Question

Two surveys were performed, 12 months apart, in the same community. Of 5,000 people surveyed for the first time, 25 had antibodies to histoplasmosis. Twelve months later, 35 had antibodies, including the original 25.

a. Calculate the prevalence of people with histoplasmosis antibodies at the first survey.
b. Now calculate the prevalence of people with histoplasmosis in the second survey, and compare this prevalence with the 1-year incidence (calculate rates per 1,000).

Answer 1

The prevalence of histoplasmosis antibodies increased from 5 per 1000 in the first survey to 7 per 1000 in the second. The 1-year incidence rate was 2 per 1000, indicating that new cases occurred within that year.

Step-by-step explanation:

To calculate the prevalence of people with histoplasmosis antibodies at the first survey, we use the formula: Prevalence = (Number of people with antibodies / Total number of people surveyed) × 1000.

a. For the first survey, the prevalence is (25 / 5000) × 1000 = 5 per 1000 people.

b. For the second survey, the prevalence is (35 / 5000) × 1000 = 7 per 1000 people. To compare this with the 1-year incidence, we should only consider the new cases. There were 35 - 25 = 10 new cases of antibody detection. Therefore, the 1-year incidence rate is (10 / 5000) × 1000 = 2 per 1000 people.

The prevalence in the second survey is higher than in the first, indicating more people have been exposed to histoplasmosis over time. However, the 1-year incidence rate gives us the rate at which new exposures occurred within that year.

Answer 2

a. The prevalence of people with histoplasmosis antibodies at the first survey is 0.5%. b. To calculate the prevalence of people with histoplasmosis in the second survey, divide the number of people with antibodies in the second survey by the total number of people surveyed in the second survey and multiply by 100. To calculate the 1-year incidence rate, subtract the number of people with antibodies from the second survey by the number of people with antibodies from the first survey.

Step-by-step explanation:

a. To calculate the prevalence of people with histoplasmosis antibodies at the first survey, divide the number of people with antibodies (25) by the total number of people surveyed (5,000) and multiply by 100 to get the percentage.

Prevalence = (25 / 5,000) * 100 = 0.5%.

b. To calculate the prevalence of people with histoplasmosis in the second survey, divide the number of people with antibodies in the second survey (35) by the total number of people surveyed in the second survey and multiply by 100.

Prevalence = (35 / total number of people surveyed in the second survey) * 100.

To calculate the 1-year incidence rate, subtract the number of people with antibodies from the second survey (35) by the number of people with antibodies from the first survey (25).

1-Year Incidence Rate = (Number of new cases / total number of people surveyed in the second survey) * 1000.