Evaluation of PCR-Based Testing for Surveillance of KPC-Producing Carbapenem-Resistant Members of the Enterobacteriaceae Family

Abstract

The spread of carbapenem-resistant members of the Enterobacteriaceae family (CRE) harboring carbapenemases is an emerging public health threat. As KPC-producing Klebsiella species are endemic in our tertiary care hospital, we aimed to evaluate a PCR-based surveillance test for identification of rectal carriage of KPC-producing CRE. We conducted a surveillance study between May and December 2007. Rectal swabs were collected from patients known to harbor CRE and from contacts of newly discovered patients harboring CRE. Specimens were evaluated by culture and by PCR analysis for bla KPC and were defined as positive if CRE was cultured and bla KPC was identified. Discrepant results between the culture and PCR analysis were resolved by subculturing, repeating the PCR, and performing a hydrolysis assay. Positive CRE cultures prior or subsequent to the time of sampling for the study were also taken into consideration. Sensitivity, specificity, and time to result were calculated. A total of 755 swabs were included. Concordant results were documented for 735 specimens; 51 were positive as determined by both PCR and culture. Discrepancies existed for 20 swabs; 9 were bla KPC negative and CRE culture positive, and 11 were bla KPC positive and CRE culture negative. After repeat testing, a total of 64 samples were classified as bla KPC -positive CRE. The sensitivity and specificity of the PCR analysis were 92.2% and 99.6%, respectively, and those of the culture were 87.5% and 99.4%, respectively. Over the last 3 months of the study, the sensitivity of the PCR improved to 96.3%, versus 77.8% for culture. Time to result was 30 h for the PCR and 60 h (negative) and 75 h (positive) for the CRE culture. bla KPC PCR-based testing is a useful method for the surveillance of KPC-producing CRE. Its main advantage over culturing is a shorter time to result, and it may prove to be more sensitive.KPC-mediated carbapenem resistance in members of the Enterobacteriaceae has emerged recently in Israel, as observed in clinical strains of Escherichia coli (14), Enterobacter cloacae (13), and Klebsiella pneumoniae (10). An epidemic clone of KPC-3-producing Klebsiella pneumoniae, possessing resistance to nearly all antimicrobial agents, excluding gentamicin and colistin, has spread in all major Israeli hospitals (15). Infections caused by this strain have been associated with greater than 40% in-hospital mortality (23). As part of our extensive infection control efforts to limit the spread of this highly epidemic strain in the hospital, we aimed to implement a policy of early detection of carriers by screening for gastrointestinal carriage of this pathogen.Active surveillance has been shown to be an effective infection control strategy with other antibiotic-resistant pathogens, such as methicillin (meticillin)-resistant Staphylococcus aureus (4, 5) and vancomycin-resistant enterococci (16). The use of culture-based methods for detection of carbapenem-resistant members of the Enterobacteriaceae family (CRE) from rectal or stool surveillance sampl...

Laboratory and Clinical Evaluation of Screening Agar Plates for Detection of Carbapenem-Resistant Enterobacteriaceae from Surveillance Rectal Swabs

“…Several studies have compared the performances of different culture-based methods, either to direct detection by PCR (8,21,22) or to other culture-based methods (10,13). A summary of these studies is presented in Table 3.…”

“…The study was conducted as part of an ongoing surveillance program that had been implemented at the Tel Aviv Sourasky Medical Center, a 1,200-bed tertiary care hospital in Tel Aviv, Israel. From August 2008 through April 2009, rectal specimens were collected from known CRE carriers and from contacts of patients newly discovered to be harboring CRE, as previously described (22). A nylon flocked swab system with liquid Amies medium was used according to the manufacturer's instructions (Eswab, Copan, Brescia, Italy), immediately transferred to the laboratory following sampling, and processed.…”

“…Isolates nonsusceptible to either imipenem or meropenem were defined as CRE positive and were subjected to PCR for the bla KPC gene according to a previously described protocol (22). PCR-negative isolates were further tested by the modified Hodge test (MHT) according to CLSI recommendations (4).…”

“…The implementation of a reliable and sensitive method for detection of this strain as well as other CRE is therefore critical to the success of infection control measures. Although PCRbased methods have been proven to be highly sensitive and reliable for rapid diagnosis (8,22), these methods require expertise that is not readily available in many centers. Moreover, as the emergence and spread of other types of CRE are increasingly reported (7,19), culture-based methods are still essential for the initial detection of these strains.…”

Risk Factors for Carbapenemase-Producing Carbapenem-Resistant Enterobacteriaceae (CP-CRE) Acquisition Among Contacts of Newly Diagnosed CP-CRE Patients

“…Enterobacteriaceae colonies growing on the selective plates were also tested by PCR for bla KPC throughout the study period and for bla NDM starting in October 2011 using methods previously described. 19,20 Contacts who tested positive were only classified as cases if the carbapenemase detected by PCR matched that of the index patient, even if the organism differed. For example, if the contact and the index had carbapenemase-producing K. pneumoniae, but one had the bla KPC carbapenemase and the other had bla OXA-48 , the contact was not included as a case, ie, the contact was assumed not to have acquired the CP-CRE from that index.…”