Breastfeeding, which helps build a baby's immune system, may be the best option for HIV-infected mothers in developing countries, despite the risk of transmitting the virus that causes AIDS to their babies, according to new studies presented at the 14th Conference on Retroviruses and Opportunistic Infections. HIV-positive mothers generally are counseled to feed their babies formula to limit the risk of transmission of the human immunodeficiency virus, but that has caused problems in nations where clean water and other needs may not be met.