Multicenter Evaluation of the Xpert Carba-R Assay for Detection and Identification of Carbapenemase Genes in Sputum Specimens

摘要

Rapid diagnosis of infections caused by carbapenem-resistant Enterobacteriaceae (CRE) is crucial for proper treatment and infection control. The Xpert Carba-R assay is a qualitative multiplex real-time PCR method that qualitatively detects and differentiates five common carbapenemase genes (bia(KPC), bla(ND)(M), bla(VIM), bla(OXA-)(48), and bla(IMP)) directly from rectal swabs or purified colonies within approximately 1 h. We performed a multicenter evaluation of the investigational use of the Carba-R assay for detection and differentiation of carbapenemase genes from sputum specimens in patients with a clinical diagnosis of pneumonia. The intra- and interassay coefficients of variation values for the Carba-R assay were 0.2 to 2.0 and 1.4 to 2.3, respectively. A total of 301 sputum specimens were collected and tested. Compared to bacterial culture followed by PCR identification of resistance genes from colonies, the Carba-R assay reduced turnaround time from 56 to 84 h to less than 2 h. Carbapenemase genes were detected by the Carba-R assay in Klebsiella pneumoniae (n = 236), Escherichia coil (n = 22), Enterobacter cloacae (n = 23), Klebsiella oxytoca (n = 8), Serratia marcescens (n = 6), Citrobacter freundfi (n = 4), and Klebsiella aerogenes (n = 2). The Carba-R assay detected 112 bla(KPC) (33.5), 70 bla(NDM) (21.0), 8 bla(IMP) (2.4), and 2 bla(VIM) (0.6) genes, with positive percent agreement, negative percent agreement, and concordance rates of 92.9, 86.7, and 88.3, respectively, for the dominant bla(KPC) and 85.0, 87.8, and 87.4, respectively, for the bla(NDM) genes. Neither method detected the bla(OXA-)(48) carbapenemase gene. The convenient, rapid, and simple characteristics of the Xpert Carba-R assay make it a potential tool for CRE detection and identification directly in sputum specimens.