SHEFFIELD, England -- Smoking cigarettes seems to be an independent risk factor for HIV infection, according to researchers here. But smoking doesn't appear to be a risk factor in progression to AIDS.
SHEFFIELD, England, Sept. 21 -- Smoking cigarettes seems to be an independent risk factor for HIV infection, according to researchers here.
On the other hand, found a meta-analysis, smoking doesn't appear to be a risk factor in progression to AIDS, said Andrew Furber, M.D., of the South East Sheffield Primary Care Trust here.
Because tobacco and HIV/AIDS are the two major health threats that continue to expand, "the intersection of these two epidemics represents an area of growing clinical and public health importance" Dr. Furber and colleagues reported in the online issue of Sexually Transmitted Diseases.
Evidence is mounting that cigarette smoking in creases the risk of infection, including sexually transmitted diseases, the researchers said, but it had not been known whether smoking has an effect on either HIV seroconversion or progression to AIDS.
In a literature review, the researchers identified 15 studies that dealt with the question. Five of the studies used seroconversion as an outcome measure, nine used progression to AIDS, and one used both. Few of the studies verified smoking status biochemically.
Of the six papers dealing with HIV seroconversion, Dr. Furber and colleagues found, all but one found a significant association, with adjusted odds ratios ranging from 1.6 to 3.5. The other paper found an odds ratio of 1.22, but the 95% confidence interval was 0.99 to 1.50 and was consistent with no association.
Of the 10 papers that dealt with progression to AIDS, one found an association and nine did not, the researcher said.
"The consistency of the findings is striking and represents a major strength of this review," Dr. Furber and colleagues said, noting that while the studies vary, many had large sample sizes and were of high quality.
On the other hand, the researchers said, the methodologies used -- epidemiological and observational -- can't make causal connections and are "prone to confounding."
All but one of the seroconversion studies were cross-sectional and the single prospective study found no association, they said, while all of the AIDS studies were cohort studies and eight of 10 were prospective. None was randomized.
Confounding is more likely in cross-sectional studies, which may explain the apparent paradox that smoking is associated with seroconversion but not progression to AIDS, Dr. Furber and colleagues said.
On the other hand, there are theoretical grounds for expecting the smoking could increase the risk of HIV infection and the odds ratios found suggest some public health importance.
At the same time, most of the AIDS studies evaluated were done before the widespread use of antiretroviral therapy and it may be that -- when the disease course is short -- smoking contributes little to the risk of progression, the researchers said.
Most of the studies in the review were set in developed countries, but the brunt of both epidemics -- smoking and HIV -- is being felt in the developing world, Dr. Furber and colleagues said.
"The public health message on smoking remains clear -- tobacco is not good for health," the researchers concluded.