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#1
08-05-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,866 Threads: 149 Thanked 2,249 Times in 1,096 Posts Reputation: 2269
incidence

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. 1000/1,000,000

D. 2500/1,000,000

E. 10,000/1,000,000

#2
08-05-2012
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i would say C
#3
08-05-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,866 Threads: 149 Thanked 2,249 Times in 1,096 Posts Reputation: 2269

Explanation:

The correct answer is C. The incidence of a disease is given by the number of new cases in a given period
divided by the total population. In this case, this is equal to 1000/1,000,000.

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).

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 E).

#4
08-08-2012
 USMLE Forums Scout Steps History: CS Only Posts: 18 Threads: 8 Thanked 12 Times in 1 Post Reputation: 22

Quote:
 Originally Posted by Novobiocin 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. 1000/1,000,000 D. 2500/1,000,000 E. 10,000/1,000,000

i have a doubt . To calculate incidence , do we need to include people who are dead or already have the disease !! I mean isnt incidence New cases/Potential cases.

like denominator here should ve been according to this concept ,

1,00,000 -[(10,000 + 2500)] = 87500

so incidence = 1000/87500
#5
08-08-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 590 Threads: 31 Thanked 1,270 Times in 416 Posts Reputation: 1294

Quote:
 Originally Posted by Shankar i have a doubt . To calculate incidence , do we need to include people who are dead or already have the disease !! I mean isnt incidence New cases/Potential cases. like denominator here should ve been according to this concept , 1,00,000 -[(10,000 + 2500)] = 87500 so incidence = 1000/87500
Even if you take out everyone who already has it and the people who die, you are still left with an incidence of 1,000/987,500. That equals 987.5/1,000,000, which is much closer to 1,000/1,000,000 than any of the other answers. So C is still the best answer...

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