Ventilator-Associated Pneumonia in the National Nosocomial Infections Surveillance System and the National Healthcare Safety Network: Analysis of Incidence and Pathogen Distribution, 2002-2008

Background: Ventilator-associated pneumonia (VAP) is common among mechanically ventilated patients and is associated with poor outcomes. In recent years some U.S. healthcare facilities have reported declining VAP incidence rates following implementation of prevention measures, such as the ventilator bundle. Whether VAP incidence rates have declined on a larger scale among facilities reporting data to CDC since revised pneumonia surveillance definitions were implemented in 2002 is not known.

Objective: To compare VAP incidence rates and pathogen distribution in intensive care units (ICUs) reporting data to the National Nosocomial Infections Surveillance (NNIS) system (2002-2004) and the National Healthcare Safety Network (NHSN) (2006-2008).

Methods: VAPs reported from selected ICU types were included; NHSN VAPs were included where denominator data were not missing. Demographic and clinical characteristics were described and pathogen distributions compared for monomicrobial VAPs reported in 2002-2004 and 2006-2008 using χ² tests. Pooled mean incidence rates were calculated; changes in pooled mean rates over time in medical, medical/surgical and surgical ICUs were analyzed using Poisson regression.

Results: Of 22092 VAP events, 13356 (60%) were from 239 facilities reporting to NNIS and 8736 (40%) were from 444 facilities reporting to NHSN. Most VAPs (18175, 82%) occurred ≥ 5 days after hospital admission, and 14009 (63%) were monomicrobial. Overall, 4216 patients (19%) died. Although Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter baumannii were the 3 most common pathogens causing monomicrobial VAP in both the NNIS and NHSN periods, S. aureus was significantly less prevalent in 2006-2008 than in 2002-2004 (28% vs. 31%, p=0.0003) and A. baumannii was significantly more prevalent in 2006-2008 than in 2002-2004 (9% vs. 7%, p<0.0001). Incidence rates in medical, medical/surgical and surgical ICUs declined significantly from 2002-2008 (Figure). When the analysis was restricted to continuous reporters (units reporting for ≥1 month in each year of the study period), annual declines in these ICU types remained significant (-11% to -21%).

Conclusions: Declines in VAP incidence over the past several years may be due in part to heightened awareness of VAP as a cause of preventable harm in ICU patients and implementation of prevention measures. Additional research is needed to reduce the burden of VAP surveillance, improve the accuracy of surveillance definitions, and identify effective prevention strategies.