A urinary tract infection (UTI) is an infection that affects any part of the urinary system, including the urethra, bladder, ureters, or kidneys. Most UTIs are caused by bacteria, commonly Escherichia coli, entering the urinary tract and multiplying. Symptoms often include a frequent or urgent need to urinate, burning or pain during urination, cloudy or strong-smelling urine, lower abdominal discomfort, and sometimes blood in the urine. Infections affecting the kidneys may cause additional symptoms such as back or flank pain, fever, chills, and nausea. UTIs can occur in anyone but are more common in women due to anatomical differences in the urinary tract. Prompt evaluation is important to prevent the infection from spreading to the kidneys or bloodstream.