"These are very, very sick babies to begin with. (An infection) can increase their chance of dying," Mascola said.
On Friday, the hospital shuttered the pediatrics intensive care ward after discovering the bacterium had infected an infant and a toddler there, Dr. Rosalio Lopez, the hospital's chief medical officer, said in a statement.
Both units will remain closed until the hospital feels they're safe again, Lopez said. Any critically ill babies born at the hospital now are being taken to a special isolation area to be stabilized before being transferred to other hospitals, officials said.
Officials say they've identified the source of the outbreak - a medical instrument called a laryngoscope blade used to look at an infant's larynx that may have not been properly cleaned. Officials don't believe there's a danger to other babies, Lopez said.
Though common, the germ is particularly virulent in those with weak immune systems such as newborns who are premature or critically ill and become resistant to antibiotics.
Babies born before 27 weeks of gestation and weighing less than 2 pounds already have a 40 percent to 50 percent chance of dying from other causes, said Dr. Leandro Cordero, director of the newborn intensive care unit at Ohio State University Medical Center. His hospital had an outbreak a decade ago that sickened about 10 infants, most of whom died.
That mortality rate can rise to 70 percent to 80 percent with a P. aeruginosa infection, he said.
Since Nov. 30, 33 patients have been treated in White Memorial's neonatal unit. Of the five babies who were infected, three died, Lopez said, but only one death appears to have been caused by the infection. Eighteen babies showed no signs of the bacterium. The remaining 10 had colonies of P. aeruginosa in their noses or rectums but no signs of infection.
Thirteen babies remain in the neonatal intensive care unit, Lopez said. The 28-bed unit is in a specialty care tower that opened in April.
Hospital officials said they are seeking outside reviews of all deaths in the neonatal unit since Nov. 30.
The hospital is working with county, state and federal health officials to investigate the outbreak, Lopez said. The hospital also is reviewing and strengthening its policies for controlling infections.