Abstract & Commentary

Clostridium difficile BI: From Canada to the Second City

By Joseph F. John, MD, FACP, FIDSA, FSHEA, Associate Chief of Staff for Education, Ralph H. Johnson Veterans Administration Medical Center; Professor of Medicine, Medical University of South Carolina, Charleston, is Associate Editor for Infectious Disease Alert.

Dr. John reports no financial relationship to this field of study.

Synopsis: Severe disease was common and crude mortality was considerable among patients diagnosed with Clostridium difficile in Chicago in February of 2009. The BI strain was the predominant strain identified (61%).

Source: Black SR, et al. Clostridium difficile outbreak strain B1 is highly endemic in Chicago area hospitals. Infect Control Hosp Epidemiol 2011;32:897-902.

A 1-month prevalence study was done in 2009 at 25 of the 56 contributing hospitals participating in the Chicago Health Alert Network. Patients were considered having Clostridium difficile infection (CDI) if they had three or more watery stools and a positive C. difficile toxin or pseudomembranous colitis. Severe CDI was defined as having CDI requiring ICU care. Rates were calculated per 10,000 patient-days during the month of February, 2009. Stool samples were collected and cultured. C. difficile isolates were characterized for HindIII restriction endonuclease analysis (7 groups). Note that only hospital onset cases were included in the study.

Of the 56 network hospitals, 25 contributed data and samples to this study. There were 263 incident episodes and, of these, 16% were considered severe and 57% were females. Twenty patients died, so the crude mortality rate was 8%. Thirty-seven percent of the patients had to extend care at a long-term care facility where the average length of stay (LOS) was 7 days.

Restriction enzyme analysis found that the majority were BI (61%), followed by J, G, BK, CF, Dh, or K. There were 22% non-epidemic groups that were not further characterized. BI was present in hospital and community origin organisms. BI patients had a high likelihood (50%) of needing long-term care and 18% of the BI patients had severe outcomes. Note that BI was very widespread, occurring at 18 of the 20 health care facilities.


Hats off to the wonderful consortium of hospitals constructed in the Chicago Health Alert Network. Managing to organize 25 organizations of any kind in a large U.S. city is a great accomplishment, including the submission of 129 specimens that yielded a cultured organism. The major point of this study is that a highly virulent strain that originated in Canada1 — one that has come to be known as the B1 strain — has infiltrated the lower 48 and, in at least one major city, it has become endemic, causes community as well as hospital disease, and can be fatal in up to 8% of episodes.

Can we do anything to control the spread of such a virulent enteropathogen? America knows how to build reporting networks. Reported on PBS Frontline, Sept. 6, 2011, there are a series of highly secret, yet very functional, antiterrorist nodes throughout the country. Assuming these nodes have been effective in thwarting terror events, perhaps they provide models better than ones we have built to alter the occurrence and spread of specific events. Perhaps a city like Chicago could enhance its efforts to limit spread of virulent pathogens. The authors do emphasize that one outgrowth of the current study is the need for close communication between acute care facilities.

The notorious B1 strain, as discovered in this intriguing study, was prominent throughout Chicago hospitals in 2009. Why did the strain delay its entry into the heartland, yet predominate when it did? Answers to the first part of the question remain without explanation. As for the second question, there is likely some colonization advantage for this strain, once introduced, that showed vicious virulence during its Canadian phase, enough that hospitals had to be closed.

From the data in this article, it is clear that B1 has spread into the heartland of North America. With the leadership of this hospital consortium, Chicago has given us a model to allow cities to have early alerts and to cooperate in assembling a holistic molecular epidemiology of pathogen spread.


  1. Pepin J, et al. Clostridium difficile-associated diarrhea in a region of Quebec from 1991 to 2003: A changing pattern of disease severity. CMAJ 2004;17:466-472.