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[drake19]

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Question: 10,000 IV-drug-users. 1,000 turn out to be infected with HCV. During two years of follow-up 200 patients with HCV die. Also during follow-up 200 IVDU acquire HCV. What is the estimate of annual incidence of HCV over these two years.


Here is my question:
So i know how to calculate the numerator 200 new cases over 2 years = 200/2 = 100
How about the denominator for incidence - why is the answer 9,000?
Did they get the denominator by 10,000 - 200 (HCV death) + 200 (HCV new cases) = 9,000 IVDU at risk for HCV?

Answer by the way is: 100 / 9,000

Just confused about how to factor in deaths when calculating incidence

 

[Postictal Raiden]

Question: 10,000 IV-drug-users. 1,000 turn out to be infected with HCV. During two years of follow-up 200 patients with HCV die. Also during follow-up 200 IVDU acquire HCV. What is the estimate of annual incidence of HCV over these two years.


Here is my question:
So i know how to calculate the numerator 200 new cases over 2 years = 200/2 = 100
How about the denominator for incidence - why is the answer 9,000?
Did they get the denominator by 10,000 - 200 (HCV death) + 200 (HCV new cases) = 9,000 IVDU at risk for HCV?

Answer by the way is: 100 / 9,000

Just confused about how to factor in deaths when calculating incidence

incidence = # of new cases / # of people at risk. In this scenario, 9000, not 10,000, are at risk because 1000 already have HCV.

 

[drake19]

incidence = # of new cases / # of people at risk. In this scenario, 9000, not 10,000, are at risk because 1000 already have HCV.

yeah but how do you factor in the 200 people who died on followup and 200 new cases into the denominator

so is it 10,000 - 200 + 200 = 9,000?

 

[Postictal Raiden]

yeah but how do you factor in the 200 people who died on followup and 200 new cases into the denominator

so is it 10,000 - 200 + 200 = 9,000?

you don't. That's only a distractor. The 200 who died are part of the people who already had the infection, and you only worry about those who are susceptible to the infection.

 

[dorster]

you don't have to factor in the deaths because it says 200 people with HCV died. Those 200 people are among the 1,000 that you already pulled out by saying 10,000-1,000. So it doesn't change the denominator of 9000.

 

[drake19]

ok that makes sense