Prevalence
Definition: Prevalence measures the proportion of the population infected by a disease at a given time.
Prevalence can be calculated by using the following formula:
[(Number of existing cases (old and new)] / (Total Population)
Example: What is the prevalence of Lassa fever in airplane passengers? The passengers in the rows of the airplane shown here make up the total population.
Prevalence of Lassa fever in 5 rows of this airplane:
(1 case of Lassa fever) / (45 passengers) = 0.02 or 2%
Source: CDC - MMWR 53(38);897-7
