A cohort study was conducted with 9,488 residents of Broncoville examining the i

Question

A cohort study was conducted with 9,488 residents of Broncoville examining the impact of floor of residence on exposure to West Nile Virus (WNV). Residents were divided into those living on floors 4 or lower (5,080) or those living on floors 5 or higher (4,408). Blood was drawn for antibody testing to WNV. On the lower floors 47 persons were antibody positive and on the upper floors, 7 persons were antibody positive. Using the higher floors as the “exposed” group, develop a 2 x 2 table, showing the relative risk of residence on the upper floors?

1. Calculate the incidence rate per 10,000 persons for people living on floor 5 or higher

2. Calculate the incidence rate per 10,000 persons for people living on floor 4 or lower

3. Calculate the relative risk of developing antibodies to WNV among residents on the upper floors

Explanation / Answer

Answer.

1.

Incidence rate for upper floor people = present / total = (7/4408)*100 % = 0.158802178 %

Hence, for 10000 people,

Incidence prone people = 0.158802178 * 10000 = 15.8 OR ~ 16.

2.

Incidence rate for lower floor people = present / total = (47/5080)*100 % = 0.92519685 %

Hence, for 10000 people,

Incidence prone people = 0.92519685 * 10000 = 92.5 OR ~ 93.

3.

Relative Risk = rate of exposed/ rate of non-exposed = 0.158802178/0.92519685 =  0.171641503.

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