1. Biology 261 Microbiology Medgar Evers College, CUNY
Epidemiology Chapter 19
Biology 261
Microbiology
Medgar Evers College, CUNY

2. Epidemiology
The study of the spread, control, and prevention of disease in a population.
An epidemiologist collects and compiles data to describe disease outbreaks and come up with strategies to prevent future outbreaks and protect the population.

3. terminology
contagious disease- a disease that can be transmitted from one host to another.
A chain of events must occur in order to spread the disease.
A- the pathogen must have a suitable place to live. This natural habitat is called the reservoir of infection.

4. The reservoir can be an animal, or an environment such as water or soil.
B- A pathogen must leave the reservoir through a body orifice or be shed from any surface. We call this the portal of exit.
C- the pathogen must be transmitted to the next host through direct contact or via contaminated food, water or air.

5. D- The portal of entry is the orifice or surface that the pathogen enters the next host.

6. Rate factors Rate of disease- the proportion of a population infected.
Attack rate- the number of cases developing in a group who were exposed to the agent.
Example; If 200 people attended a picnic and 20 came down with food poisoning, then the attack rate is 10%.

7. Morbidity rate- the number of cases of an illness in a given time period divided by the population at risk.
Mortality rate- the percentage of population that dies from a disease.
Incidence- the number of new cases in a specific time period in a given population at risk.

8. Prevalence- the number of total existing cases both old and new in a population at risk.
Endemic disease- a disease that is constantly present in a population such as the cold and flu.

9. Epidemic- an unusually large number of cases in a population
Pandemic- the epidemic spreads worldwide.
Outbreak- a cluster of cases occurring during a brief period of time and affecting a specific population.

10. III. The most important steps in preventing health care associated infections are to first recognize their occurrence and then establish policies to prevent both their development and spread.