Hospitalization for Pneumonia among Individuals With and Without HIV Infection, 1995-2007: A Danish Population-Based, Nationwide Cohort Study

Background. Human immunodeficiency virus (HIV)-infected individuals with high CD4(+) cell counts may have increased susceptibility to other infections. We compared incidence rates of pneumonia among individuals with and without HIV infection and explored risk factors for pneumonia in the HIV-infected population. Methods. This was an observational cohort study conducted during 1995-2007. Each member of a Danish population-based nationwide cohort of HIV-infected individuals was matched with up to 99 control individuals from the general population. Data on age, mortality, emigration, and hospital discharge diagnoses from 1977 onward were obtained from nationwide administrative databases. Individuals without previous hospitalization for pneumonia were observed from the date of HIV diagnosis until the first hospitalization to treat pneumonia (excluding pneumonia attributable to Pneumocystis jiroveci). Risk factors were assessed by Poisson regression. Results. The study included 3516 persons with HIV infection and 328,738 persons without HIV infection, which provided 23,677 person-years and 2,944,760 person-years of observation, respectively. Incidence rates of pneumonia in HIV-infected individuals decreased from 50.6 hospitalizations per 1000 person-years (95% confidence interval [CI], 42.9-59.7 hospitalizations per 1000 person-years) during 1995-1996 to 19.7 hospitalizations per 1000 person-years (95% CI, 16.2-23.8 hospitalizations per 1000 person-years) during 2005-2007. Compared with control individuals, incidence rate ratios were 34.6 (95% CI, 28.4-41.8) during 1995-1996; 6.3 (95% CI, 5.1-7.7) during 2005-2007; and 5.9 (95% CI, 4.2-7.6) during 2005-2007 for the subgroup with a CD4(+) cell count 1500 cells/mL. Injection drug use, low current CD4(+) cell count, nadir CD4(+) cell count, increasing age, and no current receipt of highly active antiretroviral therapy increased the risk of pneumonia. Conclusions. The risk of pneumonia in persons with HIV infection has decreased substantially since the introduction of highly active antiretroviral therapy, but HIV infection remains a strong risk factor for the need for hospitalization to treat pneumonia, even in persons with high CD4(+) cell counts.