Laboratory diagnosis of infectious diarrhea

The microbiology laboratory, in conjunction with the medical staff, must determine a reasonable approach to the evaluation of diarrheal stools since the cost to rule out all potential pathogens is prohibitive and control of the use of laboratory services is now a major focus in all institutions. All stool cultures should be examined for Campylobacter, Salmonella, and Shigella, the most common causes of inflammatory bacterial diarrhea in the United States. Special media for other pathogens should be added only if there is high regional endemicity or significant clinical suspicion. If a child has bloody diarrhea, a search for E coli O157:H7 is indicated. For patients with a history of raw seafood ingestion or foreign travel, the laboratory should be asked to screen specimens for Vibrio and Plesiomonas species. The report from the laboratory should specifically state what enteropathogens have been excluded, for example, "No Salmonella, Shigella, or Campylobacter isolated." A report of "negative" or "no enteric pathogens" is not very useful. Diagnosis of viral and parasitic enteritis and antibiotic-associated diarrhea require a variety of additional tests. Clinicians are encouraged to discuss these issues with the pathologist or microbiologist at their local laboratory and be familiar with community microbiology practice, particularly which organisms require a special request for the laboratory to attempt identification.