October 1997
BOSTON — A strain of fast-moving bacteria killed four infants in as many weeks at one of the most prominent children's hospitals in the country, forcing it to shut down its neonatal intensive care unit (NICU) while health officials tried to determine how the bacteria was spread.
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The 16-bed NICU of Boston Children's Hospital was closed Aug. 29 when it was discovered that a strain of Pseudomonas aeruginosa had invaded the unit and killed four newborns, two within a week of each other. A fifth death caused by Pseudomonas was reported in the same unit in June of 1996, but Children's Hospital epidemiologists still have not identified the strain responsible. The investigation is being conducted by Boston Children's Hospital and Massachusetts Department of Public Health epidemiologists. The Centers for Disease Control and Prevention (CDC) in Atlanta were informed of the situation, but had not been asked to join in the investigation, health officials said.
So far, no evidence has surfaced that would point toward a new, antibiotic-resistant, super strain of P. aeruginosa, but investigators are speculating that the bacteria could have been brought into the unit by either an infected newborn or possibly a hospital employee. There are a whole host of hospital workers that have regular access to the unit at any one time; phlebotomists, respiratory therapists, X-ray technicians and custodians. In tests, one employee was found to have the bacteria on her hands, but it could not be determined if she carried the strain into the unit.
"This is a strain more commonly found in the hospital environment ... person-to-person transmission is rare," said Bela Matyas, MD, medical director of the epidemiology program for the Massachusetts Department of Health. "[Pseudomonas] is not known to survive on a person's skin, but if this turns out to be the case, then we could be dealing with an unusually virulent strain."
While Matyas sees the strain as being unusual, he doesn't necessarily think it could be a new type of super-organism. He believes it might be a strain that has been around for quite a long time, but simply not yet catalogued by scientists since the testing method for identifying these types of organisms is new in the field of epidemiology. However, while the organism itself might be common, the high fatality rate it inflicted on the NICU at Children's Hospital is not, he said.
"Pseudomonas infections don't usually kill the people they infect, and they don't kill at this high rate of speed," said Matyas. "It's impossible to predict how common this strain may now become."
Pseudomonas are a bacterium that grow in moist areas and are found in all hospitals. It can often be carried to humans on vegetables and fruit. For example, it is common in the lettuce used in salads and can also be found in drinking water.
Pseudomonas strains can also be found in nursing homes and some private practice offices, but are not usually thought of as deadly like the strain found at Children's Hospital, said state health officials.
People in good health rarely become sick from it, although it can be dangerous to premature babies, the very old and those with weakened immune systems, such as patients with AIDS. What baffles hospital investigators is that the bacteria is usually susceptible to antibiotics.
"There's no such thing as a bacteria-free environment — especially in hospitals," said William Trick, MD, of the CDC. "There are a number of ways to transmit bacteria in a hospital setting; through aerosol medications, ventilators, catheters, and nurses handling [premature infants] with unwashed hands. These can all play roles in facilitating the spread of bacteria, even in areas that are posted as germ-free environments." Trick said that of the 2 million infectious diseases annually picked up by hospital patients, about 10% can be linked to the P. aeruginosa strain.
The unit, considered one of the best in the country, normally admits 500 to 600 premature infants a year. Twenty to 30 babies, or around 4%, die each year. The unit was moved to a new building in 1987 and up until that time had never suffered any infectious outbreaks of this scale. Hospital officials said the reason why this particular strain appears so lethal is due in part to the population it struck. The 500 premature infants found in the unit are the sickest children in the region. They are frequently connected to ventilators and other equipment that can make it easier for dangerous microbes to enter the body.
"We're seeing this happen in a hospital and not in a private practice because that's where our sickest populations are," said Edward O'Rourke, medical director of infection control at Children's Hospital. "We cannot prevent these events from happening, but we can try to cut them off at the pass, to prevent them from spreading to other people. We'll find out what happened ... but it's going to take time."
An outbreak such as this reminds all physicians and hospital staff of the importance of hand washing and other, basic infection control procedures.
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