Drug smoking, Pneumocystis carinii pneumonia, and immunosuppression increase risk of bacterial pneumonia in human immunodeficiency virus-seropositive injection drug users.

To examine the risk factors for the first episode of bacterial pneumonia among human immunodeficiency virus (HIV)-seropositive injection drug users (IDUs), medical record review was performed on IDUs participating in a cohort study from January 1988 to June 30, 1992. HIV-seropositive IDUs with a first episode of bacterial pneumonia (n = 40) were matched with up to five HIV-seropositive control subjects without bacterial pneumonia (n = 197) by date of entry (+/- 3 mo) and length of follow-up. Odds ratios (OR) were estimated using conditional logistic regression. The incidence of bacterial pneumonia was 1.93 in 100 person-years in HIV seropositive and 0.45 in 100 person-years in HIV seronegative subjects (relative incidence = 4.3; 95% CI 2.4 to 7.5). In univariate analyses, CD4 lymphocyte count < 200 cells/microliters previous episode of Pneumocystis carinii pneumonia (PCP), age between 30 and 40 yr and smoking illicit drugs (marijuana, cocaine, or crack) were associated with bacterial pneumonia. Cigarette smoking was associated with an increased odds of bacterial pneumonia (OR = 2.0), but this was not statistically significant because it was nearly universal in this cohort. In multivariate analysis, CD4 < 200 cells/microliters (OR = 6.75, 95% CI 2.13 to 21.42) and smoking illicit drugs (OR = 2.24, 95% CI 1.03 to 4.89) remained significantly associated with bacterial pneumonia. The odds ratio for cigarette smoking in the final model remained at 2.08 but was still not significant (95% CI 0.49 to 8.70). Smoking illicit drugs had the strongest effect on risk of bacterial pneumonia among HIV-seropositive IDUs with a previous history of PCP (OR = 22.94; 95% CI 2.18 to 241.10).