In particular, when the antibiotic kills off other competing bacteria in the intestine, any bacteria remaining will have less competition for space and nutrients. The net effect is to permit more extensive growth than normal of certain bacteria. C. difficile is one such type of bacterium. In addition to proliferating in the bowel, C. difficile also produces toxins. Without either toxin A or toxin B, C. difficile may colonize the gut, but is unlikely to cause pseudomembranous colitis. The colitis associated with severe infection is part of an inflammatory reaction, with the "pseudomembrane" formed by a viscous collection of inflammatory cells, fibrin, and necrotic cells. Diagnosis
Prior to the advent of tests to detect C. difficile toxins, the diagnosis most often was made by colonoscopy or sigmoidoscopy. The appearance of "pseudomembranes" on the mucosa of the colon or rectum is highly suggestive, but not diagnostic of the condition. The pseudomembranes are composed of an exudate made of inflammatory debris, white blood cells. Although colonoscopy and sigmoidoscopy are still employed, now stool testing for the presence of C. difficile toxins is frequently the first-line diagnostic approach. Usually, only two toxins are tested for—toxin A and toxin B—but the organism produces several others. This test is not 100% accurate, with a considerable false-negative rate even with repeat testing. Classification
CDI may be classified in non-severe CDI, severe CDI and fulminant CDI depending on creatinine and white blood count parameters.
People without a history of gastrointestinal disturbances due to antibiotic use or diarrheal illness are less likely to become colonized by C. difficile.In 2005, molecular analysis led to the identification of the C. difficile strain type characterized as group BI by restriction endonuclease analysis, as North American pulse-field-type NAP1 by pulsed-field gel electrophoresis  and as ribotype 027; the differing terminology reflects the predominant techniques used for epidemiological typing. This strain is referred to as C. difficile BI/NAP1/027. Risk factors
Antibiotics
C. difficile colitis is associated most strongly with the use of these antibiotics: fluoroquinolones, cephalosporins, and clindamycin.Some research suggests the routine use of antibiotics in the raising of livestock is contributing to outbreaks of bacterial infections such as C. difficile. Healthcare environment
People are most often infected in hospitals, nursing homes, or other medical institutions, although infection outside medical settings is increasing. Individuals can develop the infection if they touch objects or surfaces that are contaminated with feces and then touch their mouth or mucous membranes. Healthcare workers could possibly spread the bacteria or contaminate surfaces through hand contact. The rate of C. difficile acquisition is estimated to be 13% in those with hospital stays of up to two weeks, and 50% with stays longer than four weeks.Long-term hospitalization or residence in a nursing home within the previous year are independent risk factors for increased colonization.