Urinary tract infection (UTI)

A urinary tract infection (UTI) is an infection anywhere along the urinary system — urethra, bladder, ureters, or kidneys. Lower UTIs include urethritis and cystitis (bladder infection), the most common form; an upper UTI, or pyelonephritis, involves the kidney and is more serious. Most infections are ascending: bacteria from the perineum travel up the urethra into the bladder, and sometimes onward to the kidneys.

Uropathogenic Escherichia coli causes the large majority of cases, with organisms like Staphylococcus saprophyticus (classically in young women), Klebsiella, Proteus, and Enterococcus accounting for most of the rest. Women are affected far more often than men because the female urethra is shorter and closer to the anus. Other risk factors include sexual activity, urinary catheters, urinary obstruction or stones, pregnancy, and diabetes.

Cystitis presents with dysuria (painful urination), frequency, urgency, and suprapubic discomfort; pyelonephritis adds fever, flank pain, costovertebral angle tenderness, and often nausea. Diagnosis relies on urinalysis — positive leukocyte esterase, nitrites (from nitrate-reducing organisms like E. coli), white cells, and bacteria — confirmed by urine culture. Untreated upper infections can progress to renal scarring or urosepsis, so recognition matters.

UTIs are tested widely across health-professions exams. The USMLE Step 1 emphasizes the causative organisms and urinalysis findings, the CCMA covers UTIs among urinary system diseases and specimen collection, and the NCLEX tests UTI recognition and prevention in nursing care contexts such as postpartum patients, where urinary retention and catheterization raise risk.