The term urinary tract infection encompasses a variety of clinical entities: cystitis (symptomatic disease of the bladder), pyelonephritis (symptomatic disease of the kidney), prostatitis (symptomatic disease of the prostate), and asymptomatic bacteriuria (ABU). Uncomplicated UTI refers to acute disease in nonpregnant outpatient women without anatomic abnormalities or instrumentation of the urinary tract; complicated UTI refers to all other types of UTI.
UTI occurs far more commonly in females than in males, although obstruction from prostatic hypertrophy causes men >50 years old to have an incidence of UTI comparable to that among women of the same age.
- 50-80% of women have at least one UTI during their lifetime, and 20-30% of women have recurrent episodes.
- Risk factors for acute cystitis include recent use of a diaphragm with spermicide, frequent sexual intercourse, a history of UTI, diabetes mellitus, and incontinence; many of these factors also increase the risk of pyelonephritis.
In the United States, Escherichia coli accounts for 75-90% of cystitis isolates; Staphylococcus saprophyticus for 5-15%; and Klebsiella spp., Proteus spp., Enterococcus spp., Citrobacter spp., and other organisms for 5-10%.
- The spectrum of organisms causing uncomplicated pyelonephritis is similar, with E. coli predominating.
- Gram-positive bacteria (e.g., enterococci and Staphylococcus aureus) and yeasts are also important pathogens in complicated UTI.
In the majority of UTIs, bacteria establish infection by ascending from the urethra to the bladder. Continuing ascent up the ureter to the kidney is the pathway for most renal parenchymal infections.
- The pathogenesis of candiduria is distinct in that the hematogenous route is common.
- The presence of Candida in the urine of a noninstrumented immunocompetent pt implies either genital contamination or potentially widespread visceral dissemination.
When a UTI is suspected, the most important issue is to classify it as ABU; as uncomplicated cystitis, pyelonephritis, or prostatitis; or as complicated UTI.
- Asymptomatic bacteriuria is diagnosed when a screening urine culture performed for a reason unrelated to the genitourinary tract is incidentally found to contain bacteria, but the pt has no local or systemic symptoms referable to the urinary tract.
- Cystitis presents as dysuria, urinary frequency, and urgency; nocturia, hesitancy, suprapubic discomfort, and gross hematuria are often noted as well. Unilateral back or flank pain and fever are signs that the upper urinary tract is involved.
- Pyelonephritis presents as fever, lower-back or costovertebral-angle pain, nausea, and vomiting. Bacteremia develops in 20-30% of cases.
- - Papillary necrosis can occur in pts with obstruction, diabetes, sickle cell disease, or analgesic nephropathy.
- - Emphysematous pyelonephritis is particularly severe, is associated with the production of gas in renal and perinephric tissues, and occurs almost exclusively in diabetic pts.
- - Xanthogranulomatous pyelonephritis occurs when chronic urinary obstruction (often by staghorn calculi), together with chronic infection, leads to suppurative destruction of renal tissue.
- Prostatitis can be either infectious or noninfectious; noninfectious cases are far more common. Acute bacterial prostatitis presents as dysuria, urinary frequency, fever, chills, symptoms of bladder outlet obstruction, and pain in the prostatic, pelvic, or perineal area.
- Complicated UTI presents as symptomatic disease in a man or woman with an anatomic predisposition to infection, with a foreign body in the urinary tract, or with factors predisposing to a delayed response to therapy.
The clinical history itself has a high predictive value in diagnosing uncomplicated cystitis; the likelihood of UTI is 96% in a pt presenting with both dysuria and urinary frequency in the absence of vaginal discharge.
- A urine dipstick test positive for nitrite or leukocyte esterase can confirm the diagnosis of uncomplicated cystitis in pts with a high pretest probability of disease.
- The detection of bacteria in a urine culture is the diagnostic gold standard for UTI. A colony count threshold of >102 bacteria/mL is more sensitive (95%) and specific (85%) than a threshold of 105/mL for the diagnosis of acute cystitis in women with symptoms of cystitis.
Treatment: Urinary Tract Infections
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Women experiencing symptomatic UTIs ≥2 times a year are candidates for prophylaxis—either continuous or postcoital—or pt-initiated therapy. Continuous prophylaxis and postcoital prophylaxis usually entail low doses of TMP-SMX, a fluoroquinolone, or nitrofurantoin. Pt-initiated therapy involves supplying the pt with materials for urine culture and for self-medication with a course of antibiotics at the first symptoms of infection.
In the absence of anatomic abnormalities, recurrent infection in children and adults does not lead to chronic pyelonephritis or to renal failure.
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