In early October, three babies died after contracting a waterborne bacterial infection at a hospital in Danville, Pennsylvania. After more than a month of investigating, the hospital said Friday that it finally discovered the cause: breast milk that had been contaminated by hospital equipment.

The milk sickened eight babies in a neonatal intensive care unit, killing three, Geisinger Medical Center said. Infection control specialists explained that the equipment used to measure and administer donor breast milk was tainted with Pseudomonas bacterium, a hospital spokesperson confirmed to CBS News.

Hospital officials stressed the milk itself was not the source. Since the discovery, the hospital said it has switched to using single-use equipment.

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"We have had no new cases of infants becoming ill from Pseudomonas in the NICU since making this change," Dr. Edward Hartle, Geisinger's executive vice president and chief medical officer, said in a statement.

The hospital said some premature newborns and expectant mothers are being sent to other facilities while it works with state health officials to resume normal operations.

"We would like to extend our sincere apologies to the families who have been affected by this incident. We know that the public holds us to the highest standards, and we will continue to strive to live up to those expectations as we have throughout our history, constantly improving on what we do and how we do it," Hartle said.

The bacteria are common and often harmless, but can cause disease in "very fragile patients," Dr. Frank Maffei, the hospital's chair of pediatrics, said at a news conference when the incident first occurred.

The deaths, he said, "may have been a result of the infection complicating an already vulnerable state."

The parents of one of the newborns who died filed a lawsuit against the hospital last month for its alleged failure to protect their son from the lethal infection, which had already killed two other babies.

"A key aspect is to determine whether this was an ongoing problem there. We now have additional work to determine whether these infection control procedures were deficient for a period of time longer than Geisinger's statement suggests," the family's attorney, Matt Casey, told The Associated Press.