Assignment:
Preventing Perinatal Transmission of HIV
Human immunodeficiency virus (HIV) is the virus that causes acquired immunodeficiency syndrome (AIDS), a fatal disease. HIV is spread through the exchange of body fluids by sexual intercourse; by exposure to infected blood and blood products, tissues and organs, either directly (person to person) or indirectly by coming in contact with contaminated needles; and by transmission from mother to child.
Since 1992 the incidence of pediatric AIDS cases (not just HIV-positive cases) in the United States has dropped significantly from more than 800 reported cases in 1992 to 175 reported cases in 2001 (see CDC, Pediatric AIDS Surveillance resource page, available at www.cdc.gov/hiv/graphics/pediatri.htm). Of these 175 infants, 86% contracted the virus from their mother, 1% contracted the virus through blood or blood products, and the method of acquisition in the last 13% was unknown. The significant drop in these cases was, at least in part, a result of the use of antiviral drugs given to pregnant HIV-positive women to deter the virus from reproducing in the women's bodies. If the viral count stays low within a woman, she will have a smaller chance of passing it on to her unborn fetus.
Pregnant women who are HIV positive are also advised to have cesarean births and not to breast-feed in order to reduce the chances of passing on the virus during birth or through breast milk, respectively. These preventive measures have been credited with significantly reducing HIV transmission from mother to child, which has resulted in the significant decrease in pediatric AIDS cases.
However, these measures could be taken only if pregnant women were aware of their HIV status, and testing for HIV is not something that many pregnant women think about. Although 175 reported cases in 2001 represent a significant drop from more than 800 cases in 1992, the
numbers could drop even further if more women who were pregnant were tested for HIV early in their pregnancy and took the protective measures for their unborn fetus mentioned previously. The Centers for Disease Control and Prevention (CDC) estimates that each year there are between 280 and 370 cases of HIV transmission from the mother to the child (see CDC, Revised recommendations for HIV screening of pregnant women, available at www.cdc.gov/mmwr/PDF/RR/RR5019.pdf). These numbers could be further reduced.
Part I
1. What could be done to get more pregnant women tested for HIV? Why would this be a very difficult task?
2. Some states have adopted policies for pregnant women to get HIV counseling and to get tested for the virus. Currently there are three methods that have been adopted by different states. One method is called the opt-in approach, in which pregnant women receive HIV counseling when seeking prenatal care and voluntarily choose to get tested. Another method is the opt-out approach, in which pregnant women also receive HIV counseling when seeking prenatal care and get tested for HIV, but they have the choice to opt out of getting tested. Finally, some states have a mandatory newborn testing policy, in which all newborns are tested for HIV no more than 48 hours after their birth.
Which method do you believe would be the most effective? Which method do you believe would be the least effective? Do the opt-in and opt-out policies reach out to all pregnant women?
Table. Percentage of Pragnant Women Who Get Tested, by State of Residence, 1998-1999
|
State
|
Testing Approach
|
% of Pregnant Women Getting HIV Tests
|
|
Tennessee
|
Opt-out
|
85
|
|
New York
|
Mandatory newborn testing
|
83
|
|
Connecticut
|
Mandatory newborn testing
|
81
|
|
Maryland
|
Opt-in
|
69
|
|
Georgia
|
Opt-in
|
66
|
|
Minnesota
|
Opt-in
|
62
|
|
California
|
Opt-in
|
39
|
|
Oregon
|
Opt-in
|
25
|
3. Interpret the data shown in Table below in terms of how effective the testing approaches are.
4. Why do you think the opt-out policies are most effective?
5. Because of the results shown in Table 1, the CDC recommends that states that have an optin policy and a low percentage of pregnant women who get tested for HIV should reevaluate their current policy and ideally change it to be opt-out. What are some reasons why states and their citizens would not want to adopt an opt-out policy?
Part II
6. Define the following terms:
A. Sensitivity:
B. Specificity:
C. Positive Predictive Value:
D. Negative Predictive Value:
7. A new low-cost diagnostic test, is developed to screen for HIV in mothers. The performance of new test in actual trials is presented in the table below.
|
|
HIV+
|
HIV-
|
|
Tests Positive
|
63
|
39
|
|
Tests Negative
|
9
|
136
|
Calculate and interpret the following:
A. Sensitivity
B. Specificity:
C. Positive Predictive Value:
D. Negative Predictive Value:
8. How many false positives are there? Why is this number a concern?
9. How many false negatives are there? Why is this number a concern?
10. Overall, do you think this would make a good screening test? Why or why not?