I am a foster care provider and have been approached to take a 10 month old baby that has been born to an HIV+ mother. This child has been tested twice and both time been negative for HIV. Is there a chance that this child will develop the virus later? If so what are the chances?

All HIV positive women make antibodies (a type of immune response) to the virus and pass the antibodies to their babies. However, only about 25-30% of women with HIV infection will pass the virus to their babies; if a mother takes antiviral medications, the risk of transmitting the virus is even lower.

Because mothers pass antibodies to their babies and it takes up to 18 months for the babies to clear the antibodies, we can not use routine antibody testing to diagnose infection in babies. The preferred method is "PCR" in which we look for viral nucleic acids (RNA or DNA) in the babies' blood. This test is positive in the majority of infected babies by 1-2 months of age.

You don't mention what type of testing was done or when the testing was done. If PCR testing was done on your baby and your baby had 2 or more negative tests after 2 months of age, your baby would be considered uninfected.