Resistant Pathogens Causing Ventilator-Associated Pneumonia Reported to the CDC's National Healthcare Safety Network, January 2007-June 2010

Background:  The emergence of antimicrobial resistance among bacterial pathogens causing healthcare-associated infections (HAIs) in U.S. hospitals is a major problem. Resistance may be particularly prevalent in intensive care units (ICUs), where ventilator-associated pneumonia (VAP) is a commonly encountered HAI.

Objective:  To evaluate changes in antimicrobial resistance over time among pathogens causing VAP reported to CDC's National Healthcare Safety Network (NHSN).

Methods:  We evaluated isolates identified as pathogens for VAP events reported to NHSN from January 2007-June 2010. Data from adult and pediatric ICU and non-ICU locations were included; neonatal ICUs were excluded. The most commonly reported VAP pathogen-antimicrobial combinations (phenotypes) were selected: methicillin-resistant (MR) Staphylococcus aureus (SA); piperacillin- or piperacillin/tazobactam-resistant (PR) Pseudomonas aeruginosa (PA); carbapenem-resistant (CR) PA; extended-spectrum cephalosporin-resistant (ESCR) Klebsiella pneumoniae (KP); CR KP; and CR Acinetobacter baumannii (AB).  We divided the number of resistant isolates by the number of tested isolates for each phenotype to determine the resistant proportion.  For each phenotype we used generalized linear regression to assess changes in the resistant proportion from 2007 through the first six months of 2010. Changes were assessed in all facilities that reported ≥1 VAP at any time from January 2007-June 2010 and in the subset of facilities that reported ≥1 VAP in each of the 4 calendar years.

Results:  A total of 13,522 pathogens were reported from 10,526 VAP events in 579 facilities in 46 states. Most VAP events (97%) were reported from ICUs. Of 13,522 pathogens, 7772 (57.5%) were SA, PA, KP or AB. In the analysis including all facilities reporting ≥1 VAP during the study period, there were no significant changes in the proportions of SA isolates that were MR, PA isolates that were PR or CR, or KP isolates that were CR; however, there were significant increases in the proportions of KP isolates that were ESCR (from 19.6% in 2007 to 36.7% in the first six months of 2010) and AB isolates that were CR (from 31.4% in 2007 to 66.3% in the first six months of 2010) (Figure). These findings were confirmed in the subset analysis.

Conclusions:  Four bacterial species accounted for more than half of all VAP pathogens reported to NHSN from January 2007-June 2010. Resistance to selected key antimicrobial agents was prevalent among these pathogens, and increased significantly in KP and AB isolates. More work is needed to determine risk factors for infection due to resistant gram-negative pathogens and identify strategies to limit their spread.