Chapter 205. Urinary Tract Infections and Pyelonephritis

1. Which patients with urinary tract infections need hospital admission?

2. When should catheter-associated urinary tract infections be treated?

3. When is renal imaging indicated?

4. When should urology consultation be obtained?

5. What are the appropriate durations of therapy for uncomplicated cystitis, catheter-associated urinary tract infections, and pyelonephritis?

6. For which patients are follow-up urine cultures indicated after discharge?

Urinary tract infections are very common, and account for a significant portion of health care costs. 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 seven million office visits, one 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 one 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 bind to urinary epithelium. UTIs occasionally arise from bacteremia. This is especially true of Staphylococcus aureus. Whereas 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 otherwise healthy women, UTIs are also associated with new sexual partners, reflecting sexual acquisition of uropathogenic strains of E coli, spermicide use, which allows periurethral E coli colonization, and probably genetic factors.

The normal urinary tract has robust anatomic, chemical, and immunologic defenses against infection. These are all negated by the placement of an indwelling urinary catheter. The rate of acquisition of bacteriuria after placement of a urinary catheter is 5% per day. Essentially 100% of patients have bacteriuria one month after placement of an indwelling urinary catheter. Other host abnormalities that predispose to UTI are diabetes mellitus and glucosuria, urinary stasis from obstruction, bladder diverticula, neurologic disease, vesicoureteral reflux, and urinary calculi (Figure 205-1), which may cause local irritation or obstruction and serve as a nidus for persistent infection.

Asymptomatic Bacteriuria

Asymptomatic bacteriuria is very common. It is found in 5% of healthy women, 50% of elderly patients in long-term care facilities, and in most patients with spinal cord injury. Rates of bacteriuria are essentially 100% in patients with chronic indwelling Foley catheters or permanent ureteric stents.