Urinary Tract Infection
Virginia P. Arcangelo
Urinary tract infection (UTI) is a broad term used to describe inflammation of the urethra, bladder, and kidney. Bacteria, yeast, or chemical irritants can cause inflammation in the urinary tract. UTIs are a common problem encountered in health care. It is estimated that each year, there are at least 150 million cases of symptomatic UTIs worldwide (Foxman, 2014). UTIs occur across the life span. As many as 10% of women experience at least one episode of acute uncomplicated urinary infection in a year, and 60% have at least one episode during their lifetime. The peak incidence of infection occurs in young, sexually active women ages 18 to 24. Recurrent episodes are experienced by as many as 5% of women at some time during their life.
The clinical spectrum of UTIs ranges from asymptomatic bacteriuria, to symptomatic and recurrent UTIs, to sepsis associated with UTI requiring hospitalization. Recent evidence helps differentiate asymptomatic bacteriuria from symptomatic UTI. Asymptomatic bacteriuria is transient in older women, often resolves without any treatment, and is not associated with morbidity or mortality. The diagnosis of symptomatic UTI is made when a patient has both clinical features and laboratory evidence of a urinary infection. Absent other causes, patients presenting with any two of the following meet the clinical diagnostic criteria for symptomatic UTI: fever, worsened urinary urgency or frequency, acute dysuria, suprapubic tenderness, or costovertebral angle pain or tenderness. A positive urine culture (≥105 CFU/mL) with no more than two uropathogens and pyuria confirms the diagnosis of UTI. Risk factors for recurrent symptomatic UTI include diabetes, functional disability, recent sexual intercourse, prior history of urogynecologic surgery, urinary retention, and urinary incontinence. Testing for UTI is easily performed in the clinic using dipstick tests.
Women contract UTIs in a 30:1 ratio to men because of their short urethra and its proximity to the rectum. Sexual intercourse is a contributing factor. With intercourse, periurethral and urethral bacteria may ascend into the bladder. After age 65, the ratio of UTIs in women to men becomes closer to 1. Risk factors for UTIs in men include homosexuality, intercourse with an infected partner, and an uncircumcised penis.
Normal urine is sterile. Infection occurs when microorganisms, usually bacteria from the digestive tract, cling to the opening of the urethra and multiply. Escherichia coli is the causative pathogen in 85% to 90% of community-acquired UTIs. Staphylococcus saprophyticus accounts for approximately 5% to 15% of UTIs in young women. The microbial spectrum of complicated UTIs is broader and also includes Pseudomonas, Enterococcus, Staphylococcus, Serratia, Providencia, and fungi.
Bacterial growth is decreased by dilute urine and a low urine pH. Glucose in urine is an enhanced medium for the growth of E. coli. The urine from pregnant women has a more suitable pH for growth of E. coli. Diaphragm and spermicide use (nonoxynol 9), estrogen deficiency, and constipation also are risk factors for UTIs. Inefficient bladder emptying causes UTIs because of stagnating urine. Underlying conditions that predispose to UTI are listed in Box 32.1.