What is the most recent evidence-based classification of urinary tract infections (UTIs) in regards to complicated vs uncomplicated infections?

Evidence-Based Classification of UTIs: Complicated vs Uncomplicated

The 2024 European Association of Urology guidelines classify UTIs into uncomplicated and complicated categories based on host factors and anatomical/functional abnormalities, with the fundamental principle that complicated UTIs carry higher risks of recurrence, progression, and severe outcomes including mortality. 1

Uncomplicated UTI Definition

Uncomplicated UTIs are strictly limited to acute, sporadic, or recurrent cystitis in nonpregnant women without:

• Relevant anatomical or functional abnormalities in the urinary tract 1
• Comorbidities that increase infection risk 1
• Signs of tissue invasion or systemic infection 1

This narrow definition means that even repeated pyelonephritis should prompt consideration of a complicated etiology 1.

Complicated UTI Definition

A complicated UTI occurs when host-related factors or specific anatomical/functional abnormalities make the infection more challenging to eradicate compared to uncomplicated infection. 1

Host-Related Complicating Factors

The 2024 EAU guidelines specify the following as complicating factors 1:

Patient Demographics:

• Male gender (all UTIs in males are considered complicated) 1, 2
• Pregnancy 1

Medical Comorbidities:

• Diabetes mellitus 1
• Immunosuppression 1

Healthcare-Associated Factors:

• Recent history of instrumentation 1
• Health care–associated infections 1
• Catheterization (current or within past 48 hours) 1

Anatomical/Functional Complicating Factors

Structural Abnormalities: 1

• Obstruction at any site in the urinary tract
• Foreign body presence
• Vesicoureteral reflux
• Incomplete voiding
• Bladder or urethral diverticula
• Fistulae

Microbiological Complicating Factors

The 2024 guidelines now emphasize multidrug-resistant organisms as a key complicating factor: 1

• ESBL-producing organisms isolated
• Multidrug-resistant organisms isolated

This represents an important evolution in classification, recognizing that antimicrobial resistance patterns directly impact infection complexity and outcomes 1.

Clinical Implications of Classification

The distinction between complicated and uncomplicated UTIs has direct implications for:

Microbial Spectrum:

• Uncomplicated UTIs are predominantly caused by E. coli 1
• Complicated UTIs have a broader spectrum including E. coli, Proteus spp., Klebsiella spp., Pseudomonas spp., Serratia spp., and Enterococcus spp. 1

Antimicrobial Resistance:

• Antimicrobial resistance is significantly more likely in complicated UTIs 1
• This necessitates urine culture and susceptibility testing before treatment 1

Treatment Duration:

• Uncomplicated cystitis: short-course therapy (3-7 days depending on agent) 1
• Complicated UTIs: 7-14 days minimum (14 days for men when prostatitis cannot be excluded) 1

Management Approach:

• Uncomplicated UTIs can often be diagnosed clinically without routine urine culture 1
• Complicated UTIs require mandatory urine culture and susceptibility testing 1
• Complicated UTIs require addressing the underlying anatomical or functional abnormality 1

Common Pitfalls to Avoid

Do not classify the following as uncomplicated UTIs, even if they seem straightforward: 1

• Any UTI in a male patient
• Recurrent pyelonephritis (even in otherwise healthy women)
• UTIs in pregnant women
• UTIs in diabetic patients

Do not use short-course therapy (≤3 days) for complicated UTIs, as this leads to treatment failure and does not adequately address the higher bacterial burden and resistance patterns 1, 2.