Key Point

Production of MBL-PA in patients with hospital-acquired pneumonia had a significant effect on 30-day mortality, especially in patients with ventilator-associated pneumonia.

PORTO ALEGRE, BRAZIL—In patients with hospital-acquired pneumonia, metallo-ß-lactamase-producing Pseudomonas aeruginosa (MBL-PA) resulted in a significant increase in mortality.¹ This mortality increase was observed particularly in patients with ventilator-associated pneumonia.

Alexandre P. Zavascki, MD, Infectious Diseases Instructor at Hospital São Lucas da Pontifícia Universidade Católica do Rio Grande do Sul in Porto Alegre, Brazil, and colleagues examined 150 patients with P aeruginosa hospital-acquired pneumonia. Forty-two of these patients had MBL-PA hospital-acquired pneumonia; 30-day mortality in this group was 57.1% (24 patients). Among the remaining 108 patients without MBL-PA hospital-acquired pneumonia, 30-day mortality was 29.6% (32 patients). For all 150 patients, the 30-day mortality rate was 37.3%. Among the 22 patients with MBL-PA ventilator-associated pneumonia, 30-day mortality was 77.3% (17 patients), while it was 48.5% (16 patients) among the 33 ventilator-associated pneumonia patients who did not have MBL-PA. The 55 patients with ventilator-associated pneumonia had a 30-day mortality rate of 60%.

PREDICTORS OF MORTALITY AMONG PNEUMONIA PATIENTS

Thirty-day mortality was significantly associated with a higher Charlson comorbidity score, presentation with severe sepsis or septic shock, ventilator-associated pneumonia, and appropriate antimicrobial treatment. Of these independent factors, presentation with severe sepsis or septic shock and ventilator-acquired pneumonia had the largest impact on 30-day mortality. MBL production achieved statistical significance only before the inclusion of appropriate antimicrobial treatment. Survivors with MBL-PA hospital-acquired pneumonia were in need of vasoactive drug therapy for a significantly longer time than were survivors without MBL-PA. Although survivors with MBL-PA hospital-acquired pneumonia were in need of mechanical ventilation longer than survivors without MBL-PA, this association did not achieve statistical significance.

Dr. Zavascki and colleagues stated that the effect of MBL-PA causing an increase in the already high mortality rate of patients with hospital-acquired pneumonia "was probably mediated by a more frequent inappropriateness of antimicrobial therapy for MBL-PA infections, considering that MBL production was not significantly associated with 30-day mortality when the variable administration of appropriate therapy was included in the multivariate analysis."

Although no statistically significant effect of early appropriate therapy on mortality was shown, "crude analysis" revealed lower mortality rates for patients who started treatment earlier, especially within 72 hours. However, the researchers pointed out the possibility that their sample size was not large enough for differences to be detected within the 72-hour period. "Since early therapy is recognizably associated with better outcomes, we emphasize its importance and attribute, at least partially, the lack of statistical significance in our multivariate model" to the relatively small sample size, the researchers stressed.

Dr. Zavascki and colleagues also noted, "Worrisome high mortality rates were observed among patients with MBL-PA [hospital-acquired pneumonia] despite appropriate therapy, particularly among those with [ventilator-associated pneumonia]." In a group of eight patients receiving aztreonam monotherapy, there were two deaths, which presented the lowest mortality rate among appropriate treatments for MBL-PA hospital-acquired pneumonia. However, all patients with ventilator-associated pneumonia who took aztreonam monotherapy died, and no significant associations were observed between any antibiotic and lower mortality. "Nevertheless, owing to the relatively small sample size, no definitive conclusion about superiority of any antibiotic for treatment of MBL-PA [hospital-acquired pneumonia] can be made," the research team stated.

—John Merriman

Reference
1. Zavascki AP, Barth AL, Fernandez JF, et al. Reappraisal of Pseudomonas aeruginosa hospital-acquired pneumonia mortality in the era of metallo-ß-lactamases-mediated multidrug resistance: a prospective observational study. Crit Care. 2006;10:R114.

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