Page 32 - AIDSBK23C

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mortality, even extending into the second year of life. Intensive maternal nutritional and
counseling interventions reduce but do not appear to eliminate this excess mortality.[182]
Features of HIV-1 that appear to correlate with perinatal transmission include: rapid or
high-titer replication in maternal human peripheral blood mononuclear cells, T-cell tropism, and
resistance to neutralization or a sensitivity to enhancement of infection by maternal serum.[180]
Measurement of maternal HIV-1 RNA can predict perinatal transmission risk. High levels of
HIV-1 RNA late in gestation and/or during labor and delivery increase the risk for perinatal
transmission.[183] The frequency of perinatal HIV-1 transmission in the first and second
trimesters is low.[184] Half of infections occur during the intrapartum period.[179]
Though HIV-1 transmission from mother to fetus may still occur over a wide range of
plasma HIV-1 RNA levels and of CD4 lymphocyte counts, antiretroviral therapy that reduces the
HIV-1 RNA level to below 500 copies/mL appears to minimize the risk of perinatal transmission
as well as improve the health of the mother. Thus, the maternal HIV-1 RNA level can predict
the risk, but not the timing, of HIV transmission to their infants.[185,186]
To date, most reported perinatal HIV-1 cases in the United States have been a
consequence of injection drug use by mothers, but an increasing proportion of cases is appearing
from heterosexually acquired HIV by mothers.[179] Congenital AIDS is most common in
populations where heterosexual HIV transmission and the frequency of women infected with
HIV is higher. In contrast, perinatal transmission of HIV-2 occurs far less frequently, with a rate
of only 1 to 2%.[187]