A factory in Germany has been identified as the source of contamination behind the global outbreak of the slow-growing and potentially fatal Mycobacterium chimaera infection affecting open heart surgery patients exposed to contaminated heater-cooler units used during the procedure.

Researchers in Switzerland were able to trace the pathogen to a LivaNova factory, producers of one of the two most used heater-cooler unit (HCU) brands around the world, using whole genome sequencing.

According to the investigators, the similarity of samples from almost all patients with M. chimaera infection following open-heart surgery strongly points to a common source of infection.

Based on high degrees of similarity between isolates of M. chimaera in these patients’ samples, samples from LivaNova heater-cooler units and from the LivaNova production site, the authors say that it is likely that LivaNova HCUs represent the common source of infection and that contamination occurred during production.

The finding is critical to halting the outbreak, which has already seen over 100 cases of the rare condition confirmed worldwide since July 2015 including four confirmed cases in Australia.

But that number is expected to jump significantly over the next few years – the slow disease course and the need for a specific diagnostic test to isolate and identify the pathogen can delay diagnosis for up to five years.

Investigators warned that the true extent of the current outbreak remains unknown.

“Even if effective public health interventions are implemented now, we should expect more cases to emerge,” they said.

They are also concerned about the risk of hospital-level contamination after they found other strains of M. chimaera in samples taken from hospital tap water, drinking water dispensers and hospital-built HCU systems suggesting clinically relevant infections regularly occur outside of the current outbreak.

Meanwhile, another brand of HCU, Maquet, was also contaminated during production and use and researchers warn that the infectious risk could persist despite controlling contamination at the LivaNova production line.

They added that operating rooms and other hospital settings, especially those with immunocompromised patients, should be cleared of uncontrolled water sources and air-flow producing devices to minimise the risk of infections.