Sixteen prospective cohort or case-control studies evaluated the relationship between cigarette smoking and HIV progression with a variety of endpoints, including CD4 cell counts, time to AIDS, incidence of AIDS, and incidence of opportunistic infections and HIV-related clinical events (). Although sometimes not the primary objective, each of these studies examined whether cigarette smoking was associated with an increased progression of HIV disease among infected individuals.
Cigarette Smoking as a Risk Factor for HIV Progression
Eight studies used CD4 cell counts as the outcome of interest with the objective of determining if cigarette smoking influences CD4 cell count declines. Of these eight studies, only two studies, Royce & Winkelstein (1990) and Feldman et al. (2006)
, identified an association between cigarette smoking and CD4 cell count decline among HIV-infected individuals. Previous studies have concluded that in the absence of HIV infection, cigarette smoking leads to an increase in CD4 cell counts; however this relationship may change when comparing light to moderate to heavy smoking (Arcavi & Benowitz, 2004
). Royce & Winkelstein (1990) found that the positive dose-response relationship between packs smoked per day and CD4 counts observed for HIV-uninfected smokers was substantially decreased in HIV-infected smokers (p<0.01). This study further suggested in a subgroup analysis that CD4 cell counts of cigarette smokers decreased faster than those for non-smokers. In the Women's Interagency HIV Study (WIHS), Feldman et al. (2006)
also confirmed that cigarette smoking leads to increased CD4 counts in HIV-uninfected individuals. Following HIV seroconversion, this study found that the initially higher CD4 cell counts in smokers decreased to below the mean CD4 cell count for nonsmokers over a five-year period, after adjusting for age and race (p=0.01). Among MSM seroconverters, Park et al. (1992)
demonstrated that the somewhat higher CD4 cell counts observed prior to seroconversion among smokers was probably related primarily to an increase in the total white blood cell count and further, that this effect disappeared within three years following seroconversion. In addition to Park et al. (1992)
, the remaining five studies, Burns et al. (1991)
, Craib et al. (1992)
, Conley et al. (1996)
, Miguez-Burbano et al. (2003)
, and Webber et al. (1999)
, all found no relation between cigarette smoking and CD4 cell count decline among HIV-infected individuals.
Eight studies assessed whether cigarette smoking was an independent risk factor for opportunistic infections or HIV-related clinical events. Six of these studies investigated Pneumocystis carinii
pneumonia (PCP) outcomes in HIV-infected individuals. Miguez-Burbano et al. (2003)
found that cigarette smoking was associated with an increased risk for PCP (RR=1.56; p=0.02). In a later publication from these authors (Miguez-Burbano et al., 2005
), they again reported that cigarette smoking was associated with an increased risk of hospitalization due to PCP (OR=2.55, 95% CI 1.27-4.77; p=0.004). Similarly, Nieman et al. (1993)
identified cigarette smoking as an independent risk factor for incident PCP infection (p=0.002). In contrast, Conley et al. (1996)
, Craib et al. (1992)
, and Galai et al. (1997)
found no association between cigarette smoking and PCP.
Two studies evaluated the relationship between smoking and tuberculosis (TB) infection among HIV-positive individuals. Miguez-Burbano et al. (2003)
found that long-term cigarette smokers (20 years or greater) had a three-fold increased risk of incident TB infection when compared to smokers of less than 20 years (p=0.04). However, in a second study, Miguez-Burbano et al. (2005)
did not find a significant association between cigarette smoking and hospitalization due to TB among HIV-infected individuals.
Four studies assessed whether cigarette smoking was an independent risk factor for bacterial pneumonia. Burns et al. (1996)
(HR=1.57, 95% CI 1.14-2.15), Conley et al. (1996)
(RR=2.62, 95% CI 1.30-5.27), and Crothers et al. (2005)
(HR=2.84, 95% CI 1.48-5.45), identified a significant relationship between cigarette smoking and bacterial pneumonia among HIV-positive individuals. Also, Miguez-Burbano et al. (2005)
found that smokers had an increased risk of hospitalization due to bacterial pneumonia compared to nonsmokers (OR=1.80, 95% CI 1.16-2.79; p=0.005).