Eleven babies in the intensive care unit were exposed to the tainted feeding drips, and one was still fighting for its life, according to officials at the University Medical Centre of the Johannes Gutenberg University.
Clinic head Dr. Norbert Pfeiffer said the critically ill baby was not expected to survive, but four other infants were now in stable condition.
“I'm deeply shocked,” Pfeiffer said. “We are all very distraught and upset and our sympathies goes out to the parents and families.”
Senior public prosecutor Klaus-Peter Mieth said on Monday the deadly infections were caused by dirty tubing used for feeding the babies.
“The tubes are the only place on the machines that the workers touch directly and could therefore add bacteria,” Mieth said.
His office is now investigating on suspicion of negligent manslaughter and negligent bodily harm in the case.
“Once we've isolated the germs, then we will also have a chance at catching the actual cause,” Mieth said, but added that it remains unclear whether the contamination was the cause of death to the two infants, who were both already critically ill before they were exposed.
The clinic, however, believes it may be possible the bacteria found its way into the infusions in the hospital pharmacy.
Head of the Rhineland-Palatinate state office of criminal investigation's biology department Rainer Wensel said the room used to prepare the solutions was held to the highest standards of hygiene. Preparation equipment has been seized for further investigation.
The two infants who died, a two-month-old and an eight-month-old, were being treated in the intensive care unit when they received the drip, prepared by the hospital pharmacy from different components from separate producers.
By Saturday morning their health had rapidly deteriorated, at which point doctors gave antibiotics to all of the other babies possibly exposed.
Police and state prosecutors in the state of Rhineland-Palatinate conducted autopsies on both of the babies in Mainz, confirming without a doubt that they had been exposed to the bacteria.
Meanwhile the director of the university medical centre's pharmacy Irene Krämer said that the infusions were prepared individually for each baby, with more than 90,000 problem-free drips over the past 10 years.
But in these cases human error could not be ruled out, she said, because during the preparation of the drips workers changed their gloves about 30 minutes into the process.