Chimeric Outbreak: Low Risk and Indolent but Nonetheless Deadly

To me one of the more underappreciated forms in which an outbreak can take hold is through contaminated medical equipment. There are several unique aspects of these types of outbreaks I believe makes them particularly difficult to detect and control. First, is the fact that the individuals getting infected are accessing the healthcare system for some reason that may mask the signs and symptoms of infection. These patients can also be at higher risk for ordinarily acquired infections making it less likely that someone would attribute their infection to a specific medical procedure and when infection occurs in these patients, it may be more difficult to treat because of coexisting conditions or, because of the nature of exposure, a deep-seated invasive location. Another factor is that the dose a patient may be exposed to may be small enough that a clinical latency period may occur before exposure and onset of symptoms, making linkage difficult. Indeed some exposures may not result in infection at all. Finally, these infections may not necessarily be clustered geographically and disparate locations may take a while to be knitted together delaying recognition of the outbreak. 

This was all very apparent in the deadly Exserohilum steroid contamination meningitis outbreak and is also apparent in the Mycobacterium chimaera outbreak linked to contamination of heater-cooler units used in cardiac surgery. This outbreak involves at least 79 patients, 17 of whom have died -- a fairly high fatality rate.

Mycobacterium chimaera, a non-tuberculous mycobacterium (NTM), is an indolent slow growing pathogen that can be difficult to diagnose. In this outbreak devices were contaminated during manufacture (in a very large manner) and, because of the fact that the majority of cardiac surgeries in the US use this type of machine, the breadth of exposure is large. However, the complicating factor is that despite exposure to this particular organism the risk of infection is low and symptoms can be non-specific. CDC advises hospitals should consider notifying patients who had exposure to this device after January 1, 2012. Some facilities have notified patients, others have not given the nuances (including the medicolegal implications) of this low risk exposure. A recent piece in the Tribune Review details one patient's experience with his possible exposure and subsequent symptoms.

When people think of outbreaks, it is often in the setting of explosive case counts and calamity. However, medical device outbreaks -- which can carry high fatality rates --  are an important species of outbreaks that are no less impactful or disruptive. Like the two-headed Greek monster that the bacteria is named after, this outbreak possesses a dual nature: both indolent/low-risk but but potentially deadly.