Urinary Tract Infections
Heidi L. Smith
I. GENERAL PRINCIPLES
A. Urinary tract infections (UTIs) are the most common nosocomial infections in the United States; most are associated with indwelling urinary catheters.
B. Complications of UTIs requiring intensive care unit (ICU) admission can include pyelonephritis, urosepsis with bacteremia, and suppurative infections.
C. Distinguishing between bacterial or fungal colonization and invasive infection can be difficult in the ICU setting.
II. ETIOLOGY
A. Gram-negative bacteria are most commonly isolated in UTI.
1. Escherichia coli is the most common single cause.
2. Other Enterobacteriaceae (Klebsiella, Citrobacter, Enterobacter, Serratia) are also frequently isolated.
3. Pseudomonas, Providencia, and Proteus sp. are common catheter-associated organisms.
B. Gram-positive bacteria can sometimes cause UTI.
1. Staphylococcus aureus can be seen in the setting of bacteremia; extrarenal sources should be considered.
2. Enterococci (including vancomycin-resistant enterococci [VRE]) and nonaureus staphylococci can be seen in the elderly or in patients with structural abnormalities or indwelling catheters.
C. Candida species can cause UTI and occasionally ascending infection and fungemia.
III. PATHOPHYSIOLOGY
A. Non-catheter-associated UTI.
1. Ascending infection following contamination of the lower tract with enteric organisms from the colon is most common.
2. Virulence factors may aid adhesion (e.g., fimbrial adhesions in E. coli) or alter the urinary tract environment (e.g., urease production by Proteus mirabilis).
3. Host anatomic or functional abnormalities that interfere with normal urine flow or bladder emptying increase risk for UTI.
B. Catheter-associated UTI.
1. Frequent movement in and out of the bladder increases the risk of infection through the external surface of catheter.
2. Risk of infection through the internal lumen increases when a standing column of urine accumulates, collection bag is elevated, or the closed collecting system is disrupted.
3. Temporary obstruction of urine outflow due to kinking aids establishment of pathogens.
IV. DIAGNOSIS
A. Classical clinical presentation consists of dysuria and urinary frequency, with or without fever.
1. Elderly individuals may present only with fever or mental status changes; however, asymptomatic bacteriuria is also very common in the elderly. Caution must be taken to avoid prematurely attributing these symptoms to UTI.
B. Urinalysis aids in the differentiation of microbial colonization versus infection.
1. Urinary white blood cell count >5 cells per high-powered field is suggestive of infection, but is not diagnostic.
2. Chronically catheterized patients, however, may have chronic pyuria in the absence of infection.
