Multidrug-resistant Enterobacteriaceae pose a serious infection control challenge and have emerged as a public health threat. We examined national trends in the proportion of Klebsiella pneumoniae isolates resistant to carbapenems (CRKP) and third-generation cephalosporins (G3CRKP).

Retrospective analysis of approximately 500,000 K. pneumoniae isolates cultured between January 1999 and July 2010 at 287 clinical laboratories throughout the United States.

Isolates were defined as CRKP if they were nonsusceptible to 1 or more carbapenems and were defined as G3CRKP if they were nonsusceptible to ceftazidime, ceftriaxone, or related antibiotics. A multivariable analysis examined trends in the proportion of resistant isolates, adjusting for age, sex, isolate source, patient location, and geographic region.

The crude proportion of CRKP increased from less than 0.1% to 4.5% between 2002 and 2010; the frequency of G3CRKP increased from 5.3% to 11.5% between 1999 and 2010. G3CRKP and CRKP were more common among elderly patients (those greater than 65 years of age); the adjusted odds ratio (aOR) relative to pediatric patients (those less than 18 years of age) was 1.2 for G3CRKP (95% confidence interval [CI], 1.2–1.3) and 3.3 for CRKP (95% CI, 2.6–4.2). G3CRKP and CRKP were also more common among patients from the northeastern United States (aOR, 2.9 [95% CI, 2.8–3.0] and 9.0 [95% CI, 7.9–10.4]) than among those from the western United States. The prevalence of outpatient CRKP isolates increased after 2006, reaching 1.9% of isolates in our sample in 2010 (95% CI, 1.6%–2.1%).

The frequency of G3CRKP and CRKP is increasing in all regions of the United States, and resistance is emerging among isolates recovered in the outpatient setting. This underscores the need for enhanced laboratory capacity and coordinated surveillance strategies to contain the further spread of these emerging pathogens.