A bacterial infection killed three patients at Brigham and Women’s. Here’s how it got in.
The infectious disease clinician working closely with the cardiac surgery department had an inkling something was off. It was 2018, and she mentioned to colleagues at Brigham and Women’s Hospital the unusual occurrence of a suspicious bacteria, which had popped up several times in the last year and a half. The rare bacteria, Mycobacterium abscessus, can sometimes cause hospital-acquired infections, often from contaminated water. But the number of times hospitalized patients had tested positive for it struck her as unusual.
What followed was a deep dive into infection control that ultimately identified four patients who had been infected with the same strain of M abscessus. Despite efforts to treat the infections, three of the four patients died.
Ultimately the hospital discovered the culprit: a water purification system feeding an ice and water machine on the cardiac unit.
The who-done-it analysis of where the bacteria originated, and the lessons that followed for the hospital about infection control, have been highlighted in a study published by Brigham clinicians on Monday in the Annals of Internal Medicine. The piece lays out the detective work involved in finding a potentially deadly pathogen, and shares critical insight into hospital protocols that researchers hope other facilities will take to heart.
“Every health care facility in the world will have a potential [encounter] with hospital acquired infections,” said Dr. Michael Klompas, an infectious disease physician and hospital epidemiologist at Brigham and Women’s, who led the investigation. “It’s not a unique problem to us. If we pretend it doesn’t exist, we will never be as successful as we can be if we confront these head on.”
Infections disease expert Dr. Todd Ellerin applauded what he described as an intricate, epidemiologic investigation, saying it was unusual for a system to find the source of such outbreaks.
“There is a lot of sleuthing,” said Ellerin, interim chief of medicine and head of infectious diseases at South Shore Health. Ellerin was not part of the investigation, though South Shore is clinically affiliated with the Brigham in several specialties. “The Brigham had to be like Sherlock Holmes.”
Massachusetts hospitals have dealt with several water-born bacterial pathogens in recent years. In 2020, Brigham and Women’s saw a number of infections and three patient deaths from the bacteria Burkholderia cepacia, after patients were contaminated from a type of life support known as extracorporeal membrane oxygenation, which oxygenates a person’s blood outside of their body. In December, Franciscan Children’s hospital had 36 children test positive for the same bacteria; officials suspected that it originated from the tap water.
M abscessus is rare for hospitals to see, with outbreaks often associated with water systems such as heater-cooler devices used for patients undergoing cardiac bypass, and hospital plumbing systems. Though usually of little threat to healthy individuals, infections can be problematic for vulnerable patients, and require large quantities of antibiotics to treat, Ellerin said.
In June 2018, Brigham’s infection control department was alerted to three cardiac surgery patients who developed an invasive infection from the bacteria. Two of the patients had surgically implanted heart pumps known as left ventricular assist devices. Another was a cardiac surgery patient who was immunocompromised.
Klompas said one of the initial challenges was recognizing something was even going on, given the small number of cases with many months in between.
“We get these alerts from various clinicians on a regular basis, and often investigate and find nothing,” Klompas said. “But this we looked at, and said this is unusual, and dove deeper.”
But were there other patients? The hospital searched its own microbiology database going back to 2015, looking for patients at the hospital for a given stretch of time who had a culture that tested positive for the bacteria. That search unveiled a fourth infected patient, also with a left ventricular assist device.
The key question: was there was a central source inside the hospital? All four men, over the age of 50, had been admitted to the cardiac surgery intensive care unit and a stepdown unit, located on a single floor of the hospital, each very ill and hospitalized for a period of weeks to months.
It wasn’t immediately clear what else the patients had in common. Three of the four had surgery at the Brigham, but all in different operating rooms with different devices, and the infection had shown up weeks after their cardiac surgeries. The patients had occupied multiple and largely different rooms. Three of the four had been intubated for long periods of time. However for two of those patients, there were months between when they were on a ventilator and when the bacteria showed up, leading officials to conclude the ventilators likely weren’t the collective source.
But bacteria carries a genetic fingerprint, which would tell the hospital if the patients had been infected with the same strain — and from the same source. Doing such sequencing required help from a research lab at Harvard’s school of public health, which has the capabilities necessary to run tests on such an unusual bacteria.
Most strains are unrelated, and investigations stop there. But in this case, the genetic strains were near perfect matches.
The hospital took cultures from sinks and showers of each of the rooms occupied by patients, but mycobacteria levels were nonexistent or too low, ruling it out as a likely source. But experts did find high levels of mycobacteria from ice and water machine samples on the cardiac surgery intensive care unit and stepdown unit. DNA extracted from the machine samples was an exact match to a gene in the patient outbreak.
Records showed the machines had been cleaned and maintained properly. But further testing unveiled that chlorine levels in the problematic units were undetectable, due to a commercial water purification system the hospital had installed in the plumbing lines leading to these units. The filter included a carbon filter and an ultraviolet irradiation unit, both of which decrease chlorine concentrations. The system was designed to improve the taste, odor, and purity of the water, but allowed the bacteria, normally killed off by chlorine, to proliferate.
“You’d not be surprised if other hospitals and health systems have similar water systems in place, put in with the best of intentions,” Klompas said. “You’d think putting a filter in would make the water better. Low and behold, it has unintended consequences. That was the reason for publication.”
According to the study, mycobacteria likely originated from municipal water, which often have low concentrations of the bacteria. Experts suspect that the infected patients may have been particularly prone to infection, given their long lengths of stay. Nurses noted that these patients in particular consumed large amounts of ice.
Beyond removing the problematic ice and water machines and the purification system, the hospital changed how and how frequently it cleaned and maintained its ice and water machines.
The hospital also now uses sterile, distilled or filtered water for both drinking and patient care for its most vulnerable patients.
Tap water “is fine for you and me and whoever is healthy. Our immune systems can take care of it. But if you are vulnerable, you might not be able to,” Klompas said.
Ellerin, of South Shore Health, said there are lessons for other health systems about the need for more comprehensive hospital surveillance of its water systems. The study is also a critical reminder of the importance of reducing exposure of a hospital’s most vulnerable patients to tap water.
No additional cases of hospital-acquired M abscessus had occurred through September 2022.
Klompas said the outbreak is a warning sign that the national standards of monitoring water inside a hospital — usually focused on legionnaire’s infections — might not be stringent enough.
“Turns out that things good enough to get rid of legionella might not be good enough to get rid of mycobacteria,” Klompas said. “This is a further [area of focus] for federal regulars…to reduce risk of mycobacteria.”
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