Routine active surveillance for carbapenemase-producing enterobacteriaceae from rectal swabs: Diagnostic implications of multiplex polymerase chain reaction

Background: Screening for carriage of carbapenemase-producing Enterobacteriaceae (CPE) is considered an important infection prevention and control strategy. To date, screening has relied primarily on culture although polymerase chain reaction (PCR)-based screening is gaining momentum. Currently there is no gold standard screening method and consequently it is important to consider the implications of different diagnostic strategies used in active surveillance. Aim: To assess the utility of a multiplex PCR screening strategy, as a component of active surveillance, for detection of CPE in patients admitted to various hospitals. Methods: A single rectal swab was collected from patients at various hospitals, considered to be at risk of colonization with CPE. Comparison of a modified US Centers for Disease Control and Prevention culture protocol with a PCR-based assay for the detection of the blaNDM, blaKPC, blaOxA-48-like, blaVIM, blaIMP, and blaGES genes was performed. Findings: Of the 251 consecutive rectal swabs collected, 30 were PCR positive for one or more carbapenemase genes. Fifteen (50%) were culture positive and CPE only accounted for six isolates. PCR demonstrated excellent sensitivity (100%), specificity (89.8%), and negative predictive value (100%) for detection of CPE, but a positive predictive value of only 46.6% and 16.6% for detection of carbapenemase-producing Gram-negatives and CPE, respectively. Conclusion: The apparent excellent performance characteristics of PCR for detection of CPE from rectal swabs must be tempered by knowledge of CPE prevalence and be interpreted within a defined epidemiological context. Further comparative research with culture, evaluating the clinical utility of PCR-based assays as a screening tool, is needed.