Reemergence of Mycobacterium chimaera in Heater-Cooler Units despite Intensified Cleaning and Disinfection Protocol

Abstract

Invasive Mycobacterium chimaera infections after open-heart surgery have been reported internationally. These devastating infections result from aerosols generated by contaminated heater-cooler units used with extracorporeal circulation during surgery. Despite intensified cleaning and disinfection, surveillance samples from factory-new units acquired during 2014 grew nontuberculous mycobacteria after a median of 174 days.

Keywords: Mycobacterium chimaera; bacteria; disinfection; heater–cooler units; hospital equipment; hospital infections; nontuberculous mycobacterial infections; nosocomial infections; tuberculosis and other mycobacteria.

Figure 1

Custom-made stainless steel housing for heater–cooler units (model 3T; Sorin [now LivaNova, London, UK]) used at the University Hospital Zurich, Zurich, Switzerland. A) Front view shows the fine dust filter F7 over the air inlet (arrow). B) Side view shows the half-open back door with the rectangular opening (arrow), through which a duct connects the housing to the operating room ventilation exit. The negative pressure of the operating room ventilation system generates the necessary airflow.

Figure 2

Results of heater–cooler unit (HCU) water surveillance cultures by year and month, University Hospital Zurich, Zurich, Switzerland. The dashed vertical line shows the date of implementation of the intensified protocol (i.e., mid-April 2014). The vertical arrows indicate the start of use of each factory-new HCU in the operating room. HCU 3, HCU 4, and HCU 5 were serviced with the intensified in-house maintenance from the time of delivery. HCU 4 was sent for repair at the manufacturer during December 2014–September 2015. Results of mycobacterial cultures are shown for each HCU. No indicates a negative culture for nontuberculous mycobacteria (NTM), indicated by X. Yes indicates a positive culture for NTM. Filled circles indicate Mycobacterium chimaera; empty circles indicate NTM other than M. chimaera. As per date indicated, cultures were reported as positive if ≥1 water sample (1 sample from cardioplegia and 1 sample from patient circuit were gathered at each date) grew NTM. For missing data points (i.e., no negative or positive results shown), mycobacterial cultures could not be tested because of bacterial overgrowth or lack of availability of the HCU.