Enlarge / Part of the Brigham and Women's Hospital in Boston on Dec. 16, 2021. (credit: Getty | John Tlumacki)

Water purification systems installed in two ice machines in a Boston hospital were supposed to make the water taste and smell better for patients on a surgery floor—but it ended up killing three of them, an investigation found.

The purification systems inadvertently stripped chlorine from the municipal tap water, allowing bacteria normally found at low levels to flourish and form biofilms inside the machines. This led to infections in four vulnerable cardiac-surgery patients who had prolonged stays on the hospital floor. Three of them died of their infections.

Researchers detailed the case cluster and ensuing investigation in a study published Monday in the Annals of Internal Medicine.

Enlarge / The Abbott manufacturing facility in Sturgis, Michigan, on May 13, 2022. (credit: Getty | Jeff Kowalsky)

The Department of Justice's consumer-protection branch has opened a criminal investigation into the conduct of Abbott Laboratories, one of the country's largest formula makers at the center of a contamination scandal and ongoing nationwide shortage.

The existence of the investigation was first reported by The Wall Street Journal. Though the DOJ is not commenting on it, a spokesperson for Abbott said the department has informed them of the investigation and that the company is "cooperating fully."

Federal regulators last year found numerous violations and "egregiously unsanitary" conditions at Abbott's Sturgis, Michigan, plant, the largest formula factory in the country. The regulators previously received reports that at least four babies who drank formula made at that facility fell ill with dangerous infections of the bacterium Cronobacter sakazakii, which had also been detected in the plant. Two of the infants died.