Chronic Diarrhea

Chronic Diarrhea 

A 21 year-old male presents with a 6-week history of watery diarrhea

and crampy abdominal pain. He reports that the diarrhea has not been constant and has alternated with periods of constipation. For the past 2 weeks, the diarrhea has been blood-streaked and he has had several weeks of midepigastric pain. He spent the past 6 months in a rural community in Guatemala participating in a community service project sponsored by his college. He returned from Guatemala just 10 days ago. While there, he drank the water and ate the food available in the local community, and he did not routinely boil water for drinking. He denies antibiotic exposure but has taken mefloquine weekly for malaria prophylaxis. Two separate stool specimens taken by student health when he returned were

reported as negative for Salmonella, Shigella, Campylobacter, E. coli O157:H7, Yersinia, Aeromonas, and Pleisiomonas as well as Giardia lamblia. On physical examination he appeared well nourished and well developed but reports an 8–10 lb weight loss. 

LABORATORY TESTS

Just as with acute diarrhea, the history of a patient’s illness frequently

provides clues to the etiology of the disease. The length of illness and

travel history of this patient plus abdominal findings and weight loss

are key features. Diarrhea with blood narrows infectious causes to agents such as Shigella, Salmonella, Campylobacter, EHEC, EIEC, and Entamoeba histolytica. An evaluation for chronic diarrhea requires a stool culture (×3), ova and parasite exam of stool (×3), and guaiac test of stool for occult blood. Because of this patient’s abdominal findings, liver function tests such as alkaline phosphatase and serum transaminases should also be ordered. Whenever liver abscess is suspected, abdominal ultrasound or computed tomography (CT scan) should also be performed.

Because both bacteria and parasites can be shed intermittently in stool, multiple stool specimens should be submitted for both bacterial culture and ova and parasite examination. See Case 3 for information on stool collection and transport for bacterial culture. For parasite analysis, specimens should be taken on separate days (every other day if possible) to increase likelihood of detection. Stool specimens collected for parasite analysis should be submitted in preservation vial(s) designed for this purpose.

  All forms of parasites (ova, larvae, protozoa, worms) can be

maintained at room temperature for long periods of time (months) using preservation vials. In addition, concentration procedures to recover small numbers of protozoan cysts, eggs, and larvae can be performed using the vials, and permanent stained smears can be prepared as well. If preservation vials are not available, then stool should be collected in clean, dry, wide-mouthed containers with tight-fitting lids. The stool should not be contaminated with urine because the pH of urine can destroy motile parasites. Liquid stool specimens must be examined by the laboratory within 30 min after they were taken from the patient, or some parasitic forms will disintegrate. If this rapid transport time is not possible, then preservation vials should be used. Results of an initial ova and parasite stool examination showed that the specimen was positive for cysts of E. histolytica/E. dispar. With this additional information, a serology test for E. histolytica antibodies and an abdominal CT scan were ordered.

E. histolytica, the cause of intestinal amebiasis and amebic liver abscess, can be diagnosed in the laboratory using a variety of methods:

1. Microscopic exam (stool, liver abscess). Microscopic identification of E. histolytica cysts or trophozoite (ameboid) forms is the most common method used to diagnose the infection; however, it is both insensitive and nonspecific. The test is nonspecific because E. histolytica cysts cannot be morphologically distinguished from those of Entamoeba dispar, a harmless commensal, unless ingested RBCs are present inside the trophozoite. Microscopic examination of liver abscess material is a poor way to attempt the diagnosis of amebiasis. While the abscess material is known to have the appearance of “anchovy paste,” ameba are rarely visualized in the material because they have disintegrated.

2. Antibody detection (serum). Serology studies [indirect hemagglutination, gel diffusion, enzyme-linked immunosorbent assay (ELISA)] to detect antibody to E. histolytica are positive in >90% of patients who have invasive disease. In the vast majority of patients antibodies are detectable after 7–10 days. When patients no longer have detectable parasites in their stools, detection of antibodies is critical for diagnosis of amebic liver abscesses.

TREATMENT AND PREVENTION

Two classes of drugs are used to treat E. histolytica infections. (1) a luminal amebicide, such as iodoquinol, which destroys parasites in the lumen of the intestine but does not kill ameba in tissue; and (2) a tissue amebicide, such as metronidazole or chloroquine, which treats invasive amebiasis but is less effective in the lumen. Amebic dysentery may be treated with iodoquinol and metronidazole. Extraintestinal disease is treated with a combination of

metronidazole and chloroquine. To follow the clinical response of intestinal disease to therapy, a repeat stool exam for parasites should be done 2–4 weeks after treatment, and extraintestinal disease should be monitored by repeat CT scans. Repeat serology tests are of little use since antibody titers remain elevated in spite of response to therapy. Prevention of infection with E. histolytica involves drinking boiled or bottled water when traveling to developing nations, and avoiding uncooked foods that may have been washed in water, such as salad.