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More than one third of the devices that are used in open-heart surgeries may be contaminated with a life-threatening bacteria, putting patients at the risk of deadly infections, a new US study warns. Researchers from the Special Pathogens Laboratory in the US found that 33 out of 89 heater-cooler units (HCU) about 37 per cent tested positive for Mycobacterium chimaera (M chimaera) - a bacterium associated with fatal infections in open-heart surgery patients. HCUs control the temperature of a patient's blood and organs during heart bypass surgery. "The extent of contamination from such a rare organism in multiple units from all over the country was surprising," said John Rihs, from the Special Pathogens Laboratory. Some devices remained positive for M chimera for months, indicating that disinfection can be difficult and routine testing is advisable, researchers said. "Beyond M chimera, we found other NTM species, Legionella and fungi, indicating these units are capable of supporting a diverse microbial population," Rihs said. The team assessed devices already in use for the presence of non-tuberculous mycobacteria (NTM) colonisation (primarily M chimaera) in Heater-cooler units (HCU) before and after decontamination. Researchers tested about 653 water samples from 89 units received from 23 hospitals across the US and Canada. The team was surprised to find how contaminated the units were, with 97 cultures deemed uninterpretable due to high levels of bacterial and fungal contamination. Multiple other strains of mycobacteria were also detected in many of the units. HCUs have water tanks that provide temperature-controlled water during surgery through closed circuits.
The water in the instrument does not come into direct contact with the patient, researchers said. However, the water can aerosolise, and if contaminated, transmit bacteria through the air into the environment, and to the patient, they said. M chimaera is often found in soil and water but is rarely associated with infections. However, patients exposed to the bacteria through open-heart surgery can develop general and nonspecific symptoms that can often take months to emerge. As a result, diagnosis of these infections can be missed or delayed, sometimes for years, making these infections more difficult to treat.