New Technique for Urine Culture Improves Pathogen Detection in UTI

A new enhanced technique for urine culture, known as the enhanced quantitative urine culture (EQUC) protocol, detected significantly more pathogens than standard urine culture in women with symptoms of urinary tract infection (UTI). These study results were presented at American Society for Microbiology (ASM) Microbe 2017, held June 1-5 in New Orleans, Louisiana.¹

The standard urine culture was originally used to identify patients at increased risk of pyelonephritis. For the last few decades, its use has been expanded to detecting UTIs with a cutoff of ≥10⁵  colony-forming units (CFU)/mL of a known uropathogen. While the standard urine culture is the gold standard for diagnosing UTI, data suggest that bacteria are present in approximately 90% of standard urine cultures with no bacterial growth.²

Previously, the EQUC protocol was shown to achieve higher uropathogen detection rates than the standard urine culture (84% vs 33%).² Researchers, led by Travis Price, MS, and Elizabeth Mueller, MD, from Stritch School of Medicine, Loyola University in Chicago, Illinois, sought to identify the optimal urine culture protocol for diagnosing UTI, the urinary symptoms most strongly associated with UTI, and the CFU threshold for diagnosing UTI.¹

Women enrolled in the study (n=150) answered “yes” or “no” to the question, “Do you feel you have a UTI?” with 75 in the “yes” group and 75 in the “no” group. Urine samples from the participants were cultured using standard urine culture, expanded EQUC, and streamlined EQUC protocols.¹

Expanded EQUC protocols may use higher volumes of urine (1, 10, or 100 µL) and different growth media than the standard protocol (urine volume = 1 µL). The streamlined EQUC protocol was developed from the most optimal expanded EQUC protocol in order to provide comprehensive detection of uropathogens. The streamlined EQUC protocol requires 100 µL of urine and incubates samples in 3 growth media (blood, CNA, and MacConkey) in 5% carbon dioxide (CO₂) for 48 hours.¹

In the “yes” group, only half of uropathogens were detected by standard urine culture, compared with 91% by streamlined EQUC.¹

While standard urine culture was highly sensitive for detecting Escherichia coli (detection rate, 88%), it performed poorly for detecting non-E coli pathogens (detection rate, 12%).¹

Detectable uropathogens (≥10 CFU/mL) were present in urine samples from 69 women in the “yes” group. Of these, 67% had one or more pathogens with a concentration of ≥10⁵ CFU/mL, the majority of which were Gram-negative. However, using lower thresholds revealed that other microbes, such as Gram-positive bacteria, accounted for up 62% of pathogens. UTI symptoms improved in most patients with ≥1 pathogen present at ≥10⁵ CFU/mL who were treated with antibiotics, but remained unchanged or worsened in 60% of patients with pathogens present at <10⁵ CFU/mL who were not treated.¹

Participants also reported their symptoms with the UTI Symptoms Assessment (UTISA) questionnaire. “Urinary urgency and urinary frequency are not symptoms that are specific for UTIs,” Dr Mueller told Infectious Disease Advisor. “The ‘best’ symptom is dysuria or pain with urination.”

The EQUC protocols may detect more pathogens than standard urine culture, but their utility in the clinical setting has not been established. Dr Mueller indicated that she and her colleagues are developing a clinical trial to determine whether using EQUC protocols to diagnose UTI in women who feel they have a UTI leads to improved symptoms. 

References

1. Price TK, Dune T, Hilt EE, et al. Detecting clinically relevant microorganisms: we can do better. Presented at: ASM Microbe 2017; New Orleans, LA; June 1-5. Session 206-CPHM03. Poster 459.
2. Price TK, Dune T, Hilt EE, et al. The clinical urine culture: enhanced techniques improve detection of clinically relevant microorganisms. J Clin Microbiol. 2016;54(5):1216-1222. doi:10.1128/JCM.00044-16