An outbreak strain of Clostridium difficile, a bacterium that causes diarrhea and sometimes life-threatening inflammation of the colon, is common in Chicago-area acute care hospitals, an investigation published in the September issue of Infection Control and Hospital Epidemiology suggests. In response to Illinois Department of Public Health reports of rising rates of C. difficile infection as a hospital discharge diagnosis, the Chicago and Cook County health departments surveyed 25 Chicago-area hospitals over one month in 2009. They identified 263 total cases of C. difficile illness. Of 129 C. difficile isolates cultured from these patients, 61 percent were the outbreak C. difficile strain known as BI/NAP1. The BI strain, which is known to cause more serious illness, is usually associated with large acute outbreaks of C. difficile. However this investigation suggests that BI is endemic in the Chicago area and patients could be at risk for severe disease even in the absence of a large acute outbreak.