area with 2% HIV infection, the positive predictive value of the ELISA would increase to 95% (see Appendix K).

To maximize prevention efforts, women must be identified as HIV-infected as early as possible during pregnancy. Early diagnosis of HIV infection allows the mother to avail herself of effective antiretroviral therapy for her own health, and that can significantly reduce perinatal transmission. Women who know their HIV status can be counseled not to breast-feed their infants. HIV-infected pregnant women can also be referred to appropriate psychological, social, legal, and substance abuse services.

Reporting of conventional ELISA and Western blot tests typically takes one to two weeks. At present, one rapid test (Single Use Diagnostic System HIV Test, Murex Corporation, Norcross, Georgia) is commercially available in the United States. As discussed in Chapter 7, an accurate rapid test would have utility among pregnant women in labor who do not know their HIV status. It would help identify HIV-infected pregnant women whose infants might still benefit from the intrapartum and postpartum components of the ACTG 076 regimen. Rapid tests can also be performed on newborns to ascertain their HIV exposure. The sensitivity and specificity of current rapid assays are comparable to those of ELISAs. Because the predictive value varies with the prevalence of HIV infection in the population tested, the positive predictive value of the test will be low in populations with low-prevalence, yielding many false positive results. A reactive rapid test must therefore be confirmed by standard testing. If a second rapid test is licensed, its performance would be independent of the current test, and the sensitivity and specificity of the pair would be sufficient for use in perinatal settings (CDC, 1998g). See Chapter 7 for further discussion.

Early diagnosis of HIV-infected infants is crucial for optimal medical management. Serologic methods are of limited utility for the early diagnosis of perinatal HIV infection. With efficient transfer of antibodies from an infected woman to her fetus during the third trimester of pregnancy, all infants born at or near term to an HIV-infected woman will be HIV-seropositive; uninfected infants may retain passively acquired antibodies through 18 months of age.

The detection of HIV proviral genome in peripheral blood mononuclear cells using the polymerase chain reaction (DNA PCR) is a highly sensitive, specific, rapid, and cost-effective screening test for vertical infection (Bremer et al., 1996; Luzuriaga et al., 1996). Using DNA PCR, 25% to 30% of infected infants may be identified at birth and the remaining 70% to 75% of infected infants can be identified by one month of age. According to the guidelines, the evaluation of the infants' infection status should begin within 48 hours of birth, with repeated evaluations at one to two weeks and at one, two, and six months (CDC, 1998c). Infants with single positive DNA PCR results should have a follow-up blood specimen drawn immediately for confirmatory studies (DNA PCR and viral isolation). The likelihood of infection is extremely low in those infants with negative DNA PCR studies through 6 months of age; subsequent serologic follow-up



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