In resource-limited settings, HIV-infected mothers of HIV-uninfected infants often confront a difficult dilemma with regard to infant feeding: breastfeeding risks transmitting HIV to their infants, but formula feeding may not be a viable option due to high cost, lack of clean water, or stigma associated with not breastfeeding. Fortunately, recent clinical studies have established that HIV-infected mothers can breastfeed with minimal risk of HIV transmission to their infants, as long as the mother and the infant receive appropriate antiretroviral prophylaxis.
Epidemiology of HIV Acquisition from Breastfeeding
In the absence of any antiretroviral prophylaxis for either the mother or the infant, the risk of HIV transmission from mother to infant is 30 to 45% for breastfeeding infants and 15 to 30% for infants who are not breastfed (Figure 1). Globally, up to 40% of HIV infections in infants have resulted from breastfeeding. The risk of HIV transmission is highest in the first few months of breastfeeding[3,4,5], but risk continues throughout the breastfeeding period; infants who are breastfed the longest have the highest risk of acquiring HIV[6,7]. Both maternal factors (high HIV viral load, mastitis, or maternal illness) and infant factors, such as oral candidiasis, can increase the infant's risk of acquiring HIV from breastfeeding[1,8].
Mortality and Morbidity in Non-breastfed Infants in Resource-limited Settings
Formula feeding, as a replacement for breastfeeding, reduces the risk of HIV transmission to infants of HIV-infected mothers, but it is associated with high morbidity and mortality rates in resource-limited settings[9,10,11,12,13,14]. The increased mortality associated with formula feeding in these settings is likely due to the absence of key breast milk-associated antibodies that provide protection against infectious diseases. In addition, the water used for formula preparation may be contaminated, resulting in severe gastrointestinal infections. Furthermore, infant formula may not be affordable, and formula feeding in some settings may carry a social stigma and imply that the mother is infected with HIV. For these reasons, the WHO guidelines endorse formula feeding over breastfeeding only in situations where six specific conditions are met (Figure 2).
Extended Daily Infant Nevirapine to Prevent HIV Transmission via Breastfeeding
Although single-dose nevirapine given to the infant is effective in preventing peripartum and early breastmilk transmission of HIV, its effect does not extend beyond the first few weeks of life. Several studies have evaluated longer-term daily nevirapine prophylaxis given to the infant, and all show that extended nevirapine prophylaxis for breastfeeding infants is more effective than single-dose nevirapine in reducing both HIV infection and infant mortality, particularly for those infants whose mothers are not receiving antiretroviral therapy. Extended infant nevirapine has been studied for 6 weeks (Figure 3), 14 weeks (Figure 4Study Title and SourceInfection During 1st YearsDeath During 1st YearsInfection or Death), and 6 months (Figure 5Study Title and SourceProbability of InfectionProbability of Infection or Death); the benefit to the infants continued for as long as nevirapine was given. Extended zidovudine, alone or in combination with nevirapine, is also effective at reducing HIV transmission, but has been associated with high rates of infant anemia and neutropenia[11,18]. For breastfeeding infants of HIV-infected mothers not receiving a triple antiretroviral drug regimen, the WHO therefore recommends the use of daily nevirapine from birth and until 1 week after all exposure to breast milk has ended (or for a minimum of 4 to 6 weeks if breastfeeding ceases prior to 6 weeks). Antiretroviral prophylaxis recommendations for infants of mothers receiving a triple-drug antiretroviral regimen are discussed below.
Maternal Antiretroviral Drugs to Prevent HIV Transmission via Breastfeeding
Multiple studies have established that administration of a triple-drug antiretroviral regimen to HIV-infected pregnant women who breastfeed reduces the risk of HIV transmission to their infants[19,21,22,23,24,25,26]. This finding applies to women who meet antiretroviral therapy eligibility criteria based on low CD4 count and/or advanced HIV disease, as well as to women with less advanced HIV disease who do not meet antiretroviral therapy eligibility criteria. The success of this approach derives from the effectiveness of triple-drug antiretroviral regimen in reducing maternal serum and breast milk HIV viral load, the strongest determinants of HIV transmission via breast milk. Rates of transmission are lowest when women initiate drugs early in pregnancy, underscoring the importance of promoting early antenatal care and prompt HIV diagnosis and management during pregnancy. The most impressive results were seen in the Mma Bana ("mother of the baby") study (Figure 6), where prophylaxis began as early as the second trimester and the overall rate of HIV transmission was 1.1%. The HIV transmission rates in most other studies of triple-drug antiretroviral prophylaxis, where antenatal prophylaxis was not initiated until mid-to-late third trimester, have ranged from 5 to 8% (Figure 7). If the HIV-infected mother is breastfeeding and receiving a triple-drug antiretroviral regimen only for prophylaxis (e.g., she doesn't require treatment for her own health) and plans to stop the regimen after breastfeeding cessation, she should continue the antiretroviral drugs until 1 week after all infant exposure to breastmilk has ended.
