Citywide clonal outbreak of multiresistant Acinetobacter baumannii and Pseudomonas aeruginosa in Brooklyn, NY: the preantibiotic era has returned.

Background: Carbapenems are important agents for treating nosocomial gram-negative infections. Carbapenem-resistant bacteria have become increasingly problematic in certain regions. This study determined the citywide prevalence and molecular epidemiological features of carbapenem-resistant Acinetobacter baumannii and Pseudomonas aeruginosa in Brooklyn, NY.

Methods: All unique patient isolates of A baumannii and P aeruginosa were collected from 15 Brooklyn hospitals from July 1, 1999, through September 30, 1999. Antibiotic susceptibilities, the genetic relatedness of resistant isolates, and the relationship between antibiotic use and resistance rates were determined.

Results: A total of 419 isolates of A baumannii and 823 isolates of P aeruginosa were collected. For A baumannii, 53% were resistant to meropenem and/or imipenem, and 12% were resistant to all standard antibiotics. Ribotyping revealed that a single clone accounted for 62% of the samples and was isolated from patients at all 15 hospitals. The rate of carbapenem resistance was associated with cephalosporin use at each hospital (P =.004). For P aeruginosa, 24% were resistant to imipenem, 5% to amikacin, and 15% to 29% to other antipseudomonal agents. Ribotyping revealed that 3 clones accounted for nearly half of the isolates and were shared by most hospitals.

Conclusions: Approximately 400 patients were infected or colonized with carbapenem-resistant A baumannii and P aeruginosa during a 3-month period in 1999. A few strains have spread widely throughout hospitals in this region. The prevalence of resistant A baumannii seems to be correlated with cephalosporin use. Multiresistant hospital-acquired bacteria should be viewed as a serious public health issue rather than an individual hospital's problem. An intensive coordinated effort will be needed to effectively address this problem.