CHICAGO - Public health officials are working to reduce mother-to-child HIV transmission, but their efforts are meeting with mixed results. While perinatal HIV transmission has greatly decreased in developed countries, major challenges remain in developing countries.
"We are on the verge of virtual elimination of perinatal HIV transmission in resource-rich settings," said Mary Glenn Fowler, MD, chief of Maternal Child Transmission, Pediatric and Adolescent Studies section at the Centers for Disease Control and Prevention. "The means are remarkably clear: Identify HIV-infected women, either before or during pregnancy; offer highly active antiretroviral therapy (HAART) appropriate for the woman's health care as well as zidovudine (AZT, Retrovir, GlaxoSmithKline) prophylaxis and cesarean section; achieve non-detectable viral load at delivery; avoid breast-feeding, and the risk of transmission is probably 1% or less."
Transmission rates in the United States and Europe have dropped from between 19% and 21% a few years ago to between 2% and 3% in 2000. Zidovudine and HAART have contributed greatly to these reductions. Approximately 78% of pregnant women are now treated with combination therapy, and 42% also receive a protease inhibitor as part of their treatment.
Elective cesarean sections among women with HIV have also contributed to the decline. While only 20% of U.S. women with HIV delivered by cesarean section in 1998, between 40% and 45% delivered this way in 2000. In Europe, 77% to 80% of all women with HIV deliver by cesarean section.
Despite these improvements, many women remain at risk in the United States.
"These include late-presenting women who may not have received prenatal care, and therefore, were not tested," said Fowler, who spoke here at the 8th Conference on Retroviruses and Opportunistic Infections. "There are also, particularly in the private sector, women who did go for prenatal care but were not offered testing, generally because they were perceived to be at low risk." Additionally, some women may not have adhered to prescribed therapy, and others may deliver an infected infant despite adhering to therapy.
Researchers are investigating the feasibility of offering voluntary rapid counseling and testing at delivery to late presenters whose status is unknown. Additionally, Congress is allocating $10 million per year for the next three years to states with high prevalence of perinatal AIDS cases to improve antenatal counseling and testing services, and treatment services for HIV-positive pregnant women. Other studies are examining the effects of using combination therapy in pregnant women, according to Fowler.
In contrast to the U.S. situation, preventing vertical HIV transmission presents much bigger challenges in developing countries. "The obstacles to mother-to-child transmission prevention in most of the world remain daunting," Fowler said.
One challenge is the sharp increase in seroprevalence among adolescent girls. High seroprevalence among all populations in eastern and southern Africa is also a major problem.
Fowler noted that in some communities in western Kenya, for example, seroprevalence among 15-year-old girls is 8%. By age 17, it is close to 30%. Among boys, such increases are seen by age 19.
Breast-feeding may also be a risk factor for HIV, but one that is difficult to avoid. "Breast-feeding transmission is creating major dilemmas and decisions for women in resource-poor settings where breast-feeding in general is very lifesaving for their infants," Fowler said.
Researchers have identified a number of risk factors for HIV transmission through breast-feeding over the last several years. Fowler cited one study suggesting that younger maternal age and duration of breast-feeding may play a role. Additionally, seroconversion during the postpartum period may increase risk. One study noted a sixfold increase in transmission risk due to seroconversion in the postnatal period. Other studies have shown that nipple lesions, bleeding nipples, breast-feeding for longer than 15 months and infant thrush at younger than 6 months may contribute to increased risk of mother-to-child HIV transmission as well.
Precisely defining HIV transmission risk for breast-fed infants is difficult. One study estimated that the risk of mother-to-child HIV transmission is 0.6% to 0.7% between age 1 month and 1 year and 0.2% to 0.3% between age 1 year and 2 years. However, other studies in Nairobi and western Africa put the risk at 9% to 12% during the entire breast-feeding period. Another study showed that one-third of mother-to-child HIV transmission occurs during the breast-feeding period (up to age 2), and half of that occurs within the first six months of life.
Twelve trials are investigating the effects of breast-feeding on mother-to-child HIV transmission, according to Fowler.
Lack of resources in developing countries also makes reducing vertical HIV transmission difficult. "For governments and public health communities, competing health priorities in the face of scarce resources make prioritization of maternal-to-child prevention of HIV one of many competing issues," Fowler said. "Although antenatal care services are certainly available, the use of voluntary counseling and testing and the infrastructure for that are fairly lacking in the majority of settings. For women who may decide that they do not want to be tested, a number of factors may come into play. Fear, stigma and the lack of treatment may mean for many women that they won't go ahead and have counseling and testing in the antenatal period."
While it has been complicated to reduce mother-to-child HIV transmission in Africa, pilot programs in Thailand are showing that these reductions can be accomplished.
For more information:
- Fowler MG. Update on prevention of mother-to-child HIV transmission: U.S. successes, international challenges. Session 36. Paper 16. Presented at the 8th Conference on Retroviruses and Opportunistic Infections. Feb. 4-8, 2001. Chicago.
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