6 - Mycobacteria chimaera infections and their transmission from heater-cooler units

Abstract

The role of heater-cooler units (HCUs) in the transmission of Mycobacterium chimaera during open-heart surgery has been recognized since 2013. Many investigations have uncovered a remarkable global outbreak reflecting the international distribution of implicated devices. HCUs are an essential component of cardiopulmonary bypass operations and their withdrawal would have had severe implications for the patients involved. However, studies have demonstrated that many HCUs are contaminated with a wide range of microorganisms, including M. chimaera and complex biofilms. The ensuing infections were characterized by a poor prognosis and a case fatality rate around 50% despite treatment. Whole genome sequencing of M. chimaera isolates recovered from one manufacturer’s HCUs worldwide has demonstrated a high level of genetic similarity, for which the most plausible hypothesis is a point source contamination of the devices. Dissemination of bioaerosols through breaches in the HCU water tanks is the most likely route of transmission and airborne bacteria have been shown to reach the surgical field even with the use of ultraclean theater ventilation. Controlling the microbiological quality of water circulating in HCUs and reducing biofilm formation have been a major challenge for many hospitals. Enhanced decontamination strategies have been recommended and HCU redesigns were implemented by manufacture to mitigate the risk. Water safety groups in hospitals should be aware that water in medical devices such as HCUs can act as a vector in the transmission of potentially fatal waterborne infections and may have to implement additional control strategies such as removing the HCU from the vicinity of the patient.