Mycobacterium chimaera in heater cooler devices

Mycobacterium chimaera, one of the non-tuberculous mycobacteria (NTM), is a slow growing environmental organism. It is usually of low pathogenicity and is an occasional cause of pulmonary infection in immune compromised patients.

M. Chimaera and heater cooler devices

Since being reported in Switzerland, there has been a number of M. chimaera infections (predominantly prosthetic valve endocarditis) reported from countries in Europe and the USA related to the use of heater-cooler devices (HCDs).

These devices are used to regulate the temperature of the patient’s blood during cardiopulmonary bypass surgery. The transmission route from the HCD to the patients appears to be linked to biofilm that develops inside the unit’s water reservoir, allowing growth of environmental bacteria such as M. chimaera. The microorganisms are subsequently aerosolised into the theatre environment by the unit’s fan during use.

Infections with M. chimaera have predominantly been associated with HCDs from one manufacturer (LivaNova, formerly Sorin, Germany). The Sorin 3T HCDs have been used at all hospitals in Western Australia (WA) that perform cardiac bypass surgery.

What is the health system response?

The Therapeutic Goods Administration (TGA) first issued a Medical Devices Safety Update in May 2016, advising of the issue and listing recommended actions that hospitals should take. A further update was issued in October 2016 confirming one case of M. chimaera infection in a Queensland patient that was potentially linked to a contaminated unit. Second case has been reported from New South Wales in January 2017. There have been no reports of any patients in WA developing M. chimaera infection from contaminated HCDs.

The Australian Commission for Safety and Quality in Health Care (ACSQHC) has issued national infection control advice on this issue.

At a meeting of Chief Health Officers from around the country on 15 December 2016, it was agreed that all states and territories that have patients at risk would undertake a patient notification exercise to ensure a nationally-consistent approach to this issue.

In Western Australia, all WA hospitals that perform cardiac bypass surgery have tested all HCDs to determine the presence of M. chimaera. Hospitals that identified contaminated HCDs have implemented risk mitigation strategies recommended by the TGA, the ACSQHC and the Centres for Disease Control and Prevention in the United States. All contaminated HCDs used in WA have either undergone extensive disinfection processes to remove the bacterium, or been replaced with new HCDs. Testing of the HCDs is ongoing at all hospitals and no further positive results have been reported.

Infection risk assessment

Recent information indicates that the infections are almost always associated with surgery involving some form of prosthetic implant e.g. valves or aortic grafts. Patients who have had coronary bypass grafting, transplantation, or other cardiac procedures without any prosthetic implants appear to be at an extremely low risk of NTM infection from HCDs. The time to diagnosis can be up to 5 years following exposure to this organism, although the median time to symptoms in the identified cases from overseas is approximately 18 months.

Although the risk is considered to be very low, estimates of the absolute risk for an individual patient have varied widely. Initially, Public Health England indicated an estimated risk of approximately one case of M. chimaera infection for every 10,000 patients undergoing open heart surgery, although the Swiss patient cohort data estimated the risk to be about 1 in 500 for patients with prosthetic implants.

WA patients at potential risk of exposure include those who have had their cardiac surgery at Fiona Stanley Hospital, Fremantle Hospital, Princess Margaret Hospital, Royal Perth Hospital, the Mount Hospital, and St John of God Hospital Subiaco. The HCDs used at Sir Charles Gairdner Hospital were purchased at an earlier date than other HCDs used in WA and have repeatedly tested negative for M. chimaera over many months.

Patient assessment

Symptoms of M. chimaera infection are non-specific and may include any one or more of the following, occurring for two weeks or more:

  • unexplained fevers
  • night sweats
  • unexplained weight loss
  • increasing shortness of breath
  • joint or muscular pain
  • nausea, vomiting or abdominal pains
  • malaise (note: fevers or night sweats or weight loss should also be present with malaise)
  • pain, redness, heat or pus around the surgical site.

Initial assessment

Patients with a history of cardiac surgery who present with this symptom complex are more likely to have causes other than M. chimaera infection. Before referral and specialised testing for mycobacterial infection, these more common causes need to be considered. Conventional blood cultures should always be performed when patients present with the above symptom complex.

Assessment for mycobacterial infection 

Diagnosis of prosthetic valve endocarditis (PVE) or disseminated infection due to M. chimaera is based on:

  • detailed patient history
  • physical examination – for signs of valvular pathology, splenomegaly and retinal involvement
  • routine blood tests: FBE, biochemistry CRP - disseminated NTM infections should be considered in the symptomatic patient with unexplained anaemia, thrombocytopaenia, pancytopaenia or unexplained elevated liver function tests
  • imaging studies based on signs and symptoms
  • echocardiography including transoesophageal echocardiography
  • biopsy of any tissues as may be implicated with a systemic infection (include request for mycobacterial culture).

It is strongly recommended that an infectious diseases physician or clinical microbiologist be consulted prior to requesting specialised tests for mycobacteria, especially as laboratory capacity to provide such testing is very limited. Such specialised testing includes blood culture for NTM (acid fast bacilli (AFB) blood culture) and bone marrow culture for NTM. When recommended, two MycoF lytic bottles should be collected on separate days.

HCD-associated infections have not included pulmonary infections, and sputum cultures for mycobacteria are not indicated (in the absence of other features of pulmonary disease).

Investigation is not indicated for asymptomatic patients

Only patients who have signs and symptoms consistent with PVE or a disseminated infection syndrome such as pyrexia of unknown origin (PUO) should be investigated. There is no indication to investigate asymptomatic patients for possible systemic NTM infection, including the ordering of AFB cultures. There is no recommended screening laboratory test, culture or imaging modality for the asymptomatic patient. 

Patient management

Management of M. chimaera infections requires an interdisciplinary approach and is best managed and co-ordinated by an infectious diseases physician or clinical microbiologist experienced in the treatment of mycobacterial diseases.

Treatment for NTM infection requires prolonged combination antibiotic therapy based on susceptibility testing. Antibiotics used to treat common bacterial infections are usually not active against M. chimaera. The optimal duration of therapy is unknown, however 12 months is commonly cited. Revision cardiac valve surgery in addition to antibiotic therapy may be required for cure in some cases.

There is no antimicrobial prophylaxis treatment for the potentially exposed patient. In this instance, antimicrobial prophylaxis could promote resistance if subclinical disease is already present. 

Notification of patients with M. chimaera infection

All patient cases of M. chimaera following cardiac surgery are to be notified to the Director, Communicable Disease Control Directorate on 9388 4801 and the Therapeutic Goods Association.

More information

Mycobacterium chimaera in heater-cooler devices – information for clinicians (PDF 173KB)

Mycobacterium chimaera information for GPs (PDF 246KB)