Risk factors for transmission

The process of HIV transmission through breast milk is poorly understood. However, HIV has been detected in breast milk and animal studies suggest that HIV can cross mucosal tissue in the mouth and upper gastrointestinal tract to infect neonates. High viral loads and low CD4 cell counts have been highly associated with transmission, as these may lead to higher viral loads in the breast milk.1 2

Certain factors, including longer breastfeeding and cracked nipples are thought to increase the risk of transmission, although research has not conclusively proven the association. It has been shown, however, that inflammation of the breast or 'mastitis' does increases the risk and that detectable viral load in breast milk is associated with transmission.3 Infection with malaria and low birth weight have also been linked to the risk of HIV transmission during breastfeeding.4

As described above, mixed feeding with breast milk and other foods appears to significantly increase the risk of transmission. However, giving colostrum, the early, antibody-rich secretion from the breast, does not appear to affect the risk of transmission.

Unsurprisingly, both the volume of milk ingested and the length of exposure have been found to be factors in transmission. Ingestion of one litre of breast milk was estimated to pose a comparable risk to that associated with one episode of unprotected vaginal sex with an HIV-positive man.5

References

  1. Pillay K et al. Cell-free virus in breast milk of HIV-1-seropositive women. J Acquir Immune Defic Syndr 24: 330-336, 2000
  2. Rousseau CM et al. Longitudinal analysis of HIV type-1 RNA in breast milk and its relationship to infant infection and maternal disease. J Infect Dis 187: 741-46, 2003
  3. Semba RD et al. Human immunodeficiency virus load in breast milk, mastitis, and mother-to-child transmission of human immunodeficiency virus type 1. J Infect Dis 180: 93-98, 1999
  4. Brahmbhatt HPB et al. Determinants of mother to child transmission of HIV in the uterine/intrapartum period and during breastfeeding in Rakai, Uganda. 14th International AIDS Conference, Barcelona, abstract ThPeC7428, 2002
  5. Richardson B et al. Breastmilk infectivity of HIV-1 infected mothers. Thirteenth International Conference on AIDS, Durban, abstract WeOrC492, 2000
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