Microbiology question: In a study on the relationship between oral contraceptive
ID: 71910 • Letter: M
Question
Microbiology question: In a study on the relationship between oral contraceptives (OCs) and urinary tract infections, 500 women who use CO and 3000 women who do not use OCs were were monitored over a period of the three years.
4. What is the incidence rate for the 3 year period among the women who use OCs?
5. What is the relative risk linked to the use of OCs and urinary tract infections?
6. What is the odds ratio as it relates to urinary tract infections?
7. What percentage of urinary tract infections could have been avoided?
8. How many cases of urinary tract infections associated with the use of OCs are expected per year in a population of 10 000 people of which 55% are women of which 20% use OCs?
Years Use OCs Dont use OCs 1 15 35 2 30 70 3 20 33Explanation / Answer
4. The incidence rate for the 3 year period among the women who use OCs:
INCIDENCE RATE =[(new cases occuring during a given time period)/(population at risk during same time period]X10n
Population at risk= 500+3000=3500 and new cases= 15+30+20=65
Incidence rate=(65/3500 )x105 =0.018 x105
5. Relative risk calculation:
Relative risk = (A/A+C)/ (B/B+D) =(138/3000)/ (65/500) =0.046/0.13 =0.354
6. Odd ratio= AD/BC =60030/186030 =0.323
7. percentage of urinary tract infections could have been avoided
138-65= 73
Among 3000 women who do not use OCs 138 have been infected and among 500 women who use OCs 65 have been infected.So if all women have taken OCs at least 73 cases could have been avoided.
So the required % =[73/3000] x 100 =2.433 %
8. In a population of 10 000 people of which 55% are women of which 20% use OCs.
So, Number of women =55% of 10000 =5500
Number of women who use OCs =20% of 5500=1100
In a population of 3500, cases of urinary tract infections associated with the use of OCs per year is 21.66 (approx)
So,in a population of 10,000, cases of urinary tract infections associated with the use of OCs per year is = [21.66/3500] x 10000 =61.88
EXPOSED NONEXPOSED TOTAL DISEASE 138 [A] 65 [B] 203 NO DISEASE 2862 [C] 435 [D] 3297 TOTAL 3000 500