Lab outbreak of Shigella spreads via faucet handles
A cautionary tale of a test that led to chaos
An outbreak of Shigella sonnei in a microbiology lab apparently began through inappropriate specimen handling by a lab student, spreading to six other technicians via contaminated faucet handles on the lab sink, an investigating epidemiologist reports.
In an outbreak that occurred from Jan. 23-28, 1996, six of 20 medical technologists in a hospital microbiology lab became ill with stool-culture-confirmed S. sonnei with the same antibiogram, reports Leonard Mermel, DO, ScM, director of infection control at Rhode Island Hospital in Providence and assistant professor at Brown University School of Medicine.
An S. sonnei clinical specimen had not been identified in the lab since three weeks before the outbreak, and that isolate did not match the outbreak strain. It was then discovered that a med tech laboratory student had been given S. sonnei as an unknown specimen to identify as part of a routine laboratory examination. While other lab techs washed hands rather than routinely donning and changing gloves, the student wore gloves for all lab work. He recalled one instance of directly handling the test specimen with his gloved hands rather than using a stir rod, Mermel says.
’That was two days before the first case and we suspect that somehow if he heavily contaminated his gloves he may have contaminated environmental surfaces such as a faucet handle,” he tells Hospital Infection Control.
All those infected were working in the main bacteriology section of the microbiology lab, where one sink is used for hand washing with handles for hot and cold water.
’We found that a sink that was used for handwashing in the clinical lab had been changed from a foot-pedal-operated sink to a faucet-handled sink,” he says.
Paper towels did the trick
The handles could not be tested for the pathogen, as the lab had already been thoroughly disinfected as an initial control measure. However, a case-control study looking at risk factors gave some statistical significance to the suspicions, as lab techs who reported routinely using a paper towel as a barrier when touching the faucet handles were less likely to be infected.
’That is an old-fashioned infection control maneuver,” Mermel notes. ’But 11 of 14 non-infected lab techs did use that barrier technique, whereas only one of six [infected] cases did, so that was highly statistically significant.”
Indeed, touching faucet handles when using the sink without placing a paper towel between hands and the handles was the only risk factor that reached statistical significance. No new cases have occurred after the additional cleaning and installing a handle-free sink, activated by infrared light, he notes.
’I think faucet handles in hospitals are something of an antiquated idea,” Mermel says.
So is giving students an isolate such as Shigella as an unknown to identify, at least at the Providence hospital, he notes. The source isolate was typical of a standard clinical isolate and was not an unusually infectious specimen, but the pathogen particularly S. flexneri is capable of spreading rapidly once introduced into a lab environment.1
’Shigella is one of the most highly infectious diarrheal agents known,” Mermel says. ’It could have happened with something else, but it is one of the more easily transmitted organisms.”
Interestingly, the lab student did not develop infection, but the six laboratory technicians were not so fortunate. Their symptoms included bloody diarrhea, fever, abdominal pain, chills, headache, and back pain. Their lost wages totaled $10,000 and the outbreak caused considerable disruption in the lab, he adds. While some workers were only out briefly, one veteran lab tech developed a kind of post-traumatic stress syndrome from the incident and did not return for to work for nearly two months, Mermel says.
’The economic impact was significant,” Mermel says. ’It had a big impact on the lab it was fourth of the lab [staff], but most of them were sick for a relatively short period of time. It caused a lot of chaos. People were very skittish about working up there.”
Reference
1. Grist NR, Emsilie JAN. Infection in British clinical laboratories, 1986-1987. J Clin Pathol 1989; 42:677-681.
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