There were 100 new cases of syphilis last year in a given population of 100,000 people. at that time, 500 people in this population already had syphilis. the incidence of syphilis in this population is . 100 per 100,000b. 500 per 100,000c. 1000 per 100,000d. 5000 per 100,000

a) 100 per 100,000

Explanation:

The term Incidence refers to the number of individuals who develop a specific disease during a particular time period (a month, a year, etc) in a certain population. Thus, incidence refers to the new cases that present in a population over the course of some specific amount of time.

In this case, there were 100 NEW cases of syphilis last year in a population of 100,000 people.

Since incidence refers to only the new cases of a disease we really don't need to focus on the 500 people who already had syphilis.

Thus, the incidence of syphilis in this population is a) 100 per 100,000