Colonic epithelial lymphocytosis associated with an epidemic of chronic diarrhea.

The term Brainerd diarrhea has been applied to outbreaks of chronic watery diarrhea of unknown etiology characterized by acute onset and prolonged duration. Our aim was to describe the histologic changes in gastrointestinal biopsy specimens from patients with Brainerd diarrhea. We examined 52 colonic and 12 small bowel biopsy specimens from 22 patients who were involved in an outbreak of Brainerd diarrhea that was linked to the water supply of a cruise ship visiting the Galapagos Islands. Small bowel biopsy specimens from seven patients were histologically normal. One patient had a duodenal biopsy specimen that resembled celiac sprue. Colonic biopsy specimens from 20 patients revealed surface epithelial lymphocytosis without distortion of mucosal architecture, surface degenerative changes, or thickened subepithelial collagen plates. The degree of surface epithelial lymphocytosis was greater than that seen in control groups of persons with normal colons, acute colitis, and ulcerative colitis (p < 0.001), similar to that seen with collagenous colitis, and less than that seen with lymphocytic colitis (p < 0.001). Three patients showed focal active colitis similar to that described in acute infectious-type colitis in addition to the epithelial lymphocytosis. Two patients had colonic biopsy specimens that were histologically normal. In summary, histologic abnormalities in the small bowel are generally absent in Brainerd diarrhea. Colonic biopsy specimens in Brainerd diarrhea frequently show epithelial lymphocytosis similar to that seen in collagenous and lymphocytic colitis. Although currently Brainerd diarrhea can be diagnosed only with epidemiologic data indicating an epidemic and a point source, the lack of surface degenerative changes and the relatively lower lymphocyte counts seen in our cases of Brainerd diarrhea may serve to distinguish it from lymphocytic colitis, and the lack of a thickened subepithelial collagen plate distinguishes it from collagenous colitis.