The use and abuse of routine stool microbiology: a College of American Pathologists Q-probes study of 601 institutions.

OBJECTIVE: To examine the efficiency with which physicians use routine stool microbiology tests.

DESIGN: Questionnaire and structured review of 100 consecutive stool bacteriology and parasitology examinations at each participating institution.

SETTING: Six hundred one institutions enrolled in the College of American Pathologists Q-probes Program.

RESULTS: Of 59500 bacteriology specimens, 3808 (6.4%) contained a pathogen. The vast majority (99%) of bacterial pathogens were detected in either the first or second specimen submitted. Almost 40% of inpatient specimens were collected after the third day of hospitalization, but only 0.6% of these specimens were positive for enteric pathogens that had not been previously recovered. More than half of the laboratories reported having no limits on the number of bacteriology specimens per patient that could be submitted for testing, and fewer than 8% of laboratories rejected specimens from inpatients after a certain number of days in the hospital. The frequency with which laboratories performed tests for Clostridium difficile varied widely. Of 58500 parasitology specimens, 1463 (2.5%) contained a pathogen; 97.6% of pathogens were detected by the second stool specimen, and 99.8% were detected by the third specimen. Only 0.7% of specimens from inpatients hospitalized more than 4 days contained a new pathogen.

CONCLUSIONS: We recommend that no more than two bacteriology specimens and no more that two or three parasitology specimens be processed per patient without consultation. Standard stool examination for a bacterial pathogens has a low yield and should not be performed after 3 days of hospitalization. Likewise, parasitology examinations should not be performed after 4 days of hospitalization.