4-hour immuno-chromatographic detection of intestinal carriage of carbapenemase-producing Enterobacteriaceae : a validation study.

Background. The increasing incidence of Carbapenemase-Producing Gram-Negative Bacilli (C-PGNB) represents a major public health challenge. Rapid detection of the digestive colonization with C-PGNB is fundamental to control their spread. Aim. Validation of a rapid protocol for C-PGNB detection directly on rectal swabs. Methods. We developed a protocol combining enrichment by a rapid selective subculture of the rectal swab medium and realization of a Resist-4 OKNV K-SeT® test on the bacterial pellet so obtained. The limit of detection and performances of this protocol were validated in vitro on 52 C-PGNB strains spiked on calibrated sample suspension; and confirmed in clinical settings on 144 rectal swabs sampled from patients with C-PGNB digestive colonization (n=48) and controls (patients with ESBL colonization (n=48) and without carbapenemase/ESBL (n=48)). Results. The protocol detected with 100% sensitivity the presence of the 15 OXA-48-, 14 KPC-, 13 NDM- and 10 VIM-producing GNB from 103 CFU/mL. The limit of detection was 2.102 CFU/mL. Among the 48 C-PGNB containing rectal swabs of the validation cohort, 46 were accurately detected. False negative were observed for 1 NDM-producing Acinetobacterbaumanii and 1 OXA-48-producing E. coli. The 96 control swabs were negative. Sensitivity and specificity for C-PGNB detection were 97.7% 95%CI(87.7-100) and 100% 95%CI(96.2-100). The negative likelihood ratio was 0.04 95%CI(0.01-0.16). Considering a C-PGNB digestive colonization prevalence between 0.01% and 0.1%, positive and negative predictive values were 100%. Conclusion. Our protocol is a rapid and low-cost method detecting accurately the digestive colonization with C-PE in 4 hours without any requirement for specific equipment.