Yield of Stool Cultures and Prevalence of Pathogens at a safety net hospital

From the 2018 HVPAA National Conference

Jessica Barnes (University of Texas Southwestern Medical Center, Dallas, TX;), Kadam Patel (University of North Texas Health Sciences Center), Paul Southern (University of Texas Southwestern Medical Center, Dallas, TX;), Deepak Agrawal (University Texas Southwestern Medical Center)

Background

Reflex ordering of stool studies including stool cultures, and ova and parasites are commonly performed in the emergency department and hospital setting, for workup of diarrhea, with variable reported yields. Prior studies have shown the diagnostic yield of this test is maximized if performed within 72 hours of hospital admission.

Objectives

To evaluate the diagnostic yield of stool cultures and examine the prevalence of pathogens at a large, safety-net, county hospital.

Methods

Retrospective analysis of stool cultures performed on patients in the emergency room or as inpatients at a county hospital from December 2011 to February 2017. The frequency of positive results was evaluated. Subgroup analysis was performed based on timing of testing (greater or less than 72 hours since admission). The prevalence of specific pathogens was calculated among all positive samples.  Cost data for stool cultures was estimated to be $40 per sample based on Medicare reimbursement rates.

Results

The overall yield of stool cultures was 3.6% (312 out of 8,625 studies performed). 7,670 samples were sent within 72 hours of admission and 955 were sent after 72 hours.  The yield of stool cultures after 72 hours of admission decreased to 0.6% (6 positive samples). Of these 6 patients – 2 patients were HIV positive, 2 had salmonella bacteremia and in 2 patients the positive findings were ignored and patients not treated.  The prevalence of pathogens found are provided in Table 1.  Stool cultures were estimated to cost $69,000 annually, which equates to $221 per positive sample. Limiting samples to within 72 hours of admission could save an estimated $7,640 annually.

Conclusion

The yield of routine testing of stool cultures at a large county hospital is very low especially after 72 hours of admission. Restricting checking stool cultures only to patients within 72 hours, except specific cases, is the most cost-effective approach.

Implications for the Patient

Establishing criteria of checking stool cultures only if checked within 72 hours of admission can result in significant cost savings without impacting patient care.