In the developed world, medical interventions allow HIV positive women to safely give birth with low risk of infecting their babies. Tactics to prevent mother-to-child transmission of HIV include taking antiretroviral drugs during pregnancy, cesarean sections to prevent blood mixing between the mother and baby, and feeding formula instead of breast milk. Unfortunately, in resource-poor countries such as in sub-Saharan Africa, many of these interventions are hard to come by. Transmission of HIV through breast milk is especially common, as breast feeding until children are a few years old is traditional in many African communities. Studies estimate that if a child is breastfed until 18 months, the risk of transmission from an HIV positive mother is nearly 10 percent.
Not every HIV positive mother is equally likely to transmit the disease to her children. Risk factors such as the amount of virus present in the mother’s blood, or viral load, and her CD4+ T cell counts both influence the likelihood of transmission. To study the epidemiology of these risk factors in HIV transmission via breastfeeding in older infants, VIDI associate member Dr. Ying Chen and colleagues looked at viral load and CD4+ T cell levels of HIV positive mothers in an HIV Prevention Trials Network clinical trial aiming to prevent mother-to-child transmission.
Chen and colleagues assessed how reducing viral loads and raising CD4+ T cell counts in sub-Saharan African mothers with advanced HIV disease would impact the overall HIV transmission through breastfeeding. The researchers found that 16 percent of the mothers in this trial had low CD4+ T cell counts (<200 cell/mm3), 25 percent had high viral load (>50,000 viruses/ml), and 8 percent had both low CD4+ counts and high viral loads. The researchers further calculated that if these levels were ameliorated with proper antiretroviral therapy, the overall mother-to-child transmission rates in the population would drop by 26, 37 and 16 percent, respectively. These drastic reductions of transmission indicate that scaling up the use of antiretroviral therapy is especially important for reducing overall mother-to-child transmissions from this group of breastfeeding HIV positive mothers.
Population Attributable Fractions for Late Postnatal Mother-to-Child Transmission of HIV-1 in Sub-Saharan Africa. Chen YQ, Young A, Brown ER, Chasela CS, Fiscus SA, Hoffman IF, Valentine M, Emel L, Taha TE, Goldenberg RL, Read JS. J Acquir Immune Defic Syndr. 2010 Mar 10.