C. difficile is an obligately anaerobic, gram-positive, spore-forming bacillus and causes diarrheal illness that is most commonly acquired in the hospital. The disease is acquired almost exclusively in association with antimicrobial treatment; virtually all antibiotics carry a risk of CDI.

• After C. difficile colonizes the gut, its spores vegetate, multiply, and secrete toxin A (an enterotoxin) and toxin B (a cytotoxin), causing diarrhea and pseudomembranous colitis. The rate of fecal colonization is often ≥20% among adult pts hospitalized for >1 week; in contrast, the rate is 1-3% among community residents.
• Spores can persist on environmental surfaces in the hospital for months and on the hands of hospital personnel who do not practice adequate hand hygiene.
• Rates and severity of CDI in the United States, Canada, and Europe have increased markedly in the past decade. The epidemic NAP1/BI/027 strain accounts for much of the increase and is characterized by production of 16-23 times as much toxin A and toxin B as is documented for control strains, by the presence of a third toxin (binary toxin), and by high-level resistance to fluoroquinolones.