S. aureus is increasingly implicated as a cause of ventilator-associated pneumonia (VAP), and many S. aureus isolates in the intensive care unit (ICU) are now resistant to methicillin (MRSA). Nonetheless little is known about the impact of S. aureus, generally, and MRSA, specifically, on outcomes for patients with VAP.
We retrospectively explored a large, multi-institutional database (ATLAS) to identity patients with VAP during 2002. The dataset includes patient level information regarding: diagnosis, culture results, severity of illness, length of stay, hospital charges, and outcomes. Subjects with VAP were identified based on a principal or secondary diagnosis of pneumonia and a new, positive bacterial culture identified after at least 24 hours of mechanical ventilation. We compared morbidity and mortality in patients with VAP due to MRSA and methicillin sensitive S. aureus (MSSA) to subjects with VAP caused by other pathogens.
During the study period, there were 306 cases of culture-confirmed VAP with 100 (32.7%) due to S. aureus. Approximately 1/3rd of these isolates were MRSA. The unadjusted mortality rates in those with MRSA were not significantly different from persons with MSSA (32.4% vs. 38.1%, p = 0.50). However, mortality among all patients with S. aureus (MRSA or MSSA) was higher than that in patients with other bacterial pathogens (36.0% vs. 24.1%, p = 0.04). The median hospital length of stay was longer in patients with MRSA than MSSA (21 days vs. 15 days, p = 0.03). The median total hospital charges for caring for MRSA reflected this and were higher than charges for treating MSSA VAP: $115,885 vs. $86,334.
S. aureus remains a major cause of VAP. MRSA VAP is associated with both excess mortality and cost.
Better preventive efforts to contain MRSA in the ICU are needed. The disproportionate adverse impact of MRSA VAP on clinical outcomes suggests that current treatment alternatives may be sub-optimal.
A.F. Shorr, Pfizer Inc.