The following Q&A provides information to health care providers who may be caring for patients who have had cardiothoracic surgery and are concerned. The Provincial Infection Control Network (PICNet) led the design of the approach, and the contents of the Q&A.
What is the infection & where did it come from?
Mycobacterium chimaera is a type of bacteria known as nontuberculous mycobacteria (NTM). NTM is commonly found in the environment from sources such as soil and water, including tap water. Transmission is thought to occur via aerosolization of contaminated water from this heater-cooler unit.
Some confirmed cases in Europe and North America have been traced to a specific unit – the LivaNova PLC (formerly Sorin Group Deutschland GmbH) Stӧckert 3T heater-cooler system – which was likely contaminated with M. chimaera during manufacturing.
Who are the patients affected & what are the risks?
Heater-cooler units are routinely used in the operating room to control the patient’s blood temperature during cardiopulmonary bypass which includes the following: valve replacement, or annuloplasty, or cardiac or thoracic aortic graft/prosthetic material, or left ventricular assist device (LVAD), or heart transplant, or lung transplant, or coronary artery bypass graft (CABG). Among these cardiac surgeries involving cardiopulmonary bypass, it appears that CABG (alone) is probably even lower risk for M. chimaera infection compared to the other surgeries. The heater-cooler units are in use in surgical units across BC.
Patients who have had cardiothoracic surgery may have been exposed to contaminated units. However, the presence of an NTM infection in a cardiac patient does not mean that the patient was infected by a contaminated heater-cooler unit. NTMs are ubiquitous in the environment and may cause opportunistic infections amongst immunosuppressed individuals, including those with cardiothoracic surgeries, regardless of exposure to the HCUs. The risk to a patient is very low. NTMs are not transmissible from person to person.
How are potentially infected patients being identified?
To date, a review of surgical site infection records in health care facilities have not detected any cases in BC. Cardiac Services BC’s patient registry and the BC Centre for Disease Control Mycobacteria database were reviewed for potential cases of M. chimaera associated with cardiac surgery and no patients have been identified to be affected . Ongoing surveillance measures are in place.
What is the incubation period for this infection?
Because these NTMs are very slow growing, initial signs and symptoms may be nonspecific. The incubation period for identified M. chimaera cases ranges from three months to five years, with a median of 18 months after the index surgery.
What is the spectrum of illness with this infection?
Initial symptoms may include fatigue, shortness of breath, unexplained weight loss and possibly fever. Ultimate diagnoses related to M. chimaera infection may include prosthetic valve endocarditis, prosthetic vascular graft infection, paravalvular abscess, and pseudo and mycotic aneurysms. Extra-cardiac manifestations have also been reported, including bone infection (osteomyelitis, spondylodiscitis), sternotomy wound infection, mediastinitis, hepatitis, chronic respiratory infections, and bloodstream infection (BSI).
Ocular (panuveitis, multifocal chorioiditis, chorioretinitis) and other embolic and immunologic manifestations (arthritis, bone marrow involvement with cytopenia, cerebral vasculitis, pneumonitis, myocarditis, granulomatous nephritis) have also been described. Splenomegaly is observed in approximately 80 per cent of cases as well as bone marrow involvement with cytopenia.
When should I investigate my patient for M. chimaera infections?
As some of the signs and symptoms are common, it is important to rule out other more likely infectious and non-infectious etiologies before initiating investigations for NTM infection. In some circumstances, largely due to severe illness or when patient follow-up will be complex due to frailty or geographic access, clinicians may consider proceeding to NTM testing without waiting.
Consultation with an infectious disease specialist or medical microbiologist for investigation of possible NTM infection is recommended prior to submission of specimens. Testing of asymptomatic individuals who have undergone cardiothoracic surgery (which included cardiopulmonary bypass) is not warranted based on current evidence.
What are the criteria for M. chimaera testing?
The recommended testing criteria are based on risk exposure and compatible clinical syndromes for patients with symptoms that have appeared or significantly worsened following surgery AND have had their symptoms for ≥ three weeks (i.e., to eliminate self-limited infections such as viral infections):
Criterion 1: Patients must have had cardiothoracic surgery requiring cardiopulmonary bypass starting in January of 2011 onward.
Criterion 2: The nonspecific and varied symptomatology makes distinction of NTM infection from other, more common causes difficult. A compatible syndrome is defined as presence of two or more of the following signs and symptoms lasting for at least three weeks with no other identified etiology:
- Constitutional: recurrent or prolonged fever, fatigue, shortness of breath, weight loss, night sweats
- Cardiac: prosthetic valve endocarditis and/or prosthetic vascular graft infection
- Extracardiac: bone infarction, sternotomy surgical wound infection, mediastinitis, hepatitis, bloodstream infection
- Immunologic/embolic: splenomegaly, ocular, cytopenia
- Infants: febrile episodes and failure to thrive
What are the tests & specimen types for M. chimaera testing?
Consultation with an infectious disease specialist or medical microbiologist for investigation of possible NTM infection is recommended prior to submission of specimens.
How should I treat my patient for M. chimaera infections?
If your patient has confirmed M. chimaera or any other infections identified through the investigations outlined above, the consulting infectious diseases physician will guide treatment plan.