Context: The yield of in-hospital stool cultures performed more than 72 hours after admission is low, and a commonly used policy dictates that laboratories reject these cultures to save costs. However, enteropathogenic bacteria other than Clostridium difficile (EPB) may cause nosocomial illness that would be missed by use of such a "3-day rule."
Objective: To develop guidelines for hospital use of stool cultures that are sensitive to clinically relevant cases of sporadic and epidemic nosocomial diarrhea.
Design: Five-part study that incorporated a derivation sample based on retrospective chart review and a prospective cohort study (including cost savings analysis), and a validation sample based on retrospective chart review.
Setting: Four European academic health care centers.
Patients: Derivation sample: 1735 adult inpatients from whom 3416 stool cultures were obtained during a 19-month period (1995-1997) and 68 adult inpatients for whom EPB were grown from stool cultures during a 10-year period (1988-1998); validation sample: 65 patients with sporadic isolation of EPB (1993-1998), 56 patients involved in 2 nosocomial Salmonella outbreaks (1992 and 1997), and 330 patients who had stool cultures performed (1998).
Main outcome measure: Performance of derived criteria in detecting pathogenic bacteria and outbreaks and reducing total number of stool cultures performed.
Results: Stool cultures grew EPB in 3.3% of samples obtained </=72 hours after admission and 0.5% of samples obtained thereafter (P<.001). Isolation of EPB >72 hours after admission was not associated with clinical symptoms or signs but was associated with community-acquired diarrhea (24%), age 65 years or older with preexisting comorbid disease (25%), neutropenia (13%), HIV infection (10%), and nondiarrheal manifestations of enteric infections (16%). Twelve percent were asymptomatic carriers. These characteristics were used to create criteria for selecting patients for whom stool cultures would be indicated. These criteria were applied post hoc to a series of 1025 stool cultures; the number of stool cultures would have been reduced by 52% and no clinically significant cases would have been missed. Annual savings to a 355-bed institution would be approximately $7800 for reagent costs and 75 hours of technician time. In the validation samples, only 2 patients of 65 who had EPB would not have been identified, and neither required treatment. If the 3-day rule had been applied, 52 cases would not have been identified, 28 of which required antibiotic treatment.
Conclusion: Our modified 3-day rule for use in selecting cases for stool culture is sensitive to sporadic and epidemic cases of nosocomial diarrhea in hospitalized adults.