The M. chimaera How-to Guide

A few cases at a time, the M. chimaera outbreak associated with heater cooler units continues to grow. For reasons unclear to me, the response from CDC and FDA to this train wreck in slow motion has been underwhelming. We continue to field calls from hospitals struggling to deal with an approach to the outbreak. On today’s IDSA list-serv (IDea Exchange) Dr. Luther Rhodes wrote: “The silence is deafening. I call on those physicians with hands on experience in evaluating post open heart patients referred to ID for evaluation of concerns, signs or symptoms of possible NTM infection to speak up loudly and clearly. Lessons learned, protocols developed, evaluation and testing tools learned dealing with large scale regional patient notification should in my opinion be shared…”

We have posted several times on this topic, but I thought it might be useful to summarize how a hospital could approach this problem in a single post. To view older posts, type chimaera in the search box in the top right hand corner of your display.

Step 1: Determination of risk
Whether you have seen a case or not, the first question is whether your hospital has used the LivaNova Sorin T3 heater cooler unit (HCU) in the last six years. If the answer is no, there is no immediate action you need to take. If yes, then the investigation begins, as you must assume the units are contaminated, regardless of the manufacturing date.

Step 2: Risk mitigation
If you are currently using the LivaNova (Sorin) T3 unit, the most important risk mitigation strategy is to get the units out of the operating room. The molecular epidemiology clearly points to contamination of the HCUs at the manufacturing facility, which allows the units to produce an infectious bioaerosol that contaminates the operative field. Separation of this bioaerosol from the operative field is the key to eliminating the risk. Why the FDA won’t clearly state this is very puzzling.

At the University of Iowa Hospitals and Clinics our engineers were able to quickly (within a few days) devise a solution by creating a 6” x 6” hole (see photos) through the operating room wall on the semi-restricted side of the room. The area identified for creation of this portal was determined by hose access to the OR table with minimal interference with staff and equipment; access to power; and the ability to leave proper corridor width per life safety code. Testing demonstrated that positive pressure was able to be maintained in the OR after creation of the portal. The portal itself with a sliding door was constructed of Corian in some cases and stainless steel in others. A hose protection mat was placed in the ORs to protect the HCU hoses and to provide a ramp effect for equipment to be relocated as needed during the cases. One advantage of the T3 HCU is that remotes can be purchased that allow the perfusionist in the OR to control the HCU located outside of the room. Once the HCUs were moved out of the OR, we demonstrated no difficulty with appropriate heating or cooling. Remember, given the long incubation and detection period of these infections (maximum 6 years to date), if you do not eliminate the risk now, you will likely be chasing cases for many years with no end in sight.

We do not believe that culturing HCUs for M. chimaera is helpful. Most laboratories are not adept at performing environmental cultures for mycobacteria, so the negative predictive value of cultures in this setting is poor. In other words, if cultures are negative, you cannot assume that your machines are not contaminated. Moreover, even when cultures are performed in expert labs, the culture results for any given HCU are not consistent over time; they may be negative at first sampling, then positive on subsequent samples, or vice versa. And it has yet to be demonstrated that once a HCU has tested positive it can be successfully decontaminated, which is an additional reason that we believe that elimination of risk requires removal of the HCUs from the OR.

Follow manufacturer’s recommendations for cleaning and disinfection of HCUs.

Step 3: Case identification and notification
  1. Develop a line list of potentially exposed patients by determining exposure to HCUs over the past 6 years. At our hospital, we found that the easiest way to do this was to identify whether a perfusionist was assigned to the operative case as identified via billing records. It is important to note that you will need to include off pump cardiac cases, since the HCU is typically on “stand by” status, turned on and running in the OR, even if the patient is not on cardiopulmonary bypass. Also, cardiopulmonary bypass is not restricted to cardiac cases; some lung and liver transplants are performed with cardiopulmonary bypass.
  2. Notify potentially exposed patients. We began by sending a letter, explaining the problem and asked patients to call a toll free number to speak with a nurse who did a symptom screen on the phone. Patient who screened positive, were advised to see their local physician or to come to a clinic that we set up for evaluation. A letter to physicians was included with the patient letter and patients were instructed to take the letter to their physician. Patients who did not call in response to the letter were contacted by phone and screened. Our marketing and communications group was very helpful in developing patient materials. They also prepared press releases and established a webpage on the hospital’s website with information for patients and healthcare providers. It’s important to note that patients who are asymptomatic presently will still be at risk for development of infection for several years, so they need to be instructed to seek medical attention should they develop symptoms in the future. The patients at highest risk are those with implants (e.g., cardiac valves, vascular prostheses, ventricular assist devices), though a few cases have been reported in patients without implants.
  3. Notify referring providers and internal physicians who may end up seeing infected patients. We sent letters explaining the infection to all referring providers and broadcast emails to our providers internally. It’s important for providers to think about this infection when they evaluate potentially exposed patients with culture-negative endocarditis, fever of unknown origin, unexplained weight loss, or unexplained granulomatous inflammatory processes, including sarcoidosis. Obviously it’s important for your infectious diseases physicians to be made aware, but other physicians may be involved with cases as well. One of our cases was simultaneously being evaluated by a hematologist, a hepatologist, and an ophthalmologist for a disseminated granulomatous process. Once you have developed your list of potentially exposed patients, you can run it against a list of patients with the aforementioned diagnoses, and further review any patients who appear on both lists.
  4. Ask your lab to produce a list of patients who had MAC isolated from blood, bone marrow or wounds in the last 6 years. Run this list against your list of potentially exposed patients to identify any matches for further review.
  5. Any patient with a consistent syndrome should have 2-3 mycobacterial blood cultures obtained. If suspicion is high and mycobacterial blood cultures are negative, consider obtaining bone marrow biopsy for histopathology and culture.
  6. If mycobacterial cultures grow MAC, depending on your lab’s capabilities, you may need to send the isolates to a reference lab for species identification.
  7. Report M. chimaera cases to the FDA via MedWatch.
Given that the implicated heater cooler unit is the predominant brand, many hospitals will be embarking on an investigation, so hopefully they will find this information of value.

Useful publications:


  1. Can someone comment on the sensitivity of AFB blood cultures in this situation, and the rationale for 2 per patient? I was told that an institution was ordering up to 4 per patient, but if 1 was positive, all 4 were positive. We are concerned with having enough lab capacity, even if we do just 2 per patient.
    Thanks for all the useful info.

  2. It's not the hcu it's the water. Every one of the reporting hospitals are "green" hospitals. All leed awarded. The FDA knows this and continues to blame the hcu. I have the admission of this in writing from one of the hospial that did the research funded by FDA!

  3. It's not the hcu it's the water. Every one of the reporting hospitals are "green" hospitals. All leed awarded. The FDA knows this and continues to blame the hcu. I have the admission of this in writing from one of the hospial that did the research funded by FDA!


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