Antiretroviral Prophylaxis for Infants of Mothers Receiving Triple-Drug Regimens
Administration of daily nevirapine or twice-daily zidovudine to the infant is recommended for the first 4 to 6 weeks of life, even if the mother is receiving a triple-drug antiretroviral regimen for treatment or prophylaxis. Infant antiretroviral prophylaxis is particularly important in infants of mothers who either received no antepartum antiretroviral drugs or started drugs late in pregnancy: nevirapine or zidovudine given directly to the infant provides prophylaxis against HIV that might persist in the mother's breast milk due to insufficient maternal exposure to antiretroviral drugs prior to delivery. Continuing the infant prophylaxis beyond 6 weeks when the mother is receiving a triple-drug antiretroviral regimen does not appear to provide any additional benefit.
Importance of Exclusive Breastfeeding
Exclusive breastfeeding, in which the infant receives no supplemental fluids or foods apart from breast milk during the first 6 months of life, is associated with a lower risk of HIV transmission from breast milk when compared with mixed feedings[29,30]. It is hypothesized that mixed feedings disrupt the integrity of the gut endothelium, and facilitate HIV entry via the gastrointestinal tract. Current WHO Guidelines therefore recommend that HIV-infected mothers of infants who are not HIV-infected (or whose HIV status is unknown) should avoid mixed feedings. Mothers should instead exclusively breastfeed for the first 6 months of life, gradually introducing mixed feedings thereafter, while continuing to breastfeed for the first 12 months of life "or until a nutritionally adequate and safe diet without breast milk can be provided".
Importance of Breastfeeding for at Least 1 Year
Previous guidelines endorsed weaning infants from breast milk by 6 months of age in order to reduce the risk of HIV transmission, but clinical studies (Figure 8) and (Figure 9) have subsequently established that, in resource-limited settings, weaning infants at 4 to 6 months of age is associated with marked increases in mortality, hospitalizations, and growth compromise [11,32,33]. The WHO breastfeeding guidelines therefore recommend that after exclusively breastfeeding for 6 months, infants should continue to breastfeed for the first 12 months of life. Since rapid weaning has also been associated with HIV transmission and mastitis, weaning should take place gradually over 1 month. For infants and mothers who are on antiretroviral prophylaxis to prevent HIV transmission, the antiretroviral drugs should continue for 1 week following complete weaning. Mothers who are receiving antiretroviral therapy for maternal health (antiretroviral treatment is indicated) should continue to do so for life.
Use of Heat-treated, Expressed Breast Milk
The WHO has endorsed heat-treated, expressed breast milk as an interim feeding strategy that may enable women to continue breastfeeding under certain conditions. Heat treatment of breast milk inactivates HIV, but does not adversely affect the nutritional quality of breast milk. The use of heat-treated expressed breast milk as a temporary strategy to continue breastfeeding without putting the infant at risk may be considered under certain circumstances, such as low birthweight newborns who cannot breastfeed, women with conditions that may temporarily interrupt breastfeeding (such as mastitis), women whose supply of antiretroviral therapy or prophylaxis is interrupted, or as an adjunct to weaning practices. Under these circumstances, infants should continue nevirapine prophylaxis since they will be consuming breastmilk.
Current WHO Recommendation for Breastfeeding HIV-Infected Mothers
The WHO has issued recommendations for feeding of infants born to HIV-infected mothers and for the use of maternal and infant antiretroviral prophylaxis to prevent HIV transmission from HIV-infected mothers to their infants who are breastfeeding. The key points of these recommendations are summarized as follows:
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