CHEVERLY, Md. — The neonatal intensive care unit at Prince George’s Hospital Center was temporarily shut down Tuesday after the discovery of potentially deadly bacteria in nasal swabs of three infant patients, hospital officials said.

Nine babies were being transferred from the hospital in Cheverly, Maryland, to the NICU at Children’s National Medical Center in Washington “out of an abundance of caution,” said Delores Butler, a spokeswoman for Dimensions Healthcare Systems, a nonprofit entity operating hospitals in Prince George’s County.

Those transfers were expected to be completed by Tuesday night.

Hospital officials emphasized that the babies who tested positive for the pseudomonas bacteria have not shown any symptoms of illness from that infection, which can be mild in healthy individuals but far more serious for those with compromised or immature immune systems.

Dimensions board members were notified by phone Sunday about the presence of what hospital officials are describing as a troubling “cluster” of the bacteria among the NICU patients, according to two individuals with direct knowledge of the phone calls.

The discovery of the bacteria followed two recent deaths in the neonatal unit, said the two people, who spoke on the condition of anonymity because they were not authorized to comment. They also said the bacteria were found in water pipes near the NICU.

Hospital officials said that the cause of the two infant deaths was still being investigated and that so far there was no evidence that the deaths were related to the presence of the bacteria.

“There have been no clear deaths associated with these infections,” said Carnell Cooper, chief medical officer for the hospital center.

He added that neonatal patients suffer from “a number of conditions that put them at risk to die.”

Cooper declined to provide details on the infants’ deaths, which along with the presence of the bacteria, were first reported by WJLA (Channel 7).

He said the hospital routinely swabs the nostrils of infants in the NICU to survey the amount and types of bacteria on their skin. When those tests showed pseudomonas in more than one baby, the hospital notified state health officials, who suggested moving the infants to another hospital.

Hospital officials are now working backward to determine how long the bacteria may have been present in the NICU and how they were introduced.

The hospital stopped admitting neonatal patients Thursday and also stopped using tap water in the intensive care unit at that point, said Dimensions executive vice president Sherry Perkins.

Joan Hebden, a nurse specializing in infection prevention with the University of Maryland Medical School, said the hospital has hired a water company to collect samples and analyze the water to determine the source of the bacteria.

Water enters the hospital through three intakes from a local municipal system that has its own filtration system, she said. Hebden did not say whether the NICU has additional water filtration or uses a separate system for its sensitive patients.

The strain of pseudomonas, she said, does not appear to be resistant to antibiotics. Hebden said there are no signs of any problems with water elsewhere in the hospital building.

All water entering and leaving the facility will be tested several times and decontaminated, if necessary, before the NICU can be reopened, hospital officials said.

“In most cases, there is no single source of contamination,” said Kerri Thom, an infectious-disease physician with the University of Maryland Medical School. “However, in many cases, a water source can be implicated.”

When found in tap water, Pseudomonas aeruginosa, one of the most common strains of pseudomonas, is not harmful to most healthy people, experts said.

But it is a bigger problem in hospitals, where it can be fatal in patients with weakened immune systems, said Chuck Gerba, a microbiology professor at the University of Arizona who has written about pseudomonas.

Patients can become ill from drinking water that contains the bacteria, or from being contaminated by health care workers who wash their hands with such water, he said. Gerba said pseudomonas is “fairly common” in household water faucets, but studies have shown that hospitals that use water filters cut down on pseudomonas infections by 95 percent.

Prince George’s Hospital Center has the only Level 3 NICU in Southern Maryland, according to the hospital’s website. NICUs designated as Level 3 can provide continuous life support for “extremely high-risk newborns and those with complex and critical illnesses,” according to the American Academy of Pediatrics website.