1. Viral. Usually resolves in a few days and can be treated symp-tomatically. Rotavirus, adenovirus, and Norwalk virus are more common.
2. Bacterial. Shigella dysenteriae, S sonnei, Salmonella spp, Campylobacter jejuni, Yersinia spp, and enterohemorrhagic Escherichia coli cause diarrhea by enteroinvasion. Staphyl-ococcus aureus, E coli, Vibrio cholerae, Vibrio parahaemolyti-cus, Clostridium perfringens, Clostridium difficile, and some Shigella species cause diarrhea by producing enterotoxins. Spectrum of illness may range from asymptomatic to life threatening. S aureus and C perfringens are often associated with food poisoning. Enterohemorrhagic E coli causes bloody diarrhea and may be associated with hemolytic uremic syndrome.
3. Parasitic. Giardia lamblia is often contracted by drinking contaminated water and can cause abdominal distention, diarrhea and, at times, failure to thrive. Giardia is easily passed by the fecal-oral route and is particularly troublesome in day-care centers and schools. Entamoeba histolytica produces severe colitis; however, it is generally acquired only by travel to developing countries. Cryptosporidium can cause a self-limited diarrhea in immunocompetent individuals or severe, unremitting diarrhea in patients with an immune deficiency.
B. Postinfectious State. Several viruses can cause severe enteritis resulting in prolonged intestinal mucosal damage, acquired carbohydrate intolerance, and malabsorption in infants. Patients present initially with fever and diarrhea, followed by intractable watery diarrhea that may resolve in as short a time as 2 weeks or last as long as several months.
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