TORONTO — A new study by Montreal researchers suggests rates of C. difficile in non-hospitalized people may be rising, even among people who haven't been taking antibiotic drugs - something previously thought to be a requisite precursor to infection.

The findings seem to point to changes in the Clostridium difficile bacterium that may be making C. difficile easier to pick up outside of hospitals, experts suggest.

"That is really a remarkably high increase in cases," Dr. Dale Gerding, a leading U.S. expert in the field, said of the findings of the study led by Dr. Sandra Dial of McGill University. Gerding was not involved in the work.

"I think this needs verification in another database, to tell you the truth. And it may be that it's true. And it may be that there's something going on."

Dial and her co-authors searched a large British database for cases of C. difficile diagnosed among people in that country who had not been hospitalized in the year prior to developing infection. Their study was published Wednesday in the Journal of the American Medical Association.

C. difficile is typically viewed as a hospital disease, with the overwhelming majority of cases occurring within health-care facilities.

The difficulty of eradicating C. difficile spores once an environment has been contaminated by an infected patient makes the bug easier to contract in hospitals. And high rates of antibiotic use in institutions leave patients susceptible to the bacterium. (Antibiotics alter the natural flora of the bowel, allowing C. difficile to take hold and take over.)

Dial found that from 1994 to 2004, the rate of cases in the community rose steadily in Britain, from about one case per 100,000 at the start to 22 per 100,000 at the end of the period.

Gerding, associate chief of staff for research at the Hines Veterans Affairs Hospital in Chicago, said the increase was "very alarming."

More startling still was the fact that only 37 per cent of the people infected had been prescribed antibiotics in the 90 days prior to their infection.

"That floors me a little bit," said Dr. Clifford McDonald, a C. difficile expert based at the U.S. Centers for Disease Control in Atlanta.

The study found that people taking powerful antacid drugs known as proton pump inhibitors - Nexium is one - were three times more likely to develop C. difficile than people who weren't taking the drugs.

And they found that people taking prescription painkillers known as NSAIDs -- non-steroidal anti-inflammatory drugs -- were also at an elevated risk of developing C. difficile.

Dial admitted her team wasn't expecting that latter finding. "We actually stumbled upon that," she said.

Gerding and McDonald have led research efforts in the United States which have shown an epidemic strain of C. difficile has arisen in their country.

That strain, which produces massively higher toxin levels than traditional strains, is also responsible for the serious outbreaks of C. difficile that have plagued hospitals in parts of Quebec for the past couple of years.

McDonald said these findings suggest that some other genetic changes may also be taking place, changes that allow for easier infection in the absence of antibiotic exposure.

"The epidemic strain is ... the latest permutation in this organism. But there might have been some permutations going on below the radar screen before this," he said.

"And they might be what's more responsible for some of the early increase both in this country" -- the United States -- "(and) this community stuff in Great Britain.

"Maybe there are some other genetic changes. I think we need to keep our mind open. Think beyond the epidemic strain."