Water purification systems installed in two ice machines at a Boston hospital were supposed to improve the taste and smell of water for patients in an operating room, but it ended up killing three, according to a survey.
Purification systems inadvertently removed chlorine from municipal tap water, allowing bacteria normally present at low levels to grow and form biofilms inside machines. This led to infections in four vulnerable heart surgery patients who spent extended stays on the hospital floor. Three of them died of their infections.
Researchers detailed the cluster of cases and subsequent investigation in a study published Monday in the Annals of Internal Medicine.
“Our cluster demonstrates the risk of unintended consequences associated with systems designed to improve hospital water,” concluded the researchers, led by Michael Klompas, who works at the hospital and is a professor in Harvard’s Department of Population Medicine.
Common source
Identifying the cluster and the culprit required significant research; all four cases occurred sporadically between March 2017 and October 2018 at Brigham and Women’s Hospital in Boston. And it wasn’t immediately obvious that they were related.
Doctors became suspicious after taking note of three cases in 2018, all of which had invasive effects Mycobacterium abscessus infections. Mr. Abscess infections are rare, but have been known to be associated with health care – called nosocomial infections – which suggest a common source of infection somewhere in the hospital. This led researchers to search hospital records dating back to 2015 for other possibly related cases. It was then that they identified the fourth case, which occurred in 2017.
Whole genome sequencing of clinical isolates from the four identified cases revealed near-perfect matches of their Mr. Abscess isolated. The genomes of the bacterial isolates had only one to three different point mutations among them; less than 20 suggest an epidemiological link. So the researchers set to work trying to find a common source.
Of the four cases, only three were operated on in the hospital, and they were performed in different operating rooms, with different cardiopulmonary bypass heating-cooling devices, which help control a patient’s temperature. during surgery. Only one patient required hemodialysis, ruling this out as a common source. The researchers also ruled out mechanical ventilation as a source. Although the patients were all on the same cardiac surgery floor of the hospital and each occupied several rooms during their stay, there was only one common room for two of the four patients.
The most obvious similarity between the patients’ stays was that they were all extended. While the average length of stay for similar patients on the cardiac surgery floor was just over two weeks, all four patients had stays between 42 days and 131 days before their Mr. Abscess have been identified. And nurses anecdotally noted that patients seemed to consume more ice cream than others.
pure and deadly
Mr. Abscess is a water-loving bacteria known to be present at low levels in tap water, which is not sterile. So the researchers turned to the hospital’s water sources, examining sinks, showers, and ice and water machines on the floor. Samples from two of the 14 floor-standing sinks and showers showed low levels of Mycobacteria contamination, between 10 and 50 colony forming units per millilitre. But samples from both ice and water machines were heavily contaminated, between 2,000 and 8,000 colony-forming units per milliliter. And from these samples, the researchers were able to fish out genetic sequences unique to the Mr. Abscess isolates that had infected the patients, strongly suggesting that this was the common source.
Although hospital records indicated that the machines had been maintained and cleaned according to the manufacturer’s instructions, the researchers noted bacterial biofilms visible on the internal components of the machines.
Alarmed by the discovery, researchers began inspecting sinks, showers, and ice and water machines in other areas of the hospital, but nothing else had levels of bacterial contamination as high as both machines on the cardiac surgery floor. When they checked the chlorine levels, it made more sense. Chlorine levels were within acceptable ranges for all samples except the two machines.
On closer inspection, the researchers noted that both machines had been fitted with commercial water purification systems that included a 5.0 micron carbon filter (designed to improve taste and remove odors) and a unit. ultraviolet disinfection. Charcoal filters and ultraviolet light are known to reduce chlorine levels. Sampling of the inlet and outlet pipes confirmed that the purification system was eliminating the acceptable inlet chlorine concentration of 2.5 mg/L to 0 mg/L in the outlet.
The ice machines were removed from service in October 2018 and no other Mr. Abscess the infections were subsequently identified.
“Our experience suggests the potential harm of well-intentioned measures designed to improve water quality in healthcare facilities,” the researchers wrote in their study. They described various strategies to help prevent such infections in the future, including switching to sterile or distilled water for patient care, regular sampling, and chlorine monitoring. “Hospitals should be particularly alert to the threat of waterborne infections,” they wrote.