Disease detectives solve outbreak of hospital-acquired infections

By Joe Kuttenkuler

RICHMOND, Va. – Epidemiologists and laboratory experts led by a researcher now at Virginia Commonwealth University recently used genetic fingerprinting and microbiology testing to identify bacteria that were the cause of more than two dozen hospital-acquired infections. The disease detectives, as they sometimes are called, traced the bacteria to intravenous bags of pain medication.

The diligent investigation, facilitated by its high-tech laboratory testing, is detailed in the current issue of the New England Journal of Medicine.

"Hospital-acquired infections are not uncommon, but it was unusual to see so many infections of this particular type in an isolated area," said Belinda Ostrowsky, M.D., M.P.H., assistant professor of internal medicine and associate hospital epidemiologist at the VCU Health System since September 2000.

"Based on the preliminary information we had gathered, there were several possible causes for the outbreak," she said. "We needed to run the investigation step by step to make sure we didn’t miss any potential causes."

Ostrowsky was working as an epidemiology intelligence service officer for the Centers for Disease Control in 1999 when the infection outbreak occurred at an unidentified U.S. hospital. She was named to head a team of investigators charged with determining the cause and halting it. The case involved 26 patients who had contracted blood stream infections while staying in the hospital’s surgical intensive care unit between June 1998 and March 1999.

Investigators began by comparing infected patients to non-infected ones. The overriding similarity among the infected patients proved to be the sedative fentanyl – a narcotic used for pain control that is 80 times more potent than morphine.

After determining there were no similar reactions from fentanyl elsewhere in the hospital or the country, Ostrowsky and her colleagues tracked the drug from its delivery to the hospital until it reached the ICU.

"Cultures of unopened fentanyl proved to be sterile. We watched many nurses administer the drug – nothing was improper. Then we found something interesting," said Ostrowsky.

Investigators analyzed two bags of fentanyl taken from hospitalized patients who were showing symptoms of this type of blood stream infection. Using pulse-field electrophoresis, a molecular test used to genetically fingerprint bacteria, Ostrowsky learned bacteria were present in the bags that were identical to bacteria that had been cultured from the infected patients.

The investigators pressed forward, reviewing medical records to identify the health care workers who had been in contact with each patient. Narrowing the field from more than 200, the team zeroed in on five respiratory therapists. Based on signatures from the infected patients’ charts, one among the five had cared for more patients than any other. According to witnesses, the worker also had been seen tampering with some of the bags of fentanyl.

At the request of hospital officials, the respiratory therapist submitted to drug testing. Using hair samples, lab technicians tested for chemicals and found fentanyl in the worker’s hair sample. While no bacteria was ever found on the respiratory therapist, investigators believe it could have been introduced to patients through contaminated needles or through fluid used to replace the fentanyl the worker had removed from the bags.

"Proving the same bacteria was in the patients and the bags of fentanyl was one of the big keys to solving this case," Ostrowsky said. "It gave us the microbiology and molecular evidence, and then the hair testing corroborated our epidemiology that the health care worker was involved."

Once the worker was terminated, the infections stopped.

"This case illustrates how thorough public health investigation, combined with high-tech laboratory testing, can identify the cause of a problem and stop further infections. Patient safety is something we take very seriously," Ostrowsky said.

Each year, about 2 million people contract a hospital-acquired infection, and nearly 90,000 die as a result of the infection, according to the Centers for Disease Control.