[Chronic diarrhea: value of microbiology in diagnosis]

Chronic diarrhoea of the adult is defined as diarrhea during 30 days or longer. Frequent causes of chronic diarrhea in the immunocompetent adult without recent travel to developing countries are noninfectious processes, including laxatives misuse, diseases causing chronic maldigestion, osmotically active artificial sweeteners (i.e. sorbitol), hormonal disorders or drugs with intestinal side effects. Infectious agents as the cause of chronic diarrhea are important in two populations, namely in travelers returning from tropical countries bearing a significant risk of intestinal parasitic infections and in immunocompromised patients, especially AIDS patients with CD4 cell counts below 50 per microliter. Intestinal parasites and C. difficile, Y. enterocolitica, Shigellae and Cytomegalovirus are the most important causative agents of chronic diarrhea. Intestinal pathogens were identified in 46% of chronic, but only in 16.5% of acute diarrhea episodes of HIV-infected patients. An extensive medical history including recent travel as well as the detailed characteristics of onset of symptoms and of their time course is essential for the diagnosis. All patients should have a complete differential blood count, ESR, determination of electrolytes, liver enzymes, creatinine, blood glucose, and serum albumin. Tests to exclude hyperthyriodism, or pancreatic insufficiency as well as a d-xylose absorption test can be included, if appropriate. Microbiological-parasitological investigations are obligatory in patients with chronic diarrhea returning from countries with increased risk of traveler diarrhea, in cases of suspected immunodeficiency, if sudden onset of symptoms with fever is reported, after antibiotic treatment, and in children below six years of age. As a rule, stool specimens are appropriate, for the detection of cytomegalovirus colonic biopsies are necessary. In the latter case colonosigmoidoscopy has no diagnostic advantage. One single stool specimen is sufficient for the detection of bacteria or toxins, in contrast to parasitological investigations, where only three consecutive specimens provide sufficient diagnostic sensitivity.