Mycobacterium chimaera is a type of bacterium known as a non-tuberculous mycobacterium (NTM). There is a risk that heater cooler units — medical devices used in cardiac (heart) surgery — may be contaminated with this bacterium. As a result, there is also a small risk that patients exposed to the exhaust from these units in the operating theatre may develop a serious infection, sometimes up to several years after surgery.
A small number of cases of serious Mycobacterium chimaera infection have been reported in several countries. Infection is a recognised possible complication of any surgery, and a small proportion of people who have cardiac surgery (between three and six per cent) will develop an infection of some kind. This may happen shortly after surgery, or many months or even years later.
How the infection can occur#
A possible source of infection in a very small number of people who have open heart surgery is the bacterium Mycobacterium chimaera. It has been found to contaminate the water tanks of a medical device called a heater cooler unit, which is used to regulate body temperature during open heart surgery.
The chance of the bacteria being transferred from the heater cooler unit to a person having heart surgery is extremely low. Fewer than 100 people worldwide are known to have contracted the infection in this way. The risk is reduced further by regularly changing the water in the heater cooler unit tanks and by enhanced disinfection measures.
What is Mycobacterium chimaera?#
Mycobacterium chimaera is a non-tuberculous mycobacterium (NTM). NTM are commonly found in the environment, including in soil and water. They are generally not harmful, although in very rare cases they can cause infection in surgical patients, especially in people with weakened immune systems. They can also cause lung disease if inhaled. These infections may be treated with antibiotics.
Who is at risk?#
People who have had open heart surgery in which an artificial (prosthetic) heart valve or other prosthetic material was inserted are at the highest risk of Mycobacterium chimaera infection.
If you have had this type of heart surgery and you develop any of the following symptoms, contact your doctor or the hospital where the surgery was performed without delay:
- pain, redness, heat or pus around the surgical site
- prolonged or unexplained fever
- night sweats
- unintentional weight loss
- marked fatigue
- increased shortness of breath
- joint or muscle pain
- nausea, vomiting or abdominal pain
If you are scheduled for cardiac surgery#
If you are scheduled for cardiac surgery, the risk of surgical complications, including infections, will be discussed with you as part of the informed consent process. The risk of mycobacterial infection from heater cooler units is considered very low compared with the overall risk of surgical and valve infection.
If you have particular questions about Mycobacterium chimaera infection, or any other type of infection, discuss them with your surgeon during your pre-admission appointments.
What is being done to protect people#
Health services where open heart surgery is performed, together with public health authorities, have been working to further reduce the risk of Mycobacterium chimaera infection. Heater cooler units are tested and monitored, and strict maintenance and hygiene measures continue. Some of the older units thought to be more prone to contamination have already been replaced. Contact your treating health service for further information if needed.
Key points#
- The chance of the bacteria being transferred from the heater cooler unit to a person having heart surgery is extremely low.
- NTM are commonly found in the environment, including in soil and water.
- NTM can also cause lung disease if inhaled.
Sources & further reading
For evidence-based global guidance on this topic, consult authoritative public-health bodies such as the World Health Organization (WHO), CDC, NHS, and ECDC.