Question

An attack rate is an alternative incidence rate that is used when:

* A. describing the occurrence of food-borne illness or infectious diseases.

B. the population at risk increases greatly over a short time period. *

C. the disease rapidly follows the exposure during a fixed time period.

D. all of the above.

Answer 1

Attack rate is the number of people in a population that will contract (become ill) the disease when the disease free population is exposed to infectious agent in specific period of time. It is not a true rate. Formula for attack rate is:

Attack rate= Number of diseased/ill individuals after exposure to suspected agent/( Number of diseased/ill and non-diseased/Well individuals after exposure the suspected agent) X 100 (in specific time period)

In order for the attack rate to be used, there should be increased disease occurrence in an at-risk population over the short time period after exposure to the specific disease causing agent. If the disease occurrence rate does not increase, then attack rate cannot be used as both well and ill individuals remain the same.

Attack rate is used for acute diseases such as food borne diseases, infectious diseases that can lead to epidemics. Such acute diseases will only show increased occurrence over short periods of time. Further, the nature of the disease progression allows rapid progression of the disease after exposure to the causative agent during this short fixed specified time period. Chronic diseases will take a longer time to progress in the infected population and hence, cannot be studied in the short time period.

Right choice: D. All of the above.