Descriptive Epidemiology of a Voluntary Convenience Sample of Carbapenem-Resistant Enterobacteriaceae Isolates Submitted to the Pennsylvania State Public Health Laboratory, 2009 to 2014

BACKGROUND:   Carbapenem-resistant Enterobacteriaceae (CRE) infections remain a serious threat to public health. Four carbapenemases have been identified in Pennsylvania, including Klebsiella pneumoniae carbapenemase (KPC, found in 47 states); New Delhi Metallo-beta-lactamase (NDM, 16 states); and Verona Integron-Encoded Metallo-beta-lactamase (VIM, 4 states). CRE are voluntarily reportable in many states, including Pennsylvania. Prior to 2014, no Pennsylvania statewide electronic database of CRE isolates was maintained. The purpose of this study was to evaluate a voluntarily submitted convenience sample of CRE isolates submitted to the Pennsylvania state public health laboratory. This was accomplished by creating an electronic database of CRE results and performing descriptive epidemiology of submitted isolates.

METHODS:   All gram-negative, human isolates voluntarily submitted for CRE testing to the Pennsylvania state public health laboratory from March 2009 through May 2014 were identified. Laboratory testing was performed by the Centers for Disease Control and Prevention. Because most isolates were submitted during and prior to 2012, the pre-2012 CRE case definition was used for all isolates. Isolates were tested for resistance for up to four carbapenems (doripenem, ertapenem, imipenem, meropenem) and four carbapenemases (KPC, NDM, VIM, and the oxacillinase group of beta-lactamase (OXA)) by PCR. The Modified Hodge test and Extended-spectrum beta-lactamase testing was also performed. Data were managed and analyzed using SAS 9.3 and Epi Info 7.1.3.

RESULTS:   Of the 175 isolates submitted, 54% were from female patients. Median patient age was 69 years (range: 2-98 years). Most specimens were from non-sterile sites, including urine (56%) and wounds (12%). Specimens were submitted by hospital (67%), commercial (31%) and public health laboratories (1%). Of isolates tested, 79% were resistant to ≥1 carbapenem and 83% showed the presence of ≥1 carbapenemase (KPC: 73/119 isolates (61%), NDM: 6/63 (10%), OXA: 1/1 (100%), VIM: 1/1 (100%)). Resistant isolates were identified in 28 of 67 Pennsylvania counties, reflecting wide geographic distribution; however, southwestern Pennsylvania was under-represented. Frequently identified organisms included Klebsiella pneumoniae (52%), Enterobacter cloacae (15%), Escherichia coli (11%), and Enterobacter aerogenes (8%).

CONCLUSIONS:   Carbapenem-resistant Enterobacteriaceae were identified in 42% of Pennsylvania counties and 79% percent of tested isolates showed resistance to ≥1 carbapenem. CRE are an emerging disease in Pennsylvania and throughout the United States. Because treatment is difficult, prevention remains critical to CRE control. Further statewide evaluation of CRE in Pennsylvania, including a survey of hospitals, long-term care facilities and clinical laboratories, is ongoing.