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September 25, 2006
Smokers May Be at Greater Risk of HIV Infection
by Tim Horn
September 25, 2006 (AIDSmeds)—Smokers may be at greater risk of HIV infection than nonsmokers, according to an in depth analysis of several studies published over the past 16 years. The evaluation of the studies, to be published in a forthcoming issue of Sexually Transmitted Infections, also suggests that cigarette smoking is not associated with more rapid disease progression in HIV-positive people. However, this may be a premature finding, in light of data involving HIV-positive smokers that was not available at the time of this systematic review.
According to Andrew Furber, MD, of the South East Sheffield Primary Care Trust in Sheffield, England, and his colleagues, cigarette smoking has already been linked to an increased risk of contracting various infections, including those that can be transmitted sexually. They point out that cigarette smoking is associated with immunological changes – including altered antibody and cellular responses – that can allow disease-causing microorganisms to establish themselves in the body. Human papillomavirus (HPV), for example, is more likely to cause pre-cancerous cervical and anal lesions in HIV-positive and HIV-negative smokers compared to non-smokers.
In February 2005, Dr. Furber’s group evaluated the published results of several studies exploring connections between cigarette smoking and HIV infection and/or disease progression in HIV-positive people.
Six studies reviewed by Dr. Furber's team assessed the association between cigarette smoking and becoming HIV positive. Five of the studies, published between 1990 and 1996, concluded that smokers were two to three times more likely to become infected with HIV compared to non-smokers.
The authors noted that it was difficult to draw firm conclusions from these studies, given that they were all conducted differently and had important limitations. For example, the six studies relied solely on self-reports of smoking and did not conduct blood tests to confirm the absence of nicotine in participants who denied cigarette use. This, in turn, may have led to inaccurate comparisons between smokers and “non-smokers.” However, given the established risks between cigarette smoking and other infections, along with the relatively consistent findings of the studies, Dr. Furber’s group concluded that there is likely an increased risk of HIV infection among smokers.
Ten additional papers looked at the association between smoking and progression to AIDS in people with HIV infection. Nine of the studies, however, found that HIV-positive smokers were not at increased risk. The one study that did find an associated was considered to be scientifically weak and incapable of yielding firm conclusions.
It is important to note, however, that the analysis by Dr. Furber's group did not include the results of an important study published in May 2006. The study, involving 924 women enrolled in the ongoing Women’s Interagency HIV Study (WIHS), demonstrated that HIV-positive women who smoke while on HIV treatment have a 36% increased risk of getting an AIDS-related disease compared to their non-smoking peers. While the risk of AIDS-related death was no different between the two groups, the smokers were 53% more likely to die overall.
A simple take-home message offered by Dr. Furber’s group involves the need to encourage people to give up smoking as an essential public health measure. However, the authors stressed that additional studies are needed to evaluate the potential connection – including the biological mechanisms involved – between cigarette smoking, HIV infection, and HIV disease progression.