Derivation and validation of guidelines for stool cultures for enteropathogenic bacteria other than Clostridium difficile in hospitalized adults

Context The yield of in-hospital stool cultures performed more than 72 hour s after admission is low, and a commonly used policy dictates that laborato ries reject these cultures to save costs. However, enteropathogenic bacteri a 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 retro spective chart review and a prospective cohort study (including cost saving s 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 cult ures were obtained during a 19-month period (1995-1997) and 68 adult inpati ents for whom EPB were grown from stool cultures during a 10-year period (1 988-1998); validation sample: 65 patients with sporadic isolation of EPB (1 993-1998), 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 pathogeni c bacteria and outbreaks and reducing total number of stool cultures perfor med. Results Stool cultures grew EPB in 3.3% of samples obtained less than or eq ual to 72 hours after admission and 0.5% of samples obtained thereafter (P< .001). Isolation of EPB >72 hours after admission was not associated with c linical symptoms or signs but was associated with community-acquired diarrh ea (24%), age 65 years or older with pre existing comorbid disease (25%), n eutropenia (13%), HIV infection (10%), and nondiarrheal manifestations of e nteric infections (16%). Twelve percent were asymptomatic carriers. These c haracteristics 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 b een reduced by 52% and no clinically significant cases would have been miss ed. Annual savings to a 355-bed institution would be approximately $7800 fo r 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 neit her 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 cul ture is sensitive to sporadic and epidemic cases of nosocomial diarrhea in hospitalized adults.