The New York Times

Thursday, February 3, 2000

A New AIDS Mystery: Prostitutes Who Have Remained Immune

By LAWRENCE K. ALTMAN

SAN FRANCISCO, Feb. 2 -- One of the mysteries of the AIDS epidemic is that a small number of female prostitutes in Africa seem resistant to the virus that causes the disease even though they often have sex with infected men.

Despite an intensive search for immunologic explanations, none have been found.

Now an even more baffling finding has turned up in a study of 1,900 prostitutes in Nairobi, Kenya. Four of them became infected with H.I.V., the virus that causes AIDS, but only after they stopped working as prostitutes or took breaks of two months or more, leaders of the study reported at the Seventh Conference on Retroviruses and Opportunistic Infections, which ended here today.

Scientists cannot explain this seeming paradox but say the answer could affect development of an AIDS vaccine.

The prostitutes work in a Nairobi slum. In 1984, researchers from the University of Nairobi and the University of Manitoba in Winnipeg, Canada, began to study and treat the women's sexually transmitted diseases.

When the women enrolled in the study, two-thirds of them were infected with H.I.V. The prostitutes said they had five clients a day on average and used condoms with about four of them. The researchers estimated that each prostitute had unprotected sex with 60 to 70 infected clients a year.

A small percentage of the prostitutes remained free of infection for at least three years. No link has been found between the women who became infected after stopping commercial sex and their condom use or sex practices.

Dr. Stephen Wolinsky, an AIDS researcher at Northwestern University, called the findings provocative and said he had confidence in them because they came from a scientific team known for meticulous work.

Scientists have been stymied in identifying what immunologic factor specifically correlates with protection against H.I.V. infection. Findings from the Nairobi study may provide another way of seeking the factors that are known as correlates of immunity, Dr. Wolinsky said in an interview at the meeting.

Such information is needed to help create a vaccine. But the findings could be bad news for vaccine development if they meant that booster doses would be needed every few weeks to maintain protection, Dr. Anthony S. Fauci, who directs the National Institute of Allergy and Infectious Diseases, said in an interview at the meeting.

Dr. Fauci offered two possible explanations for the phenomenon.

It could be, he said, that to maintain protection, people need nearly continual exposure to H.I.V. so that antigens in the virus can constantly boost the immune system.

Or, he said, perhaps sperm or semen somehow stimulate a relatively short-lived immunologic reaction in the women that protects them.

If either explanation is correct, an effective H.I.V. vaccine may need to be given frequently, Dr. Fauci said.