Epidemiology of Influenza

1. Epidemiology of Influenza

2. The Flu Basics • The flu is contagious and can range from mild to deadly • Each year between 5% and 20% of the US population contracts the flu • During pandemics the rate is between 25% and 50% • Annually there are more than 200,000 hospitalizations due to the flu • Approximately 36,000 people die a year from the flu in the US • Most of which are the elderly, the young, and people with certain health conditions

3. The Flu is Unpredictable • Outbreaks have been known to occur in three patterns • pandemics every 30 to 40 years • high mortality • epidemics much more frequently • lower mortality • mild sporadic outbreaks

4. Morbidity and Mortality • Recognized since at least the time of Elizabeth I of England • Hard to quantify morbidity and mortality since exact diagnosis relies on laboratory confirmation

5. Morbidity • Quantification of morbidity has required different approaches • community and family studies have made major contributions • Morbidity is most pronounced in children and young adults • the diseases are self-limited, they are often severe • Each year must be considered an influenza year in lieu of the fact that the size of the outbreak varies since it can be documented annulally

6. Mortality • Excess mortality has been documented since 1889 • Various methods have been developed to provide estimates of the mortality associated with influenza • usually predicated on establishing expected baseline rates of mortality • deaths in excess of these rates are calculated and attributed to the circulating influenza virus • Groups at high risk of mortality have been defined as the elderly, those with chronic conditions, and those in institutions (prison)

7. http://nmhm.washingtondc.museum/collections/archives/agalleries/1918flu/Reeve3203.jpghttp://nmhm.washingtondc.museum/collections/archives/agalleries/1918flu/Reeve3203.jpg

8. Vectors (bird, mammalian, human) http://www.hopkins-cepar.org/bin/c/e/bird_flu_transmission_chart.gif

9. Transmission • Influenza is highly contagious • it is easily transmitted through contact with droplets from the nose and throat of an infected person released while coughing or sneezing • The disease infects the respiratory tract • It often breaks out as an epidemic • It can quickly spreads from town to town and country to country with the help of modern transportation • Epidemics generally exist in an area for a period of four to six weeks before it eases off • Influenza can make many people ill in a short period of time • onset of symptoms range from 18 to 72 hours.

10. Emerging Flu (H5N1) • subtype of Influenza A virus • “H” in H5 refers to the type of hemagglutinin antigen on the viral envelope • N1 refers to the neuroaminidase enzyme that helps get through the mucal layer and in the budding of new virus particles • H5N1 emerged in humans in 1997

11. H5N1 ~ The Avian Flu • virus subtype that occurs mainly in birds • highly contagious among birds – can even be deadly • H5N1 virus does not usually infect people, but infections with these viruses have occurred in humans. • Most of these cases have resulted from people having direct or close contact with H5N1-infected poultry or H5N1-contaminated surfaces.

12. http://images.chron.com/content/news/photos/05/05/08/avian1.jpghttp://images.chron.com/content/news/photos/05/05/08/avian1.jpg

13. http://ec.europa.eu/health/ph_threats/com/Influenza/images/influenza.jpghttp://ec.europa.eu/health/ph_threats/com/Influenza/images/influenza.jpg

14. Sources • http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3591814&dopt=Abstract • http://www.globalsecurity.org/security/ops/hsc-scen-3_flu-pandemic-deaths.htm • http://www.stanford.edu/group/virus/uda/index.html • Black, J., 2002 Microbiology: Principles and Explorations. 5th ed. New Jersey: John Wiley and Sons, Inc., 762 p. • http://www.cdc.gov/flu/avian/gen-info/facts.htm • http://www.cdc.gov/flu/avian/gen-info/spread.htm