PP16 -Screening urine cultures for presence of antibiotics – Internal quality audit in a base hospital in Sri Lanka

Abstract

Introduction

Urine culture is a crucial test for determining the etiology of urinary tract infections (UTIs). The presence of antibiotics in urine can reduce the bacterial load in positive urine cultures, leading to an inaccurate interpretation.

Objectives

This study was conducted to determine the prevalence of unreported antibiotic use prior to urine culture and its effect on the culture reports.

Design, setting, and methods

The study was conducted over a two-week period, using both inpatient and clinic urine samples.

The urine anti-bacterial substance assay (UABA) described in the literature was performed for each sample using Mueller-Hinton agar plates inoculated with a lawn of Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923. The presence of an inhibition zone was taken as a positive UABA test. Urine cultures were performed according to the standard operating procedure.  Details on the request forms and the culture results were compared with the study's findings.

Results

Out of the total 92 samples, 60 (65.2%) were positive for UABA, indicating the presence of antibiotics.  Among these UABA-positive samples, 85% (51/60) showed no growth in the urine culture, while 3.3% (2/60) showed ‘no significant growth’. Among UABA negative samples, 62.5% (20/32) showed no growth in the urine culture. Fisher’s exact test gave a p-value of 0.039, indicating a significant association between UABA test results and culture outcomes.

Out of UABA-positive samples, 80% (48/60) had clinical details provided, but only 51.6% (31/60) included clinical history suggestive of UTI in the request forms. Antibiotic usage was mentioned only in 21.7% (13/60) of the request forms. In UABA-negative samples, 53.1% (17/32) included clinical history, and 46.8% (15/32) had UTI-suggestive history in the request forms.

Conclusion

The majority of urine samples showed the presence of antibiotics; however, the documentation on the request form was inadequate. The presence of antibiotics has significantly impacted the culture results, resulting in increased reports of 'no growth' and 'no significant growth.' Periodic auditing of the presence of antibiotics in urine can serve as a method to enhance laboratory quality.