Epidemiology, Treatment, and Outcomes of Nosocomial Bacteremic Staphylococcus aureus Pneumonia

Nosocomial pneumoniaNosocomial pneumonia is currently the second most common hospital infection and is the leading cause of death from hospital-acquired infections. The incidence of acquiring nosocomial pneumonia ranges from 7.8 to 68.0%, and is influenced by the duration of hospital and ICU stay, the specific diagnostic method used for pathogen detection, and the patient population studied. The rate of nosocomial pneumonia secondary to Staphylococcus aureus has increased steadily over the past 2 decades. In one review of three major studies examining the etiology of ventilator-associated pneumonia (VAP), S aureus was the most frequently isolated Gram-positive organism and the second-most isolated organism only behind Pseudomonas aeruginosa. Most studies estimate that S aureus accounts for 15 to 35% of all nosocomial pneumonia cases; however, the true incidence depends on many factors, such as patient demographics, local susceptibility patterns, and methods of diagnosis.

Although there is increased recognition of S aureus as a major pathogen causing nosocomial pneumonia, there are few studies with descriptive data specifically evaluating patient outcomes of S aureus pneumonia. In addition, in the last decade, evidence has accumulated demonstrating that initial inappropriate antibiotic treatment is an important independent predictor of excess mortality in patients with nosocomial pneumonia. To our knowledge, no data exist examining the impact of delayed appropriate antibiotic treatment specifically for bacteremic S aureus pneumonia. In a retrospective study evaluating S aureus bacteremia, a delay in treatment with antibiotics for > 44.75 h was found to be an independent predictor of infection-related mortality (IRM) [adjusted odds ratio, 3.8; 95% confidence interval, 1.3 to 11.0; p = 0.01]. It is unknown if this 44.75-h breakpoint is applicable to patients with bacteremic S aureus pneumonia. Although the impact of methicillin resistance on the outcomes of patients with S aureus bacteremia has been extensively evaluated, little information exists on the impact of the methicillin resistance of patients with nosocomial bacteremic S aureus pneumonia (NBSAP). Furthermore, less information exists on the impact of empirical antibiotic selection on NBSAP. Over the past few years, studies have suggested that vancomycin may not be optimal for the treatment of S aureus pneumonia, especially in the subset of patients who have been infected with methicillin-resistant S aureus (MRSA). To evaluate the epidemiology, treatment, and outcomes of NBSAP, a retrospective cohort analysis was performed. Specifically, we examined the impact of methicillin resistance, empirical therapy, and delayed treatment on the outcomes of patients with NBSAP.