Studies have consistently shown that of infants born to HIV-infected mothers, only the 15-40 percent of infants who become HIV-infected before or during birth go on to develop immunosuppression and AIDS, while babies who are not HIV-infected do not develop AIDS (Katz, 1989; d'Arminio et al., 1990; Prober and Gershon, 1991; European Collaborative Study, 1991; Lambert et al., 1990; Lindgren et al. 1991; Andiman et al., 1990; Johnson et al., 1989; Rogers et al., 1989; Hutto et al., 1991). Moreover, in those infants who do acquire HIV and develop AIDS, the rate of disease progression varies directly with the severity of the disease in the mother at the time of delivery (European Collaborative Study, 1992; Blanche et al., 1994).

Almost all infants born to seropositive mothers have detectable HIV antibody, which may persist for as long as 15 months. In most cases, the presence of this antibody does not represent actual infection with HIV, but is antibody from the HIV-infected mother that diffuses across the placenta. In a French study of 22 infants born to HIV-infected mothers, seven babies had antibodies to HIV after one year and all developed AIDS. In these seven infants, the presence of HIV antibodies marked actual infection with HIV, not merely antibodies acquired from the mother. The other 15 children showed a complete loss of maternally acquired HIV antibodies, were not actually infected, and remained healthy. Of the babies who developed AIDS, virus was found in four of four infants tested. HIV was not found in the 15 children who remained healthy (Douard et al., 1989; Gallo, 1991).

In the European Collaborative Study, children born to HIV-seropositive mothers are followed from birth in 10 European centers. A majority of the mothers have a history of injection drug use. A recent report showed that none of the 343 children who had lost maternally transferred HIV antibodies (i.e. they were truly HIV-negative) had developed AIDS or persistent immune deficiency. In contrast, among 64 children who were truly HIV-infected (i.e. they remained HIV antibody positive), 30 percent presented with AIDS within 6 months of age or with oral candidiasis followed rapidly by the onset of AIDS. By their first birthday, 17 percent died of HIV-related diseases (European Collaborative Study, 1991).

In a multicenter study in Bangkok, Thailand, 105 children born to HIV-infected mothers were recently evaluated at 6 months of age (Chearskul et al., 1994). Of 27 infants determined to be HIV-infected by polymerase chain reaction, 24 developed HIV-related symptoms, including six who developed CDC-defined AIDS and four who died with conditions clinically consistent with AIDS. Among 77 exposed but uninfected infants, no deaths occurred.

In a study of 481 infants in Haiti, the survival rate at 18 months was 41 percent for HIV-infected infants, 84 percent among uninfected infants born to seropositive women, and 95 percent among infants born to seronegative women (Boulos et al., 1994).

Investigators have also reported cases of HIV-infected mothers with twins discordant for HIV-infection in which the HIV-infected child developed AIDS, while the other child remained clinically and immunologically normal (Park et al., 1987; Menez-Bautista et al., 1986; Thomas et al., 1990; Young et al., 1990; Barlow and Mok, 1993; Guerrero Vazquez et al., 1993).