Factors associated with a reduced risk of pneumonia after adjustment for confounders in the HIV-positive subgroup included body mass index (BMI; HIV-positive: OR 0.85 [95% CI 0.75–0.95, p=0.008]), increasing CD4 count (OR 0.99 [95% CI 0.99–0.99, p<0.001]) and antiretroviral therapy (OR 0.23 [95% CI 0.09–0.60, p=0.002]). This evidence concerns the gene CD4 and pneumonia.