Epidemic :A clear excess in the number of cases of
Transcript of Epidemic :A clear excess in the number of cases of
Epidemic :A clear excess in the number of cases of a given disease (over the expected level) i.e in comparison with the expected level or what is expected in a given time period .
Expected level can be known by comparing with previous reports , If expected number was zero and we have two cases , it means an epidemic . Iraq is free from polio then the appearance of two cases of polio means an epidemic .We usually compare with average of the previous five years .
Every epidemic should be reported but not every one should be investigated , a case of HIV or cholera should be reported and investigated , while 30 cases of gastroenteritis do not need investigation.
Endemic – Persistent, usual,or expected health-related state or event in a defined population over a given period of time
• Pandemic – Epidemic affecting a large number of people, many countries, continents, or regions
Common source Tend to result in more cases occurring more rapidly
and sooner than host-to-host epidemics
Identifying and removing exposure to the common source typically causes the epidemic to rapidly decrease
Common source Examples
anthrax, traced to milk or meat from infected animals
botulism, traced to soil-contaminated food
and cholera traced to fecal contamination of food and water
Propagated Arise from infections being transmitted from one
infected person to another
Transmission can be through direct or indirect routes
Host-to-host epidemics rise and fall more slowly than common source epidemics
Disease transmission Disease transmission usually occurs by
direct, person-to-person contact (e.g., STDs)
fomite-borne (e.g., Hepatitis A spread by a contaminated eating utensil)
vehicle-borne (e.g., HIV/AIDS spread through needle sharing drug users)
vector-borne transmission (e.g., Malaria spread through mosquitoes)
Mixed epidemics Occurs when a common source epidemic is followed
by person-to-person contact and the disease is spread as a propagated outbreak
Example – Shigellosis occurred among a group of 3000 women attending a wedding festival. Over the next few weeks, subsequent generations of shigella cases spread by person-to-person transmission from festival attendees.