Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. A cluster of four cardiac surgery patients were found to have Mycobacterium abscessus infections on the same floor at the Brigham and Women’s Hospital.

2. Analysis found these infections to be related to the water purification system that inadvertently dechlorinated municipal water before it reached the hospital unit.

Evidence Rating Level: 3 (Average)

Study Rundown:

Mycobacterium abscessus is a rare hospital-acquired pathogen, often linked to contamination of high-humidity or aqueous systems. The current study reported on a cluster of nosocomial M. abscessus infections in four patients following cardiac surgery and the steps taken to investigate the cause and mitigate future risk. These infections occurred at different time periods in different rooms on the same floor. First, whole-genome sequencing results from culture samples confirmed homology between the four infections. After ruling out other potential common contamination sources, environmental cultures were examined and revealed heavy mycobacterial growth in the ice and water machines within the infection cluster’s unit. This was not observed in other similar environmental cultures, such as ice and water machines, showers, or sink faucets in the hospital’s other inpatient buildings. Whole-genome sequencing of these cultures was identical to those isolated from affected patients. Further investigation revealed a water purification system with charcoal filters and an ultraviolet irradiator, which inadvertently removed chlorine from the municipal water source. Thereafter, high-risk patients were switched to sterile water, ice, and water machine maintenance was intensified, and the purification system was decommissioned, resulting in no further cases.

In-Depth [case series]:

The current study described M. abscessus infections in four cardiac surgery patients at the Brigham and Women’s Hospital. Three patients had left ventricular assist devices, and the fourth was immunocompromised. All were men with an average age of 62 years. M. abscessus was cultured from patient samples, including blood, left ventricular assist device driveline infection, wound infection, and other body sites. Despite aggressive antimycobacterial treatments, three out of four patients died. These cases were all found on one inpatient floor. Two out of the 14 water specimens from sink and shower faucets showed a low level of mycobacteria, while water specimens from the floor’s ice and water machines showed high levels of mycobacterial growth. Further speciation and sequencing found M. abscessus, along with other Mycobacterium species. The genetic samples obtained from the ice and water machines were found through whole-genome sequencing to match closely with the samples from the case patients. Inspection of these machines found large amounts of biofilm formation, despite adherence to manufacturer-instructed maintenance. Chlorine was undetectable in the affected ice and water machines. Plumbing infrastructure analysis of the cluster tower identified a commercial water purification specific to the affected ice and water machine that included a carbon filter and an ultraviolet irradiator, resulting in a substantial reduction in chlorine levels compared to a municipal water source. The study demonstrated the unintended consequences of water-improving systems and the importance of regularly monitoring hospitals’ water systems.

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