Question

Consider a class with 100 enrolled students. None of the students were ill at the beginning of the school year. On September 30, a total of five students reported having gastroenteritis. All continued to be ill on October 1 but all five recovered in 3 days. On October 14, another three students developed gastroenteritis. All of these students continued to be ill on October 15, but all three recovered 5 days later. In this example, assume that a person cannot get gastroenteritis more than once.
A. Calculate the pre-valence of gastroenteritis in the class on October 1.
B. Calculate the pre-valence of gastroenteritis in the class on October 30.
C. Calculate the cumulative incidence of gastroenteritis in the class during the month of October.

Answer 1

Answer:

A. Calculate the prevalence of gastroenteritis in the class on October 1.

• 5%

B. Calculate the prevalence of gastroenteritis in the class on October 30.

• 0%

C. Calculate the cumulative incidence of gastroenteritis in the class during the month of October.

• 3.16%

Step-by-step explanation:

Prevalence is calculated using the following formula:

(number of sick people / total number of people measured) x 100%

October 1 = (5 / 100) x 100% = 5%

October 30 = (0 / 100) x 100% = 0%

Cumulative = [3 / (100 - who got sick on September)] x 100% =  (3/95) x 100% = 3.16%

Since 5 students got sick during September, they cannot be included in the cumulative statistics for October. This means that the cumulative denominator will be 95, not 100.