Superbug on the march

There has been a dramatic increase in the number of cases of Canadians becoming infected or colonized by the superbug MRSA since 1995, both in hospitals and within the community, a study has found.

TORONTO — There has been a dramatic increase in the number of cases of Canadians becoming infected or colonized by the superbug MRSA since 1995, both in hospitals and within the community, a study has found.

Researchers who conduct national surveillance of infectious diseases found that between 1995 and 2007, the incidence of MRSA — methicillin-resistant Staphylococcus aureus — soared 17-fold at Canadian hospitals.

Over the 13-year period, there was also a three-fold jump in the number of MRSA infections associated with more virulent strains from the community, say researchers from the Canadian Nosocomial Surveillance Program, who conducted the study based on data from 48 sentinel hospitals across the country.

“This is the most comprehensive and representative picture we have to date of MRSA in Canada,” said lead author Dr. Andrew Simor, chief of microbiology and infectious diseases at Sunnybrook Health Sciences Centre in Toronto. “This surveillance is the first in Canada to be able to link clinical and epidemiologic data — for example, the types of patients who are most at risk — with well-characterized laboratory isolates (bacterial strains), where we can match a specific patient to a specific isolate, to further our understanding of the impact of MRSA on hospitalized patients,” Simor said.

To conduct the study, researchers analyzed hospital data and identified 37,169 patients with either MRSA infection or colonization. The research also included lab tests to isolate and type the various MRSA strains affecting patients. They found the overall incidence of MRSA increased to more than 11 per 10,000 patient days in 2007 from 0.65 per 10,000 patient days in 1995. Infections associated with MRSA strains from the community also rose significantly, to 23 per cent in 2007 from six per cent in 1995.

“From a global perspective, this surveillance shows that Canada needs to be doing better,” said Simor.

“We need to continue to be vigilant in controlling this infection … and developing more effective interventions to control the rapid emergence of more virulent CA-MRSA strains from the community that have now been introduced into hospital settings in Canada.”

CA-MRSA is the acronym used to describe cases of drug-resistant Staph caught in the community, not in hospitals.

Strains caught in hospitals are generally different from those caught outside hospitals. Staphylococcus aureus bacteria are commonly found on the skin and can cause a range of problems, from a minor infection in a cut to life-threatening disease. MRSA strains are those that have become immune to the effects of the main antibiotics used to combat the bacteria.

The superbug is a major cause of infection picked up by patients within hospitals — known as a nosocomial infection — but it has increasingly emerged as a significant infection among people living in the community.

When a person is infected with a bacterium or virus, the organisms multiply and can cause injury to a specific tissue or illness throughout the body.

With colonization, a person carries the microbe — for instance, on the skin, in the mouth or in the digestive system — without developing disease. They can, however, pass it to another person, who may become infected.

Simor said older adults with underlying medical conditions who have been admitted to hospital are at the greatest risk of contracting MRSA.

“It is still mostly a hospital-acquired infection,” he said in an email interview. “However, in the past five years, there has been a dramatic increase in MRSA occurring in children and younger adults who have no hospital contact or exposure.”