By Stephanie Stahl

DANVILLE, Pa. (CBS) — The investigation continues into the deaths of three infants at a hospital in central Pennsylvania. The Geisinger Medical Center had a problem with a bacteria that the CDC says can be spread on the hands of health care workers or by equipment that gets contaminated and is not properly cleaned.

Eight premature babies — already vulnerable and fragile — contracted a waterborne bacterial infection at the medical center. Three of them died.

“We’re building this shell around the patients to keep them safe and at what point did that break down? And that is what we are still trying to identify,” Geisinger Director of Infection Prevention Dr. Mark Shelly said.

Doctors say it’s a common bacteria called pseudomonas, found in liquids, but only a few types can lead to infection.

“It’s really too soon to say exactly where the organism is coming from, but what we have, the info we have so far suggests it’s some place outside of the NICU,” Shelly said.

All of the babies infected were born under 27 weeks. Four of them have recovered and doctors say they’re now in good health.

One is still receiving treatment.

“Our Neonatal Unit has never seen a situation involving infections like this,” Geisinger Chair of Pediatrics Dr. Frank Maffei said.

The hospital first became aware of an unusual infection in early August.

Officials admit the investigation may never find the cause, but they’ll continue to perform extra cleanings and change some procedures.

Expectant mothers who could deliver prematurely are being told to go elsewhere for now.

Stephanie Stahl