Question

1. Assume that the mosquito population across the southeast United States begins carrying the Zika virus. South Carolina legislators are concerned about the impact on pregnant women. A screening test (Test X) is required for all women of child-bearing age during annual appointments with their Ob/Gyn. The projected population to be screened in year 2020 is 100,000. State legislators want to know how many people will potentially need specialized medical care due to a positive test.

You have the 2018 testing data from Brazil that tells you the sensitivity of test X is 80.0% and the specificity is 99.5%. The estimated prevalence of Zika virus is 1.5 per 10,000 women of child-bearing age. Answer the following questions legislators may present at a hearing.

NOTE: For this and the next problem, write the terminology related to the question when it is not provided (e.g., if you are calculating a sensitivity, explicitly state that this is the sensitivity). Please show all your work.

1. Set-up the 2×2 table with the data given above. (9 points)

Zika Virus screening (Test X)	Zika Virus		Total
	+	-
+
-
Total

Answer 1

	Zika Virus	No Zika Virus	Total
Test X +	12	499.93	511.93
Test X -	3	99485.07	99488.07
Total	15	99985	100,000

sensitivity = 80%

specificity = 99.5%

prevalence = 1.5 per 10,000

Population = 100,000

People with Zika Virus = (1.5 / 10000) * 100000

People without Zika Virus = 100000 - 15 = 99985

People with positive test results with Zika Virus = sensitivity * People with Zika Virus

= 0.8 * 15 = 12

People with negative test results with Zika Virus = People with Zika Virus - People with positive test results with Zika Virus = 15 - 12 = 3

People with negative test results without Zika Virus = specificity * People without Zika Virus

= 0.995 * 99985 = 99485.07

People with positive test results without Zika Virus = People without Zika Virus - People with negative test results without Zika Virus

= 99985 - 99485.07 = 499.93

People with positive test results = 12 + 499.93 = 511.93

People with negative test results = 3 + 99485.07 = 99488.07