Urinary tract infections (UTIs) are the most common infections identified in both outpatient and inpatient settings. UTIs occur in patients of all ages, affecting females throughout life and males at each end of the age spectrum. They represent approximately 8.6 million visits in the ambulatory setting and are the most commonly diagnosed healthcare-associated infection. The term urinary tract infection encompasses a group of conditions that includes cystitis, pyelonephritis, and asymptomatic bacteriuria. Appropriate management of a patient with a UTI requires consideration of multiple factors, including age, sex, underlying comorbidities, pregnancy, history of prior UTIs, location of infection, and the pathogen involved.

Determination of the location of the infection as upper versus lower tract is essential to selection of optimal therapy. Lower urinary tract infection is infection involving the bladder, or cystitis, and is characterized by dysuria, pyuria, urinary frequency, or urinary urgency. Upper urinary tract infection, or pyelonephritis, is infection involving the bladder and kidney that classically presents with fever and flank pain, with or without the symptoms of lower tract infection.

Differentiating uncomplicated from complicated UTI is also critical to developing an appropriate treatment strategy. An uncomplicated UTI is an infection occurring in an otherwise healthy individual who has no functional or structural abnormalities of the kidneys, ureters, bladder, or urethra. Most adult women with cystitis fall into this category. Complicated UTIs are those infections occurring in the setting of functional or anatomic abnormalities of the upper or lower tract (such as urinary retention from anatomic obstruction or neurogenic bladder and nephrolithiasis), in the presence of an indwelling bladder catheter, or in patients with underlying conditions such as pregnancy, diabetes mellitus, or renal transplantation.