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

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.

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.

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.

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

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%.

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.

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.

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.

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.