MONTREAL — Women who smoke cigarettes appear to be more likely than others to become infected with the AIDS virus, according to a study of Haitian women that found that smokers were nearly twice as likely as nonsmokers to be infected with the human immunodeficiency virus (HIV).
The researchers, speaking here Tuesday, said cigarette smoking may simply go along with certain sexual practices that put women at risk of infection. Or, they said, the apparent link between smoking and infection may be attributable to "the biological effects of smoking."
"I would be reluctant to extrapolate our data to any other population groups at this time," cautioned Dr. Neal Halsey of Johns Hopkins University, who presented the results of his study of more than 4,000 women at the Fifth International Conference on AIDS.
Some researchers previously have linked cigarette smoking to cervical diseases, including cancer, and have found byproducts of smoke in cervical fluid. Studies have also turned up evidence that smoking may affect the immune and endocrine systems.
But experts advised caution in interpreting Halsey's results.
Dr. King Holmes, a professor of medicine at the University of Washington who has explored links between smoking and other sexually transmitted diseases, warned that "biological plausibility is only one of the tests one uses in trying to assess these associations."
Holmes said the apparent association must be studied further to see whether it surfaces in other scientifically rigorous research. He said researchers might look for a dose-effect relationship--that is, does the risk of infection rise in proportion to how many cigarettes a person smokes?
Halsey's team tested the blood of low-income women living in an urban slum north of Port-au-Prince. Nearly 10% of the women, whom Halsey described as poor and mostly illiterate, turned out to be infected with the AIDS virus.
But 8.8% of those who were infected turned out to be smokers. Of the uninfected, only 4.6% were smokers.
Of those who smoked more than four cigarettes a day, 25.6% were infected. Among the nonsmokers, only 9.2% were infected.
Halsey acknowledged that there were potentially significant differences between the two groups, which consisted respectively of 207 smokers and 3,962 nonsmokers.
The smokers were less likely to be married and more likely to have had more than one sexual partner, Halsey said. There was no difference in education level or home ownership, but the smokers were very slightly more likely to have tested positive for syphilis.
When the researchers attempted to control those differences by using statistical calculations, Halsey said they found that "even after adjusting for the sexual practices . . . smoking retained an independent association" with HIV infection.
To further explore the possibility that the smokers' behavior might account for the link between infection and smoking, Halsey's team enlisted the help of a cultural anthropologist to find an effective way of obtaining detailed sexual histories of the women.
The researchers then went back and interviewed 101 of the smokers and 253 nonsmokers. They learned that the smokers had had their first sexual experiences earlier and were more likely to have had unprotected sex. They were also more likely to have had oral ulcers and to have consummated oral sex.
"Therefore, it is clear that there are some additional risk behaviors that . . . we may not have taken into account," Halsey said. "But is it also possible that there might be a biologic effect between smoking and risk of HIV transmission by heterosexual contact?"
Halsey cited "a number of physiologic changes associated with smoking that we think might possibly play a role." As examples, he pointed to changes in the immune system and in the tissue in the female genital tract, and what he described as a possible role of smoking as a so-called co-factor in promoting cervical cancer.
Also at the conference Tuesday, researchers reported preliminary results from the first so-called needle-exchange program in the United States--one of several controversial attempts to slow the spread of AIDS among intravenous drug users by giving drug users sterile needles and syringes in exchange for used and contaminated equipment.
The program, begun last August in Tacoma, Wash., appears to have helped cut down on needle-sharing, the practice whereby addicts spread HIV infection. At the same time, it appears not to have contributed to any increase in drug use by participants, as had been feared, the researchers said.
"There is a clear, significant and substantial reduction in HIV transmission behavior, but it is clearly not an elimination of HIV transmission risk," said Don C. Des Jarlais, a New York State drug-abuse expert who reported the findings.