Tap Water Contaminates Patients’ Lab Specimens With Mycobacterium porcinum


A hospital’s infection control team, with the help of Wisconsin health officials, traced the source of contaminated patient lab specimens back to tap water in 2 ice machines and 1 water dispenser inside hospital intensive care units (ICU). The water was contaminated withMycobacterium porcinum, a rapidly growing nontuberculous mycobacterium which causes respiratory tract infections, according to today’s Morbidity and Mortality Weekly Report (MMWR), published by the US Centers for Disease Control and Prevention. 

The hospital identified a cluster of 7 isolates that tested positive for M. porcinumfrom January to December 2017. The specimens were obtained from sputum, bronchoalveolar lavages, or bronchial aspirates in the ICU. No clinical infections were reported in association with the isolates. 

“Because M. porcinum is rarely encountered, a concern that these isolates represented laboratory contamination was raised, and the hospital infection prevention team began an internal investigation,” reports MMWR. 

Health investigators with the Wisconsin State Laboratory of Hygiene (WSLH) and the hospital’s infection prevention team looked for possible breaches in infection control and lab processes. They found 4 additional isolates in January 2018. After that, all patient specimens submitted for acid-fast bacteria culture were sent directly to WSLH, which identified 3 additional M. porcinum isolates. This suggested that the specimens weren’t contaminated in the hospital’s lab. By April, a total of 20 isolates had been identified. 

“A retrospective chart review demonstrated that none of the isolates were associated with a clinical infection; other infections accounted for all patients’ illnesses,” MMWR reports.

Investigators knew that M. porcinumis often found in tap water, and that nontuberculous mycobacteria have also been associated with outbreaks in healthcare settings in the past. They also knew that tap water was used during respiratory specimen collection at the hospital. They examined ice machines, water dispensers, and hand washing sinks in the ICU and found M. porcinum isolates in the 2 ice machines and 1 water dispenser.

“Inspection of these machines demonstrated visible debris on internal machine parts and dispenser spouts,” MMWR reports. “Since the installation of new machines and parts in June 2018 and revision of the hospital’s cleaning protocols, no further M. porcinumpatient isolates have been identified. In accordance with a recommendation from the Wisconsin Division of Public Health, staff members at this hospital no longer use tap water when collecting respiratory cultures.”

MMWR concludes that hospital water management programs “should engage clinical partners to ensure safe water use as part of patient care and address maintenance of ice machines and water dispensers within their facilities.”

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