About one in three elderly people admitted to hospital require treatment with antibiotics. About 20% of these patients will develop Clostridium difficile disease (CDD), an antibiotic-associated diarrhoea, which typically occurs 2-8 weeks after exposure to antibiotics. Antibiotic exposure is the main risk factor for CDD, which can result in pseudomembranous colitis complicated by toxic megacolon and high case-fatality. The cost to health services is estimated at £4000 per case of CDD. Relapse of Clostridium difficile occurs in 10 to 25 percent of patients treated with metronidazole or vancomycin. Furthermore, multiple relapses in the same patient are common, and up to 10 or more bouts of relapsing colitis have occurred in some patients. The number of cases of CDD among hospitalized children in the United States more than doubled over a 10-year period, according to a new study. The researchers found that the incidence of CDD in hospitalized children increased from 3,565 cases in 1997 to 7,779 cases in 2006. Children with CDI had a 20 percent greater risk of death and a 36 percent higher risk of requiring surgery to remove part of or the entire colon. In addition, children diagnosed with CDI were four times more likely to have an extended hospital stay and twice as likely to have higher hospital costs than hospitalized children not infected by C. difficile.