difficile is a gram-positive, toxin-producing anaerobic rod that is the causative agent of pseudomembranous colitis The most common antibiotics associated with C difficile in children reflect antibiotics most commonly used in the outpatient setting: penicillins, cephalosporins, clindamycin, and macrolides Other risk factors include use of feeding tubes, proton pump inhibitors, immunocompromise, and recent hospitalization Colitis with C difficile varies widely in severity Typically, profuse watery or mucoid diarrhea begins after several days of antibiotic therapy Many older children complain of crampy abdominal pain On examination, the usual findings include fever and diffuse abdominal tenderness Often, the WBC count rises above 15,000/mm3 The stool may be guaiac-positive or frankly bloody; leukocytes (by stool microscopy or by measuring stool lactoferrin) are found in approximately 50% of patients An etiologic diagnosis requires the identification of C difficile toxin in the stool; recovery of the organism on culture is suggestive but not sufficient The diagnosis is more difficult in children less than years of age, who can have asymptomatic intestinal colonization by toxigenic C difficile If C difficile colitis goes unrecognized and untreated, complications, including toxic megacolon, perforation, and peritonitis, may develop Case fatality rates as high as 10% to 20% were described before the introduction of specific treatments Treatment of asymptomatic carriers is not recommended Mild cases without fever or other systemic signs of infection may resolve with discontinuation of the inciting antibiotic(s) and supportive care Treatment of moderate to severe infection, defined as pyrexia, voluminous diarrhea, dehydration, colitis, or leukocytosis, warrants systemic therapy Oral metronidazole (30 mg/kg/day in four divided doses; maximum: g/day) is the first-line choice for initial treatment of mild/moderate disease and for treatment of the first relapse Oral vancomycin (40 mg/kg/day in four divided doses; maximum: 500 mg/day) can be used for refractory cases, as up to 20% of patients may relapse Severe cases may require both oral vancomycin and intravenous metronidazole (same dose as for oral administration) Treatment should continue at least 10 days Antidiarrheal agents should be avoided Contact precautions should be used Alcohol-based hand hygiene products not kill spores; instead, providers should wash their hands with soap and water Intra-Abdominal Abscesses The most common cause of intra-abdominal abscesses in childhood will be from perforated appendicitis Blood cultures rarely are positive unless the child is immunocompromised or toxic appearing These infections are polymicrobial, and cultures often grow a combination of gram-negative enterics and anaerobes As such, broadspectrum antimicrobial coverage should be offered The Infectious Disease Society of America has published guidelines for empiric therapy for children with complicated intra-abdominal infections Monotherapy has been found to be equivalent in terms of outcomes to combination therapy Single-agent regimens include piperacillintazobactam, and carbapenems (e.g., meropenem, ertapenem) for children with community-acquired infections Recommended multidrug regimens include a third-generation cephalosporin with metronidazole; metronidazole or clindamycin with an aminoglycoside, with or without ampicillin GENITOURINARY INFECTIOUS EMERGENCIES Urinary tract infections (UTIs) and renal abscesses are discussed in this section The diagnosis and management of children with pelvic inflammatory disease are covered in Chapter 92 Gynecology Emergencies Urinary Tract Infections CLINICAL PEARLS AND PITFALLS The most common pathogen causing UTIs is E coli; in many regions, over 50% of E coli isolates from the urinary tract are resistant to amoxicillin and/or TMP-SMZ UTIs are on the differential diagnosis of fever of unknown origin and of failure to thrive in infants Most children outside the neonatal period who have UTIs can be managed in the outpatient setting Isolation of S aureus from a urinary culture should prompt evaluation for a renal abscess Current Evidence Infections occur along the urinary tract from the tip of the urethra to the renal parenchyma Clinical syndromes that may accompany infections include urethritis, cystitis, and pyelonephritis Bacteriuria refers to the presence of