Mycobacterium chimaera Infections After Heart Surgery, Los Angeles County, 2016–2017

In December 2016, a hospital in Los Angeles County, California — "hospital A" — reported two infections with Mycobacterium chimaera in patients who had undergone cardiopulmonary bypass surgery within the previous five years. Both operations had used a Sorin Stöckert 3T heater-cooler unit, a device that heats and cools blood during surgery.

A known hazard

These units had already been linked to M. chimaera outbreaks among heart surgery patients in Europe and the United States. Units contaminated during manufacturing before September 2014 released bacteria-laden aerosols during operations. Hospital A had removed and replaced its units.

M. chimaera, a nontuberculous mycobacterium first described in 2004, is hard to diagnose:

• symptoms can take months or years to appear and are often vague — infections have been diagnosed up to 6 years after surgery;
• the right cultures may not be ordered, and because the bacterium grows slowly, results may come back negative.

In hospitals with confirmed infections, rates among exposed patients ranged from 1 in 100 to 1 in 1,000, about half of infected patients died, and infections were most common in patients who received valve replacements or other implants.

The investigation

In October 2016, CDC recommended that hospitals using these units notify patients exposed during 2012–2016. In December 2016 the Los Angeles County Department of Public Health began an investigation at hospital A to find more cases and put control measures in place:

• about 4,000 patients received letters explaining the possible exposure and urging them to seek care for symptoms such as fatigue, unexplained fever, night sweats, weight loss or wound infection;
• a nurse call center answered questions and referred patients to care;
• clinical staff were notified, and an alert was added to the electronic health records of exposed patients;
• the hospital was told to report cases to the Food and Drug Administration through MedWatch.

What it found

By May 2017, 20 confirmed cases had been identified in patients who had bypass surgery during 2013–2016.

Lessons

Informing and reminding exposed patients to seek care for vague symptoms can be key to diagnosis — especially since later care may happen somewhere other than the hospital where the exposure occurred. Because M. chimaera can take so long to cause illness, hospitals that used the implicated units could consider extra steps for early detection, such as re-notifying patients every year and adding clinician alerts to medical records.

Sources

• Jarashow MC, Terashita D, Balter S, Schwartz B. "Notes from the Field: Mycobacteria chimaera Infections Associated with Heater-Cooler Unit Use During Cardiopulmonary Bypass Surgery — Los Angeles County, 2012–2016," MMWR Vol. 67, Nos. 51–52, CDC; a work of the United States government in the public domain. The report's title reads "Mycobacteria chimaera"; its text, and this page, use Mycobacterium chimaera.