Urinary tract infections (UTIs) are one of the most common bacterial infections in both community and healthcare settings, leading to frequent antibiotic use. They range widely in severity, from mild cases like cystitis to severe, potentially life-threatening conditions such as pyelonephritis, bacteraemia, and septic shock. Historically, UTIs have been categorised as either uncomplicated or complicated. Uncomplicated UTIs typically occur in healthy, non-pregnant women, while all other UTIs are considered complicated. However, this classification has limitations. For example, a woman with high-grade fever and pyelonephritis could be classified as having an uncomplicated UTI, potentially leading to inadequate treatment, whereas a man with mild cystitis would be categorised as complicated, possibly resulting in overtreatment with broad-spectrum antibiotics. The original classification of uncomplicated and complicated UTIs was established in 1992 by the Infectious Diseases Society of America and the European Society of Clinical Microbiology and Infectious Diseases. It was designed to standardise study cohorts in clinical trials for new anti-infective drugs. At that time, complicated UTIs were associated with catheter use or anatomical abnormalities of the urinary tract. Over time, the recognition of risk factors like age, immunosuppression, and diabetes has refined treatment approaches, though the basic classification remains tied to these predisposing conditions rather than the presence of systemic infection. In recent years, definitions of complicated UTIs have expanded. The 2018 US Food and Drug Administration (FDA) guidelines define complicated UTIs as infections with both local and systemic symptoms, particularly in patients with urinary tract abnormalities or catheters. Under these guidelines, pyelonephritis is now considered a form of complicated UTI, making the term “uncomplicated pyelonephritis” obsolete. However, variations in the definitions used across studies create challenges in interpreting results, highlighting the need for a more practical approach in clinical care. To address these challenges, a modified classification system for UTIs is proposed. This new framework retains the terms “uncomplicated” and “complicated” but emphasises the clinical presentation, distinguishing between localised (uncomplicated) and systemic (complicated) infections. This classification also encourages consideration of sex-specific factors, reflecting new knowledge of genetic and microbiome differences between men and women. Biological sex influences immune responses to infections, particularly those affecting mucosal surfaces like the bladder. By adopting this updated classification, clinicians can better tailor UTI management to individual patients, factoring in sex-specific nuances and risk factors such as urinary catheters, neurological conditions, and urinary obstructions. This approach provides a clearer framework for diagnosing and treating UTIs, ensuring more effective and personalised care.
