New classification of UTIs: From uncomplicated/complicated to localised/systemic
Urinary tract infections (UTIs) are a common reason for seeking medical attention. It is estimated that they account for approximately 1-5% of visits to primary care providers. UTIs have traditionally been classified as either uncomplicated or complicated. The concept of complicated UTIs was first introduced in 1963 and later refined by the Infectious Diseases Society of America (IDSA) and the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) in 1992.
UTIs are considered complicated when they occur in patients with structural or functional abnormalities of the urinary tract, those with compromised immune systems, males, and pregnant women. However, the current definition of complicated UTIs does not encompass the clinical severity, certain risk factors, or pathogen-related characteristics. These parameters can complicate the selection of appropriate antimicrobial therapy, often necessitate longer courses of treatment, and may increase the risk of severe complications such as renal damage or sepsis - all of which are key considerations in defining a complicated UTI.
New classification
The EAU Guidelines Panel on Urological Infections has extensively discussed this issue and proposed modifications to the definitions of uncomplicated and complicated UTIs to reduce misinterpretation and improve clinical decision-making. Two main considerations have emerged: (1) the clinical condition of the patient should be taken into account, and (2) individual patient risk profiles should be systematically assessed.
The ORENUC classification system, first proposed in 2011, could be a useful tool for stratifying risk, particularly in patients with recurrent UTIs. ORENUC is an acronym that categorises patients into six groups:
- O – No known risk factors
- R – Risk factors for recurrent UTIs
- E – Extra-urogenital risk factors
- N – Nephropathy
- U – Urological risk factors that can be resolved with therapy
- C – Catheter-related risk factors
Based on clinical signs and symptoms, the EAU Guidelines Panel has also proposed a classification of UTIs into ’localised’ and ‘systemic’:
- Localised UTI: Cystitis without signs or symptoms of systemic infection in either sex. Common symptoms include dysuria, urinary frequency, urgency, and suprapubic pain.
- Systemic UTI: A UTI accompanied by signs or symptoms of systemic infection, with or without localised urinary symptoms, in either sex. Systemic features may include fever or hypothermia, rigors, chills, delirium, hypotension, tachycardia, and costovertebral angle tenderness.
Both localised and systemic UTIs may be associated with risk factors that predispose patients to a more complicated clinical course. These include:
- Paediatric or geriatric (frail) patients
- Anatomical or functional abnormalities of the urinary tract
- Indwelling urinary catheters
- Urolithiasis (urinary stones)
- Immunocompromised states
- Significant post-void residual urine volume
- Neurological disorders
- Recent antibiotic use
- History of multidrug-resistant pathogens
- Urinary tract obstruction
- Recent urinary tract instrumentation
- Prostatic involvement
- Pregnancy
- Pelvic organ prolapse
According to the current proposed definitions, localised infections may often be managed in an outpatient setting, including males and patients with risk factors. In contrast, systemic UTIs typically require intravenous antibiotic therapy and a more comprehensive diagnostic work-up, including blood cultures and imaging studies.