Part 1

A hypothetical study of pulmonary tuberculosis was conducted in a rural town. All persons in the town were examined at two time points. The first was the beginning of the study. The second was 2-years later. The results are given in the following table:

Table 1

Results of the 1st examination	Number of persons	Number of new cases
With culture-positive case	500	10
Without culture-positive case	10,000	10

1. What is the incidence of new cases per 1000 person-years that had a culture-positive case during the 1st survey?
2. What is the incidence of new cases per 1000 person-years that did not have a culture-positive case during the 1st survey?
3. What is the relative risk of acquiring TB with a culture-positive case compared with a without culture positive TB? What is your interpretation of the risk?