Interventional cardiology

Cardiologists advised to be alert for rare infection


An outbreak of Mycobacterium chimaera (M. chimaera) infection associated with contaminated heater cooler units used for cardiac bypass surgery has sparked warnings from infectious disease specialists for doctors to ‘remain vigilant’ about detecting and managing new cases of the rare and potentially fatal infection.

Overseas there have been 70 confirmed cases, two confirmed cases in New South Wales and one case in Queensland.

All three patients had undergone open-heart surgery in which the contaminated equipment – the Stӧckert 3T heater cooler unit (HCU) – was used.

The most recent Australian infection reported last month involved a man in his 40’s who contracted the slow growing infection from a surgical HCU at Prince of Wales Hospital, the same hospital involved in the first NSW case reported in September last year.

According to NSW Health, the contaminated equipment has been removed from several hospitals as a precaution.

While infectious disease specialists in Australia say the risk of infection following cardiac bypass surgery here is low, the long incubation period and unusual non-specific symptoms mean that cardiologists need to know when to suspect the condition and how to diagnose it.

Writing in the MJA this week, infectious diseases physician Professor Andrew Stewardson from Austin Health in Melbourne said the infection should be considered in patients who have previously undergone surgery with cardiopulmonary bypass and who present with cardiac or disseminated infection or sternal wound infection that is unresponsive to standard antibiotic therapy.

Other clinical presentations that could indicate M. chimaera infection include prosthetic valve endocarditis, prosthetic vascular graft infection, or early prosthetic valve failure.

Cardiologists should also keep in mind that any of these complications could crop up months or years after a bypass procedure, Professor Stewardson warned.

Doctors who suspect possible infection should have an invasive sample taken and sent for testing. Once a diagnosis is confirmed, doctors should also notify their hospital infection and control team, Professor Stewardson added.

Speaking to the limbic Dr Chris Coulter, Director of Queensland Health’s Mycobacterium Reference Laboratory said optimal medical treatment for the condition still remains unclear and doctors should work with an infectious diseases physician to manage patients.

At the moment treatment recommendations are based on experience of a related bacterial infection, Mycobacterium avium, in severely immunosuppressed HIV-infected patients, or on case series reports.

Patients diagnosed with the infection must undergo extensive combination antimicrobial therapy for at least 12 months, which consists of clarithromycin, ethambutol and rifabutin or rifampicin as a third agent, all of which can be administered orally, Dr Coulter told the limbic.

They will need to be closely monitored throughout the course of treatment, he advised, because adverse drug effects, like ocular toxicity from ethambutol, are common and drug interactions are also potentially significant.

“In cases where prosthetic material becomes infected, cure is unlikely to occur without removal and replacement of the prosthetic material,” he added.

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