Nosocomial bacterial pneumonia in HIV-infected patients : risk factors for adverse outcome and implications for rational empiric antibiotic therapy

Nosocomial bacterial pneumonia (NBP) was once considered a common cause of morbidity and mortality among advanced AIDS patients. However, clinical and microbiological characteristics and outcome-associated risk factors in this population are poorly defined. We conducted a retrospective study of all HIV-infected patients admitted during the period 1988-2002 at the Infectious Diseases Clinic of Milan, Italy, to determine incidence rate and factors affecting mortality of NBP, and to gather clinical and microbiological findings about the condition. We identified 120 episodes of NBP among 4,967 admissions of HIV-infected individuals. A reduction of incidence became evident after the introduction of highly active antiretroviral therapy (HAART). The more common causative agents were Pseudomonas aeruginosa (33%) Staphylococcus aureus (25%) and Streptococcus pneumoniae (21%). Methicillin resistance was frequent among staphylococci (65%). The mortality rate of NBP was 25.8%. Non-statistically significant factors associated with shorter survival were: CD4(+) count < 10 cells/microl, concomitant lung neoplasm, and complicated roentgenographic picture. Only one factor was significantly associated with lower survival, both in univariate and multivariate analysis: a methicillin-resistant Staphylococcus serving as an etiologic agent of pneumonia (RR 4.05; 95% CI, 1.076-15.239; p = 0.039). A decline in incidence of NBP in HIV-infected individuals was observed after introduction of HAART. S. aureus and P. aeruginosa were the leading causes of NBP, but frequency of pneumococcal pneumonia was significant. The sole predictor for mortality was methicillin-resistant Staphylococcus as a pneumonia-causing agent.