A study tracking 2000 infants in Zimbabwe showed that mothers who are HIV-positive are less likely to transmit AIDS to their babies if they breast-feed exclusively rather than combining breast-feeding with a diet of animal milk and solids. Researchers gathered data on the babies'diets and the rate of AIDS infection from birth until age 2. They found that those babies who were fed only breast milk were 3 times less likely to die. They also found that not introducing solids until around 3 months would contribute to a lower incidence of AIDS infection. Johns Hopkins University Associate Professor Jean Humphrey said that these findings were significant because many African mothers are not able to find a safe, reliable milk substitute for their babies.