SPECIFIC CLINICAL DISORDERS



Infectious causes of diarrhea, the “gay bowel syndrome,” and food poisoning will be discussed briefly. The evaluation and differential diagnosis of malabsorption is covered in Chapter 36C and inflammatory bowel disease in Chapter 40.

Bacterial and Viral Infections. Acute watery diarrhea in the United States is most commonly due to viruses (rotavirus, Norwalk agent, coronavirus, parvovirus, and adenovirus] or entero-toxin-producing Escherichia coli. Campylobacter fetus (ss jejuni], Shigella, Salmonella, or Yersinia enterocolitica, less commonly seen, may produce either watery (secretory] diarrhea or dysentery with mucosal invasion, bloody diarrhea, chills, fever, tenesmus, and crampy pain. All of these agents, as well as the classic Vibrio cholera, also may be responsible for traveler’s diarrhea (all of these agents are discussed more fully in Chapter 92). Elaborate diagnostic studies and antibiotic therapy are warranted only for severe, protracted illness or when fever and signs of toxicity indicate bacteremia. Daily prophylaxis for traveler’s diarrhea with antibiotics (doxycycline, 100 mg) or bis­muth subsalicylate (Pepto-Bismol, 60 ml qid) is effective. However, use of antibiotics in this re­gard should be discouraged in order to (1) avoid emergence of resistant strains, (2) prevent anti­biotic-associated side effects, and (3) prevent pseudomembranous enterocolitis.
Antibiotic-associated Diarrhea. Five to 25 per cent of individuals receiving broad-spectrum an­tibiotics will develop diarrhea, usually within 2 to 20 days. The antibiotics most frequently im­plicated include ampicillin, clindamycin, linco-mycin, and cephalosporins. Diarrhea is usually due to an enterotoxin produced by Clostridium difficile, a bacterium that proliferates in the colon when the normal flora is disrupted. Diarrhea maybe mild but can be quite severe, with development of pseudomembranous colitis, characterized by inflammation, mucosal necrosis, ulceration, and pseudomembrane formation. The diagnosis is readily confirmed by assay of the stool for C. dif­ficile toxin and by sigmoidoscopy to visualize tbe characteristic pseudomembranes. Oral vancomy­cin is effective in eliminating the toxin-producing organism. Oral metronidazole may also be effec­tive (and is less expensive), and oral cholestyra­mine has been used to bind the toxin. Relapses, associated with persistence of C. difficile, occur in up to 20 per cent of individuals and respond to a second course of therapy.

Parasitic Infection. Giardia lamblia, a proto-zoon that resides on the mucosal surface in the proximal small bowel, usually causes acute, self-limited, watery diarrhea. It is spread via contam­inated water and may infect travelers, particularly in the Rocky and Sierra Nevada Mountains. Chronic infection may cause malabsorption. En­tamoeba histolytica, another water- or food-borne parasite, resides in the colon, where it may invade the mucosal wall, producing inflammation, char­acteristic undermined ulcers, and bleeding, a pic­ture that may resemble idiopathic ulcerative co­litis. Another complication of E. histolytica is hepatic abscess (see Chapter 47). Other parasitic diarrheas are rare in the United States; however, Strongyioides stercorals may occur in travelers.

Sexually Transmitted Diarrheal Diseases. Acute diarrhea is encountered as a sexually trans­mitted disease, often in homosexual males, and may be due to infection with one or more organ­isms, including Campylobacter, Shigella, Chla­mydia, herpes, gonococci, E. histolytica, Sal­monella, Giardia, and Cryptosporidium. Indeed, 40 per cent of male homosexuals harbor gastroin­testinal pathogens. These patients often present with proctitis (herpes, gonococci), colitis, or en­teritis. The evaluation of these patients usually requires careful inspection of the perianal area for uclers (herpes, syphilis), anoscopy and sigmoi­doscopy to evaluate the extent and severity of rectal and colonic mucosal disease, smears for Gram’s stain (gonococci), culture and examina­tion of smears or stool specimens for bacteria or ova and parasites, and VDRL serology. Those in whom anoscopy is normal and fecal leukocytes are absent but who have complaints of diarrhea, bloating, and abdominal cramps should be con­sidered to have small bowel infection or enteritis.

Enteric protozoan infections should be looked for, especially Giardia lamblia. Since multiple path­ogens are often present, an extensive evaluation should be undertaken and all identified patho­gens treated. Homosexual men are also frequently colonized with nonpathogenic parasites (such as Entamoeba nana), which do not require therapy.

Food Poisoning. Food poisoning is defined as a set of clinical syndromes resulting from the ingestion of food that is contaminated either with (1) bacteria or their toxins, (2) poisonous chemi­cals, or (3) poisonous plants or animals. Although some types of food poisoning are recognizable by their unique extraintestinal manifestations, others are only identifiable if they occur in outbreaks where a number of individuals develop a similar illness. The most common types of food poisoning are summarized in Table 36-12.

Bacterial food poisoning may be due to inges­tion of preformed toxin, such as the heat-stable toxins of Clostridium botulinum, Staphylococcus aureus, and Bacillus cereus. C. botulinum is an anaerobic organism that produces a neurotoxin in improperly canned foods (see Chapter 92). S. au­reus and B. cereus grow in cooked food that is inadequately cooled. Other types of bacterial food poisoning result from infection with live organ­isms or spores (Clostridium perfringens and Vi­brio parahaemolyticus). The bacterial food poi­sonings are generally short, self-limited illnesses that often end about the time the patient seeks medical help. Therapy is supportive and symp­tomatic, the primary goal being to restore extra­cellular fluid volume, with parenteral fluids if necessary. Antibiotics are usually not indicated. In protracted cases of V. parahaemolyticus infec­tion, treatment with tetracycline or ampicillin may shorten the illness.