Smoking increases risk of HIV acquisition, but no link with faster progression to AIDS

Smoking is an independent risk factor for HIV infection, according to investigators from Sheffield, writing in the February edition of Sexually Transmitted Infections. The researchers conducted a meta-analysis of studies exploring this issue. However, an analysis of studies looking at the link between smoking and progression to AIDS failed to find any link.

There is a growing recognition that smoking can increase the risk of infections. It is thought that this is due to immunological changes caused by smoking, including depression of antibody responses, lowered CD4 cell count, increased CD8 cell count, and decreased release of cytokines. However, it is unclear how these immunological changes relate to clinical outcomes. Investigators therefore conducted a systematic review of studies, published in journals and presented to recent international AIDS conferences to see if smoking was associated with an increased risk of HIV seroconversion or progression to AIDS.

To be included in the investigators’ analysis the studies had to include adults exposed to HIV and to consider smoking as a risk factor for HIV acquisition or progression to AIDS. A total of 15 studies met these criteria, with nine of the studies looking at progression to AIDS, five examining HIV seroconversion, and one examining both.

Five of the six papers looking at smoking and the risk of acquiring HIV infection found that smoking tobacco was an independent risk factor. In these studies smokers had an adjusted odds ratio of between 1.6 to 3.5 of infection with HIV, “a magnitude of public health significance”, according to the investigators.

A total of ten papers looked at the link between smoking and progression to AIDS. Nine of these papers found no such link. The single study that did find a link was described by the investigators as being of “poorer quality.” Two studies did, however find a link between smoking and bacterial pneumonia, and one of these also found that smokers had an increased risk of developing AIDS-related dementia, but it also found that smoking was protective against the AIDS-defining cancer, Kaposi’s sarcoma.

“The studies identified in this systematic review indicate that while smoking might be independently associated with acquiring HIV, it does not appear to be related to progression to AIDS”, write the investigators. They add, “the consistency of the findings is striking and represents a major strength of this review.”

But the investigators’ analysis highlighted a need for more research into these issues. They write, “further research is needed to investigate whether the association between smoking and HIV seroconversion is related to residual confounding.” Additional research is also needed to see if smoking is causing “intercurrent illness, which could contribute to general debilitation and progression to AIDS”, such as bacterial pneumonia and tuberculosis in resource-limited countries. Furthermore, research is needed to see if there is a link between smoking and lipid abnormalities and cardiovascular disease in patients taking antiretrovirals.

“The public health message on smoking remains clear - tobacco is not good for health”, conclude the investigators. However, they acknowledge that stopping smoking may not be a priority for many HIV-positive individuals - some of the groups most at risk of HIV, particularly gay men and sex workers, have high rates of smoking and in many countries these groups are marginalised and it is difficult to offer any sort of support, “let alone smoking cessation services.”