Bacterial and Protozoal Gastroenteritis

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Abstract
Guerrant and Bobak (Aug. 1 issue)1 point out that the cost of routine stool cultures is very high and suggest a selective approach to help improve the cost effectiveness of cultures. A major reason for the high cost of stool cultures that is not discussed is the failure to consider different diagnostic approaches to nosocomial as opposed to community-acquired diarrhea. Although most clinicians would agree that hospitalized patients rarely if ever acquire salmonellosis, shigellosis, campylobacteriosis, or amebiasis during their hospitalization, routine stool cultures and parasitologic examinations are regularly ordered for hospitalized patients with diarrheal disease. Studies at our institution showed that although 50 percent of the stool specimens submitted for routine workup were obtained from the inpatient population (i.e., more than three days after admission), only 1 of 191 positive routine cultures (for campylobacter, salmonella, or shigella species) and none of the 90 cultures positive for ova and parasites over a three-year period were obtained from this population.2 However, about 25 percent of stool specimens submitted for the detection of Clostridium difficile toxin were positive, regardless of the patient's admission status. The single patient with diarrhea due to salmonella was known to have been been exposed in the community. Although selective culturing based on clinical findings may be helpful in improving the cost effectiveness of stool examinations for infectious agents, preselecting patients according to their admission status and thus their pretest probability of having a community-acquired stool pathogen would have an equal if not a greater impact on the cost effectiveness of stool examinations.