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URINARY TRACT INFECTIONS

Definitions

The term urinary tract infection (UTI) 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.

Epidemiology

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.

Microbiology

In the United States, Escherichia coli accounts for 75–90% of cystitis isolates; Staphylococcus saprophyticus for 5–15%; and Klebsiella species, Proteus species, Enterococcus species, Citrobacter species, 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.

Pathogenesis

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.

Clinical Manifestations

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 with 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 with 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 ...

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