 0 16 16 69 0
Region 4 Normal 8.0% 0 of 8 0 56 290 246 1
Region 5 Normal 2.1% 0 of 6 3 28 15 12 0
Region 6 Normal 4.3% 0 of 5 2 32 26 69 0
Region 7 Normal 1.9% 0 of 4 0 12 15 9 0
Region 8 Normal 1.2% 0 of 6 0 15 5 6 0
Region 9 Normal 3.2% 1 of 5 1 27 27 19 0
Region 10 Normal 5.5% 0 of 4 0 56 4 7 0

*HHS regions (Region 1 CT, ME, MA, NH, RI, VT; Region 2: NJ, NY, Puerto Rico, US Virgin Islands; Region 3: DE, DC, MD, PA, VA, WV; Region 4: AL, FL, GA, KY, MS, NC, SC, TN; Region 5: IL, IN, MI, MN, OH, WI; Region 6: AR, LA, NM, OK, TX; Region 7: IA, KS, MO, NE; Region 8: CO, MT, ND, SD, UT, WY; Region 9: AZ, CA, Guam, HI, NV; and Region 10: AK, ID, OR, WA).
† Elevated means the % of visits for Influenza-like illness (ILI) is at or above the national or region-specific baseline.
‡ National data are for current week; regional data are for the most recent three weeks.
§ Includes all 50 states, the District of Columbia, Guam, Puerto Rico, and U.S. Virgin Islands

Number of Influenza-Associated Pediatric Deaths by Week of Death: 2011-2012 season to present
Image obtained from CDC [1]
Weekly Influenza Activity Estimates Reported by State (Oct 2014)
Image obtained from CDC [2]

Worldwide Influenza

References

  1. ↑ "CDC Hospitalizations and Deaths from Influenza".
  2. ↑ "CDC Weekly U.S. Influenza Surveillance Report".

Template:WH Template:WS

Retrieved from "https://www.wikidoc.org/index.php?title=Influenza_epidemiology_and_demographics&oldid=1036976"