Carbapenem-resistant Enterobacteriaceae, 2011

Enterobacteriaceae are a large family of Gram-negative bacilli (GNB) that can cause community- and healthcareassociated infections. Carbapenem resistant Enterobacteriaceae (CRE) are resistant to most available antibiotics. Some CRE bacteria harbor resistance genes that produce chromosomally- or plasmid-mediated enzymes known as carbapenemases. Plasmid-mediated carbapenemases, such as the Klebsiella pneumoniae carbapenemase (KPC), can easily spread between bacteria of similar species.

KPC is the most common plasmidmediated carbapenemase found in the United States. Since 2009, several types of metallo-β-lactamase (MBL)- producing Enterobacteriaceae have been reported in the United States, including New Delhi MBL (NDM) and Verona Integron-encoded MBL (VIM). MBL-producing bacteria are more common outside the United States.

CRE infections most commonly occur among patients with co-morbid conditions, invasive devices, and who have received extended courses of certain antibiotics.

MDH first detected a KPC-producing Enterobacteriaceae isolate in February 2009, and began statewide passive CRE surveillance. As part of this surveillance, laboratories submit isolates from CRE cases to the PHL for further characterization.

In 2011, we adopted a standardized CRE case definition developed by CDC and states participating in the EIP Gram-negative Surveillance Initiative. This CRE definition includes Enterobacteriaceae that are nonsusceptible to a carbapenem (excluding ertapenem) and resistant to all tested third generation cephalosporins (2011 CSLI breakpoints).

During 2011, 44 cases of CRE were reported. The median age of cases was 58 years (range, 1 month to 91 years); 20 (45%) were male and 23 (52%) were residents of the metropolitan area. Urine (25) was the most common source followed by respiratory tract (7), peritoneal fluid (5), blood (4), wound (2), and other body fluid (1). Two isolates of different species were detected in 1 case; CRE species varied: 33/44 (75%) were represented by E. cloacae (23) and K. pneumoniae (10). Twenty-one (48%) cases were hospitalized at the time of culture (12 hospitalized >3 days prior to culture); median length of stay (LOS) was 27 days (range, 2 to 238). Twenty-three (52%) cases were identified in other health care settings including ER/ outpatient clinics (15), long-term acute care hospitals (6), and long-term care facilities (2).

Forty-one isolates from 40 cases were tested by PCR for the blaKPC gene; 21 (51%) were KPC positive. Of these, 12 (57%) were cultured from urine, 5 (24%) respiratory tract, 2 (9%) blood, 1 (5%) peritoneal fluid, and 1 (5%) other body fluid. KPC-positive isolates were E. cloacae (11), K. pneumoniae (9), and C. freundii (1). The median age of KPC positive cases was 64 years (range, 6 months to 91 years); 9 (43%) were male; 11 (52%) were residents of the metropolitan area; and 9 (43%) were hospitalized at the time of culture (6 hospitalized >3 days prior to culture). Median LOS was 27 days (range, 5 to 238). Other cases were detected in ER/ outpatient clinics (5), long-term acute care hospitals (6), and long-term care facilities (1).

Two KPC-negative isolates (1 E. coli and 1 K. pneumoniae) were confirmed NDM positive by CDC. Both isolates came from a single outpatient urine culture. This case had recently returned to the United States after being hospitalized during a trip to India where NDM is known to be present in hospitals.

In summary, approximately half of the CRE cases reported were KPC positive. Active surveillance testing should be considered when a patient with previously unrecognized CRE or hospital-onset CRE infections is identified. No outbreaks or transmission of CRE were reported among facilities that conducted active surveillance testing during 2011.

• For up to date information see>> "Superbugs": Carbapenem-resistant Enterobacteriaceae (CRE)
  
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2011