Correction: Due to incorrect information provided by hospital officials,earlier versions of this article misstated how many infants were impacted by the pseudomonas outbreak. In August, three of nine infants transferred from the NICU had the bacteria present in their systems, but none showed symptoms of infection. During the second outbreak, in November, two of six babies transferred from the NICU had the bacteria in their systems; one of those showed infection symptoms.

(Hamil R. Harris/The Washington Post)

The neonatal intensive-care unit (NICU) at Prince George’s Hospital Center will reopen Monday, officials said, four months after federal infectious-disease experts were called to investigate the outbreak of a potentially deadly bacteria.

The unit was cleared after the Centers for Disease Control and Prevention issued a final report reaffirming that the pseudomonas germ — a common waterborne bacteria — originated in the Cheverly hospital’s plumbing system, and the hospital completed significant improvements to that system.

Of the 15 infants who were transferred out of the hospital’s NICU in August, when the bacteria first appeared in patients, and in November, when the germ reemerged, all but one is now at home, said Sherry Perkins, chief operating officer of Dimensions Healthcare Systems, the non­profit organization that runs the county hospital.

The other baby was not affected by the bacteria but has other health issues and remains hospitalized.

The hospital has invested more than $500,000 in a new water-treatment system to clean and regularly flush its pipes. It also has implemented more-rigid protocols and oversight of ­infection-control procedures for hand washing, bacteria surveillance and water testing.

“Currently, we have had no bacteria in the water system,” Perkins said in an interview. “I feel confident that the water-treatment plan will make us among the safest NICUs in the country.”

The NICU first closed in August, after cultures derived from the nasal swabs of infant patients revealed the notoriously resistant pseudomonas germ.

Nine infants were moved to Children’s National Medical Center in the District. Three had the bacteria in their systems, although none showed symptoms of pseudomonas infection, which can be fatal for premature newborns with underdeveloped immune systems.

Testing revealed pseudomonas in NICU sinks and traced its origin to the water system. Working with experts from the University of Maryland School of Medicine, hospital officials replaced the sinks, chlorinated the system and installed filters.

Less than three months later, the bacteria was back. Six more babies were transferred out. Two had the bacteria in their systems, and one of those two showed symptoms of infection.

CDC experts then broadened their search for other sources of the bacteria, checking NICU equipment, health-care workers and visitors to the unit, as well as the areas around sinks and breast-milk pumps used by mothers. No other source was found, Perkins said.

The hospital will continue to transfer its most vulnerable patients — babies born prematurely at 28 weeks or less — to Children’s Hospital as a precaution.

During the investigation, epidemiologists also reviewed the deaths of seven babies in the year before the germ was detected in the NICU. They determined that five had died of causes unrelated to pseudomonas but that the bacteria probably had contributed to the deaths of the other two.

However, experts could be not be certain. Perkins noted that in both cases the babies were “extremely premature,” had many complications and weighed under one pound.

Perkins said the hospital has toughened its standards and retrained staff to try to stave off transmission and future outbreaks.

“It remains a risk in any NICU,” Perkins said. “There is probably more of this in other NICUs than is reported, because it’s a bacteria that is not typically surveilled.”