Impact of Pre-Existing Urinary Antimicrobial Agents on Culture Yield, Diagnostic Accuracy, and the Detection of Significant Bacteriuria in Community-Acquired Urinary Tract Infections.

INTRODUCTION: Pre-existing antibacterial substances (ABS) in urine can significantly impact the diagnostic and therapeutic management of urinary tract infections (UTIs) by altering microbial culture outcomes and influencing the detection and resistance profiles of uropathogens. The presence of pre-existing ABS may lead to false-negative or insignificant culture results, affecting clinical decision-making. This study aims to assess the impact of pre-existing ABS on culture positivity, microbial distribution, and antibiotic susceptibility patterns in outpatients, particularly those with prior antimicrobial exposure.

METHODS: A prospective observational study was conducted at a tertiary care hospital on 621 outpatients with clinical symptoms suggestive of UTI. Urine samples were analyzed for pre-existing ABS and classified into pre-existing ABS-positive (n = 158) and pre-existing ABS-negative (n = 463) groups. Data on demographics, clinical characteristics, comorbidities, and microbiological profiles were collected. Associations between pre-existing ABS presence and variables such as prior antibiotic exposure, requisition form completeness, and diabetes mellitus were evaluated using chi-square tests. A p-value of <0.05 was considered statistically significant.

RESULTS: The study population comprised 356 females (57.32%), with a mean age of 30.68 years. The most common presenting symptom was an increased urinary frequency (76.16%), followed by abdominal pain (62.47%). Pre-existing ABS were detected in 158 (25.44%) cases. Significant associations were observed between pre-existing ABS presence and prior antibiotic use (χ² = 31.61 p < 1.88 × 10 ⁻⁸,), adequate requisition form documentation (χ² (df) = 40.58, p < 1.88 × 10 ⁻¹⁰), and diabetes mellitus (χ² (df) = 9.02, p = 0.0027). Culture positivity was significantly reduced in pre-existing ABS-positive samples, with lower isolation rates of Escherichia coli (27.21% vs. 39.52%, p = 0.007) and an increased prevalence of Proteus mirabilis (10.75% vs. 4.96%, p = 0.018). Pre-existing ABS-positive samples also showed significantly higher rates of no growth (17.49% vs. 9.49%, p = 0.023) and insignificant growth (19.62% vs. 12.00%, p = 0.026). Antibiotic susceptibility analysis revealed that pre-existing ABS-positive isolates of E. coli and Klebsiella pneumoniae exhibited reduced susceptibility to amoxicillin-clavulanic acid, cefazolin, and imipenem compared to pre-existing ABS-negative isolates, suggesting a potential impact of prior antimicrobial exposure on resistance patterns.

CONCLUSION: The presence of pre-existing ABS in urine significantly alters microbial culture outcomes, leading to reduced detection of common uropathogens and an increased likelihood of false-negative or insignificant culture results. Additionally, pre-existing ABS-positive isolates demonstrate higher resistance to key antibiotics, highlighting the need for careful interpretation of urine culture results in patients with prior antimicrobial exposure. Comprehensive documentation of antibiotic history and requisition form completeness is essential to improve diagnostic accuracy. Further research is warranted to explore the role of pre-existing ABS in promoting antimicrobial resistance in community-acquired UTIs and to refine diagnostic criteria for significant bacteriuria in the presence of pre-existing ABS.