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EPIDEMIOLOGY

Key Clinical Questions

  • image Which patients with urinary tract infection (UTI) need hospital admission?

  • image When should catheter-associated UTI be treated?

  • image When is renal imaging indicated?

  • image When should urology consultation be obtained?

  • image What are the appropriate durations of therapy for uncomplicated cystitis, catheter-associated UTI, and pyelonephritis?

  • image For which patients are follow-up urine cultures indicated after discharge?

Over half of all women have at least one urinary tract infection (UTI) during their lifetime. In the United States, community-acquired UTIs lead to 7 million office visits, 1 million emergency room visits, over 100,000 hospitalizations, and costs of over $1.6 billion annually. The most common nosocomial infection is catheter-associated UTI, with over 1 million cases yearly in the United States alone.

The vast majority of UTIs arise by the ascending route. Most are caused by strains of Escherichia coli with surface filaments (fimbriae) that stick to urinary epithelium. UTIs occasionally arise from bacteremia. This is especially true of Staphylococcus aureus. While S. aureus may cause cystitis in patients with Foley catheters, when patients present with staphylococcal pyelonephritis from the community, beware of the possibility of underlying bacteremia and endocarditis.

Cystitis and pyelonephritis are 5 to 10 times more common in women, due to the short-female urethra. In women under the age of 50 years, the major risk factor for UTI is frequency of sexual intercourse, which facilitates passage of bacteria into the bladder. In healthy women, UTIs are also associated with new sexual partners, reflecting sexual acquisition of uropathogenic strains of E. coli, and use of spermicides, which promote periurethral E. coli colonization.

The normal urinary tract has robust anatomical, chemical, and immunological defenses against infection. These are all negated by the placement of an indwelling urinary catheter, which allows bacteria to migrate upward along the external and internal catheter surfaces. The rate of acquisition of bacteriuria after placement of a urinary catheter is 5% per day. Essentially 100% of patients have bacteriuria 1 month after placement of an indwelling urinary catheter. Other host abnormalities that predispose to UTI include diabetes mellitus and glucosuria, urinary stasis from obstruction, bladder diverticula, neurologic disease, vesicoureteral reflux, and urinary calculi (Figure 197-1), which may cause local irritation, obstruction, and serve as a nidus for persistent infection.

Figure 197-1

CT scan of the abdomen, showing pyelonephritis in a patient with urinary tract obstruction from a stone at the ureteropelvic junction. The right kidney is significantly enlarged, with hydronephrosis and perinephric fat stranding.

RISK STRATIFICATION

Patients with uncomplicated cystitis or infection limited to the urinary bladder do not require hospital admission unless there are other medical concerns, such as confusion, dehydration, and inability to take oral antibiotics. Reliable patients with kidney infection or pyelonephritis with mild illness, good oral intake, and anatomically normal urinary ...

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