Researchers have now shown that the gastrointestinal illness that spread to various hospitals across the world was caused by two different but related strains of Clostridium difficile. One of the strains originated in the U.S. while the other came from Canada.

The outbreak occurred between 2002 and 2006 in hospitals across UK, U.S.A., Canada and Europe. Researchers from Wellcome Trust Sanger Institute tracked the bacteria that had caused the illness by using DNA sequencing. Researchers were able to determine the source as well as track its spread across the countries.

"We found that this outbreak came from two separate epidemic strains or lineages of C. difficile, FQR1 and FQR2, both emerging from North America over a very short period and rapidly spread between hospitals around the world," said Dr Miao He, first author from the Wellcome Trust Sanger Institute in a news release.

C. difficile produces highly resistant spores. These spores help the organism survive harsh conditions and spread to other geographical areas. The strains of C. difficile infection linked with the outbreak had developed resistance to a commonly used drug, researchers say.

The research team obtained samples from patients admitted in various hospitals around the world between 1985 and 2010. Using genetic history to map both epidemic strains, researchers were able to show that the two strains of C. difficile had acquired resistance to fluoroquinolone separately.

"Up until the early 2000s, fluoroquinolone was an effective treatment for C. difficile infection. We've seen that since these strains acquired resistance to this frontline antibiotic, not only is it now virtually useless against this organism, but resistance seems to have been a major factor in the continued evolution and persistence of these strains in hospitals and clinical settings," said Professor Brendan Wren, author from the London School of Hygiene and Tropical Medicine.

The origins of one strain of C. difficile called FQR1 was traced back to U.S.A. the strain spread through many hospitals in the country. A few sporadic cases of this strain were also seen in Switzerland and South Korea.

The second strain called FQR2 originated in Canada and spread to North America, Australia and Europe.

Researchers say that the study shows that the hospitals in the world are interconnected.

"We have exposed the ease and rapidity with which these fluoroquinolone-resistant C. difficile strains have transmitted across the world. Our research highlights how the global healthcare system is interconnected and how we all need to work together when an outbreak such as this occurs," said Dr Trevor Lawley, lead author from the Wellcome Trust Sanger Institute.

The study is published in the journal Nature Genetics.

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