pseudomonas aeruginosa nosocomial pneumonia 1195
table 5. Independent Risk Factors of Inappropriate Initial Antibiotic Therapy Community-onset pneumonia Hospital-acquired pneumonia Ventilator-associated pneumonia
Variable Prior antibiotic admission
Charlson comorbidity score (increasing increments of 1) Multidrug-resistant isolate Bacteremia
11.15 7.11–17.48 <.001 3.66 2.28–5.89 1.92–5.33
3.2 .022
NOTE. Hosmer-Lemeshow/ area under the receiver operating curve: community-onset pneumonia, 0.453/0.691; hospital-acquired pneumonia, 0.721/0.641; ventilator-associated pneumonia, 0.731/0.609. AOR, adjusted odds ratio.
of Pa-NP in order to assess the impact of pneumonia classifi- cation on outcomes. By focusing on a single pathogen we have a more homogeneous population in order to minimize pathogen-related confounders. Nevertheless, our findings are consistent with those from studies examining NP attributed to heterogeneous pathogens. Quartin et al24 performed a post hoc analysis of a randomized antibiotic treatment trial in 1,184 patients. Compared with patients with HAP or VAP, patients with COP were older, had slightly higher severity scores, and were more likely to have comorbidities. P. aerugi- nosa was the most common gram-negative organism isolated in all pneumonia classes (COP,11.1%; HAP, 7.4%; VAP, 9.4%). Piskin et al25 examined 348 patients with HAP or VAP and found that risk factors for IIAT varied by their pneumonia type. Multiple logistic regression analysis revealed that the risk factors for inappropriate initial therapy in HAP were late-onset infection and greater APACHE II scores whereas in VAP antibiotic usage in the previous 3 months and admission to a surgical unit were found to be independent risk factors for IIAT. Taken together with our data, these studies highlight the difficulty in identifying consistent clinical markers for out- come in NP across pneumonia categories. A large volumeof research has emphasized the importance of
almost one-third of Pa-NP had onset in the community setting and that the rates of MDR and IIAT were similar for COP compared with HAP and VAP, being approximately one-third and one-quarter respectively. Moreover, patients with COP had the highest rates of previous hospitalization, placing them at greater risk for infection with healthcare-associated pathogens. This highlights the importance of correctly identifying patients at risk for Pa-NP, regardless of the location and conditions of their pneumonia, in order to provide optimal medical treatment for potentially antibiotic-resistant isolates. Our study is unique in providing the largest cohort to date
early appropriate antimicrobial therapy for serious infections in order to minimize the risk of death.26–30 It has also been shown that escalation of treatment from IIAT to an appropriate anti- biotic regimen in response to culture results fails to mitigate this increase in the risk of death.31,32 Our findings generally confirm these relationships. IIAT was found to be a predictor of hospital death in VAP where patients with VAP had the greatest severity
of illness and prevalence of septic shock. The potential practical implications of these findings are illustrated by a recent large epidemiologic study from the United States that identified 205,526 patients with P. aeruginosa infections (187,343 pneumonia; 18,183 bloodstream infection) and 95,566 patients with Enterobacteriaceae infections (58,810 pneumonia; 36,756 bloodstreaminfection).33 The prevalence ofMDR P. aeruginosa was approximately 15-fold higher than carbapenem-resistant Enterobacteriaceae and there was a net rise in MDR P. aeruginosa as a proportion of all P. aeruginosa infections from 2000 to 2009. A recent meta-analysis also demonstrated that MDR status was an important determinant of mortality due to nosocomial infections attributed to gram-negative bacteria, where P. aeruginosa and Acinetobacter species were the most common isolates.34 It is also interesting that the observed mortality for COP was lower than that observed more than 10 years ago despite the high rate of bacteremia, suggesting that these may have been less virulent strains of gram-negative bacteria.35 The high rates of MDR and IIAT in Pa-NP for all pneu-
monia types mandate that clinicians have therapeutic strategies in place to optimize therapy. Scoring systems to identify patients with MDR infections, including MDR P. aeruginosa, are available but limited in their overall ability to predictMDR infection.23,36,37 A number of novel methods aimed at improving the early identification of pathogens and related antibiotic susceptibilities are also entering the diagnostic arena. Such technological advances offer a strategy that could potentially maximize the administration of appropriate antibiotic therapy while minimizing unnecessary antibiotic exposure. One such approach employs advanced automated microscopy techniques that allow the identification of bacterial species, the determination of the presence of antibiotic resis- tance genes, and bacterial killing by specific antibiotics within 4 to 6 hours using direct specimen inoculation.38 Our study has a number of limitations. First, it was limited to
AOR 95% CI P value AOR 95% CI
P value AOR 95% CI 0.39–0.73
0.54 1.17
.006 1.11–1.23
P value .043
.003
an evaluation of Pa-NP and the findings may not be applicable to NP attributed to other pathogens. Second, the criteria for establishing a diagnosis of Pa-NP varied across centers. There- fore, our study cohort could have included patients without true pneumonia. Third, by analyzing each category of pneumonia separately we have limited our ability to identify all important
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