OBJECTIVE: A growing number of Mycobacterium chimaera infections after cardiosurgery have been reported by several countries. These often fatal infections were traced back to contaminated heater-cooler devices (HCDs), which use water as heat transfer medium. Aerosolization of water contaminated with M. chimaera from HCDs enables airborne transmission to patients undergoing open chest surgery. Infection control teams test HCD water samples for mycobacterial growth to guide preventive measures. The detection limit of M. chimaera in water samples, however, has up to now not been investigated.
METHODS: A M. chimaera strain representative of the international cardiosurgery associated M. chimaera outbreak was used to generate a logarithmic dilution series. Two different water volumes, 50ml and 1000ml, were inoculated and after identical processing (centrifugation, decantation, and decontamination) seeded on Mycobacteria growth indicator tube (MGIT) and Middlebrook 7H11 solid media.
RESULTS: MGIT consistently showed a lower detection limit as 7H11 solid media, corresponding to a detection limit of a concentration of ≥1.44x104 CFU/ml for 50ml and ≥2.4 CFU/ml for 1000ml water samples. Solid media failed to detect M. chimaera in 50ml water samples.
CONCLUSION: Depending on water volume and culture method, major differences exist in the detection limit of M. chimaera. In terms of sensitivity, 1000ml water samples in MGIT media performed best. Our results have important implications for infection prevention and control strategies in mitigation of the M. chimaera outbreak and healthcare water safety in general.