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#1
02-06-2012
 USMLE Forums Master Steps History: --- Posts: 1,203 Threads: 180 Thanked 1,254 Times in 441 Posts Reputation: 1268
the incidence of HIV disease

Q. In a city with a population of 1,000,000, 10,000 individuals have HIV disease. There are 1000 new cases of HIV disease and 200 deaths each year from the disease. There are 2500 deaths per year from all causes. Assuming no net emigration from or immigration to the city, the incidence of HIV disease in this city is given by which of the following?
A. 200/1,000,000
B. 800/1,000,000
C. 1000/990,000
D. 2500/1,000,000
E. 10,000/990,000
F. 10,000/1,000,000
 The above post was thanked by: docord (02-08-2012)

#2
02-06-2012
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Ans ........C..........
#3
02-08-2012
 USMLE Forums Master Steps History: --- Posts: 1,203 Threads: 180 Thanked 1,254 Times in 441 Posts Reputation: 1268

The answer is C.

The incidence of a disease is given by the number of new cases in a given period divided by the total susceptible population. In this case, this is equal to 1000/990,000.
The disease-specific mortality rate is the number of deaths per year from a specific disease divided by the population; in this case, 200/1,000,000 (choice A).
The rate of increase of a disease is given by the number of new cases per year, minus the number of deaths (or cures) per year, divided by the total population. Since there is yet no cure for HIV disease, the number of cures is 0. In this case, the rate of increase is (1000-200)/1,000,000 = 800/1,000,000 (choice B).
The crude mortality rate is given by the number of deaths from all causes, divided by the population; in this case, 2500/1,000,000 (choice D). 10,000/990,000 (choice E) is a distracter.
The prevalence of a disease is defined as the number of cases of the disease at a given time divided by the total population. In this case, it would be 10,000/1,000,000 (choice F).
 The above post was thanked by: Master shifu (02-08-2012)

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