C. difficile strain 20 times more virulent

The strain of Clostridium difficile circulating in Quebec and reported in CMAJ last year [171:19-21] was associated with a greater severity of illness than is typical of the organism.

Evidence presented at the Apr. 11, 2005, meeting of the Society for Healthcare Epidemiology of America demonstrates the C. difficile strain in Quebec produced 20 times the levels of toxins A and B than previously studied strains.

“The ability of this emerging strain to produce high levels of toxins A and B in the laboratory may explain its virulence in patients,” says Michel Warny, director of bacterial process development for Cambridge, Mass.– based Acambis.

Dr. Jacques Pépin, an infectious disease expert at the Centre hospitalier universitaire de Sherbrooke (CHUS) and a coauthor of the study, says the research “just confirms what clinicians had been seeing for the last couple of years.” Acambis is developing a vaccine against C. difficile and worked with the US Centers for Disease Control, using samples from Sherbrooke patients.

The hypervirulent strain is identical to one that caused outbreaks in hospitals in 6 US states. It has also been identified at Toronto's Princess Margaret Hospital, where it caused a cluster of cases and a death last fall.

Although the US outbreak was sizeable, hospitals were able to bring it under control more quickly. Almost 2 years after the outbreak began in Quebec, hospitals still experience cases caused by the same strain.

“The question is why did it reach such dramatic proportions here?” Pépin asks. “I think it has to do with the decay of our hospital infrastructure.”

Earlier this year, the Quebec Ministry of Health allocated $20 million for infection control at affected hospitals. The Sherbrooke region got $900 000. Most of it was spent on bills for measures implemented in the previous 6 months, Pépin says.

This past winter, the CHUS had a third to half the number of cases, compared with the previous 2 years, when 100 patients died, says Pépin. But the proportion of people who required colectomies or died has remained the same, he says.

“I think this hypervirulent strain is more transmissible than other strains,” he says. “I don't see why it would go away — I think it's going to stay here.”