thrombocytopenia, and acute kidney injury Children are affected most often in the first years of life They often present with abdominal pain, vomiting, and diarrhea that become bloody Five to 10 days after onset of diarrhea, children with HUS develop pallor, petechiae, and decreased urine output The most common cause of HUS is Shiga-like toxin-producing Escherichia coli (E coli 0157:H7) Pseudomembranous colitis is another serious disorder that may cause bloody diarrhea Clinically, the child with pseudomembranous colitis appears ill with prostration, abdominal distention, and blood in the stool This disease results from an overgrowth of toxin-producing Clostridium difficile, usually as a result of destruction of the normal intestinal microflora It may occur at any age but is uncommon in early childhood Although the incidence of pseudomembranous colitis is highest after treatment with clindamycin, studies have shown that exposure to any antibiotic increases susceptibility to C difficile infection In fact, because of its common use, amoxicillin is responsible for most cases of pseudomembranous colitis in childhood, even though overall incidence of C difficile infection after therapy with this agent is low Occasional cases occur in children with no recent usage of antibiotics