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Healthcare Infection Prevention: HCV outbreak traced to needle reuse, saline
Unusual genotype eases identification of cluster
A glaring infection control violation and an unusual genotype of hepatitis C virus were key findings in what may be the largest reported HCV outbreak in an outpatient setting.
In an outbreak that apparently continued for more than a year before it was detected, 82 patients in an oncology clinic in Nebraska were infected with HCV, an epidemiologist reported recently in Washington, DC, at the annual conference of the Society for Healthcare Epidemiology of America (SHEA).
"This is a large — if not the largest — HCV outbreak in an outpatient clinic setting," said Alexandre Maedo de Oliveira, MD, MSc, a medical epidemiologist at the Centers for Disease Control and Prevention (CDC). "A single genotype was spread from patient to patient through exposure to contaminated, shared, saline solution bags. Reuse of syringes [also] played a role in the mechanism of this outbreak."
Though the clinic shut down as public health investigators conducted the investigation, they were able to trace the outbreak back to an index patient and a health care worker with a reckless disregard for infection control. "Considering that the source patient was enrolled in the clinic in March 2000 and no cases were seen among patients whose first visit occurred after June 2001, we believe that the outbreak was in place from March 2000 to June 2001," he said.
Investigators contacted all patients seen at the clinic from March 2000 through December 2001. They reviewed medical records, conducted patient interviews, and tried to determine the infection control practices, or lack thereof, in the oncology clinic.
A case was defined as a laboratory-confirmed HCV infection in a clinic patient without previous HCV infection. The date of infection onset was approximated by the first date on which abnormal liver function — as indicated by alanine aminotransferase levels — was recorded.
Of 613 clinic patients, 486 (79%) underwent serologic testing; 82 (17%) case patients were identified, all of whom first came to the clinic before July 2001.1 HCV genotype 3a was present in all 78 samples genotyped. Date of onset information was available for 54 (65.9%) case patients. A patient with prior HCV infection with genotype 3a was the probable source patient.
"The patient with previous HCV genotype 3a infection started treatment at the clinic in March 2000," de Oliveira said. "Several patients reported that syringes contaminated with blood were routinely reused to draw catheter flushed solution from shared saline bags. This infection control practice was changed in September of 2001. In October 2002, one month after the initial investigation, the clinic, not surprisingly, was closed by the owner’s decision."
Investigators found that case patients were more likely to have undergone flushing of central venous catheter (CVC) lines and venous infusions. Syringes used to draw blood for CVC lines were reused to draw flushing solution from shared saline bags. Despite the negative pressure applied to the syringe, blood was aspirated into the saline bags. As a result, the bags were contaminated with HCV-laced blood from the index patient. HCV was then spread among clinic patients as contaminated saline bags were used to flush catheters in other patients.
There was some question in SHEA discussions whether the outbreak may have gone undetected if not for the unusual 3a genotype, which is responsible for only about 7% of HCV infections nationally. Though conceding that many HCV infections go unexplained, David Henderson, MD, the session moderator and medical epidemiologist at the National Institutes of Health Clinical Center in Bethesda, MD, said he doubted many such outbreaks go undetected.
"If you look at the literature in the world, there are lots of outbreaks like this that occur, and almost all of them relate to some sort of practice that you or I wouldn’t endorse," he said. "On the other hand, probably a third of cases of HCV in our society don’t have a good explanation."
Apparently, a single health care worker — whose HCV status was not known to investigators — caused the outbreak by reusing syringes and aspirating patient blood into shared saline bags. "When we started this investigation, the health care professional who was probably implicated in this outbreak was no longer working," de Oliveira told SHEA attendees.
1. de Oliveira AM. Healthcare-related transmission of hepatitis C virus at an oncology clinic — Nebraska, 2000-2001. Abstract 235. Presented at the annual conference of the Society for Healthcare Epidemiology of America. Washington, DC; April 2003.