Biostat/epidemiology questions thread

[MudPhud20XX]

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Can anyone help me with the 2 questions below? I will post more biostat questions for discussion as time goes by. Many thanks in advance.

1. In a survey of 10,000 IV drug abusers in town A, 1,000 turn out to be infected with hep C and 500 infected with hep B. During two years of follow-up, 200 pts with hep C infection and 100 pts with hep B infection die. Also during follow-up, 200 IV drug abusers acquire hep C and 50 acquire hep B. Which of the following is the best estimate of the annual incidence of hep C infection in IV drug abusers in town A?

2. In a city having a population of 1,000,000 there are 300,000 women of childbearing age. The following stats are reported for the city in the year 2000:

Fetal deaths: 200
Live births: 5,000
Maternal deaths: 70

Calculate the maternal mortality rate in the city in the year 2000.

 

[aspiringmd1015]

MMR is the rate of maternal deaths/live births, so 70/5000

and for incedence, i believe its 200/8,500.

 

[student456]

Thanks for making this thread! I'm always having issues with the Incidence and Prevalence questions when it comes to new drug testing/disease/etc even after going over it few weeks ago. I need help in clearing this concept please.

 

[MudPhud20XX]

MMR is the rate of maternal deaths/live births, so 70/5000

and for incedence, i believe its 200/8,500.

You are right about MMR, but the incidence is not correct. Anyone?

 

[aspiringmd1015]

numerator has to be wrong, is it 9000 as the population at risk?

 

[Ophthoseidon]

That first question can be tough because it doesn't say if any of the hep B patients are co-infected with hep C (unless there is something I don't know). There were 10,000 to begin with, 1000 infected. There was a potential for 9,000 new cases at the beginning of the time interval but 100 people died who had hep B, which were potential cases for hep C, so maybe the denominator would be 8,900? There are 200 cases over 2 years, so if you are looking for annual, maybe the incidence is 100/8900? I'm sure that's not the exact number because some of those that died during the 2 years weren't at the beginning, etc. But I'm not really not sure how to do it otherwise without calculating person-years which is ridiculously tedious at best and we don't have that data lol. Could anyone enlighten me?

 

[NeuroMaster316]

I think incidence here is related to person-time but I forgot how to calculate it, give me a year till I take the med version of epi lol
EDIT: Think I got it

You have 9000 at risk since of the 10 000 you already had 1000 infected. You have 200 NEW cases in TWO years so a 100 in one year so that's your numerator. So the answer would be 100/9000
At first I thought the death numbers should be taken into account but then again the whole study spanned 2 years apparently so it doesn't matter cause you want the population at risk and those at risk are 9000.
I think at first I got mixed up with the incidence density rate which uses a person-time relation in the denominator but here it's absent so I'm fairly certain of the answer.

 

[NeuroMaster316]

Also maternal mortality rate is maternal deaths/women capable of bearing children so : 70/300 000
Damn this took me back a couple of years lol

 

[MudPhud20XX]

I think incidence here is related to person-time but I forgot how to calculate it, give me a year till I take the med version of epi lol
EDIT: Think I got it

You have 9000 at risk since of the 10 000 you already had 1000 infected. You have 200 NEW cases in TWO years so a 100 in one year so that's your numerator. So the answer would be 100/9000
At first I thought the death numbers should be taken into account but then again the whole study spanned 2 years apparently so it doesn't matter cause you want the population at risk and those at risk are 9000.
I think at first I got mixed up with the incidence density rate which uses a person-time relation in the denominator but here it's absent so I'm fairly certain of the answer.

Good job man. Good discussion guys. I'll post some more questions later.