A preterm infant developed severe meningitis and was left with destroyed brain tissue after being fed milk from a contaminated breast pump, say U.S. public health officials.

The Pennsylvania girl was born prematurely, at around 29 weeks. Doctors consider a baby preterm if born before 37 weeks of pregnancy.

The baby showed signs of a severe infection at about three weeks old. Tests showed she had Cronobacter sakazakii growing in her spinal fluid. She developed severe meningitis and was left with profound developmental delays, said Dr. Anna Bowen, a medical epidemiologist with the U.S. Centers for Disease Control in Atlanta.

In Thursday's issue of the agency's weekly report on death and disease, Bowen and federal, county and hospital investigators describe how they traced the likely source of contamination.

The bacterial infection is rare in infants. The CDC typically hears of four to six cases a year.

Infections in infants have repeatedly been linked to powdered infant formula, so that's where the investigation began. But the baby never had formula.

"We went sort of hunting down new avenues looking at all of the food exposures that this infant has had, as well as some environmental exposures and medication exposures, and wound up finding the Cronobacter only in the breast pump used at home as well as the milk samples that had been pumped at home," Bowen said in an interview.

Breastfeeding and pumping encouraged

The researchers also found the same strain in the drain of the kitchen sink in the mother's home.

"This case touched us very deeply and made us question whether women were getting the guidance they needed to pump their milk as safely as possible for their babies," Bowen said. "Breastfeeding is really one of the best things that a mother can do for her baby's health and development and we applaud mothers for pumping when the baby isn't able to directly breastfeed."

The agency's best practices for using breast pumps recommends key steps. These include that:

  • Women wash their hands before handling pumps or pump kits.
  • Immediately chill pumped milk after pumping.
  • Carefully clean the kit as quickly as possible after pumping.
  • Consider using a separate basin since kitchen sinks are easily contaminated and hard to clean thoroughly.
  • Scrub well with soap and a dedicated scrub brush.
  • Air dry thoroughly rather than using kitchen towels that might harbour germs.
  • Store carefully to avoid contamination.

As an extra precaution, particularly for preterm infants or those under two months of age, people can sanitize the equipment in the dishwasher, with boiled water or a commercial sanitizing kit.

1st such infection

"It's fairly common for pumped breast milk to become contaminated and not necessarily with Cronobacter. In fact, this is the first time we've seen an infection of this sort linked to pumped breast milk."

There are many bacteria in human milk even before it is expressed from the breast, said Dr. Sharon Unger, a pediatrician in Toronto and medical director of Ontario's milk bank. Newborns likely acquire bacteria from their mother and they don't cause infection in full-term, healthy infants.

The concern arises when the milk is being fed to a preemie whose immune system has not matured, Unger said. For them, in very rare instances, an infection can occur. 

"For this reason, we have posted detailed instructions and a video on our milk bank website in order to minimize bacteria in milk that is sent to us," Unger said in an email. 

Mothers in the neonatal intensive care unit receive similar instructions.

"Further, this is a reason for always pasteurizing human donor milk and not informally sharing such that we can assure the safety of donor milk. We do not pasteurize mother's milk for her own infant as we want the infant to be colonized with the same bacteria as the mother both by providing her breastmilk and by the infant having skin to skin care." 

Previously, health authorities in Canada and the U.S. have said that breast milk bought online can be contaminated with disease-causing bacteria.

Several other Canadian cities have human milk banks that screen and pasteurize donated milk for preterm and high-risk infants. 

With files from CBC's Amina Zafar