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

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There are currently no standardised methods for the sampling and testing of clinical hand wash basin (HWB) samples for the detection of carbapenemase-producing organisms (CPO). Methods of sampling (drain aspirate versus swab from top of drain) and detection of CPO in clinical HWB drains in two different healthcare settings, one which was dealing with a hospital wide outbreak of CPO (hospital A) and another with no reported outbreaks (hospital B) were compared. Drain aspirates and swabs from HWB drains were tested using multiplex PCR together with culture-based methods. No significant difference in detection of CPO 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 direct PCR, and a significantly higher number of carbapenemase genes were detected in hospital A HWB drain aspirate both by PCR and culture (p = 0.014 and 0.0071 respectively). There was a high correlation between drain swab positivity by PCR and culture in hospital A (91%) compared to hospital B where it was only 33%. No difference could be found in drain contamination rates when HWB with rear drain was compared against those with drain directly below the tap. Colonisation of HWB at the top of the drain may be related to risk of cross transmission of CPO from healthcare environment to patients.