Comparison of methods for sampling and detection of carbapenemase-producing organisms in clinical handwash basin drains in health care

There are currently no standardized methods for the sampling and testing of clinical handwash basin (HWB) samples for the detection of carbapenemase-producing organisms (CPOs). Methods used for sampling (drain aspirate vs swab from top of drain) and detection of CPOs in clinical HWB drains in two different healthcare settings, one which was dealing with a hospital-wide CPO outbreak (Hospital A) and another with no reported outbreaks (Hospital B), were compared. Drain aspirates and swabs from HWB drains were tested using multiplex polymerase chain reaction (PCR) together with culture-based methods. No significant difference in detection of CPOs was found between drain aspirate or swab methods of sampling. Direct PCR on samples detected significantly more carbapenemase genes than culture on CARBA agar (P<0.0001 and 0.0045, respectively). A higher percentage of HWB drains were positive in Hospital A both by culture and by direct PCR, and a significantly higher number of carbapenemase genes were detected in HWB drain aspirates at Hospital A, both by PCR and by culture (P=0.014 and 0.0071, respectively). There was high correlation between drain swab positivity by PCR and culture in Hospital A (91%) compared with Hospital B (33%). No difference in drain contamination rates was found when HWBs with a rear drain were compared with HWBs with the drain directly below the tap. Colonization of HWBs at the top of the drain may be related to risk of cross-transmission of CPOs from the healthcare environment to patients.