Urinary Tract Infections

UTIs account for 30% of all nosocomial infections [NEJM 329: 1328, 1993], with catheterization being the most important predisposing factor (4 – 7% risk per day [Am J Med 92S4A: 114, 1992]). The key pathogenic event is loss of Lactobacillus protection. Diagnosis cannot be based on cultures alone because half of all patients with catheters will have positive cultures at 5 days and 95% of catheterized patients will have positive cultures at 30 days [Crit Care Med 33: 1538, 2005] – the diagnosis REQUIRES a symptom/sign of infection (note that 50% of elderly will present with altered mental status AMS [J Crit Illness 11S: 30, 1996]). Cultures are positive if 105 CFU/mL (or 102 CFU/mL x 2 separate days).

Microbial Isolates in Nosocomial UTIs

Microorganism Frequency Escherichia coli 36% Enterococcus spp. 33% Pseduomonas aeruginosa 13% Klebsiella pneumoniae 12% Proteus mirabilis 7% Candida albicans 4% Staphylococcus epidermidis 4% Staphylococcus aureus 4%

Clin Microbiol Rev 6: 428, 2003

Diagnosis is complicated by the baseline pyuria and/or bacteriuria often found in chronically catheterized patients. Microscopy criteria (> 10 WBC/HPF and > 2 bacteria/oil-immersion field) were designed for outpatient use. Also, urine cultures can be misleading and often take too long.

Candida usually represents colonization of the lower urinary tract, but can also represent disseminated candidiasis with renal involvement (look for fever, leukocytosis, septic picture to distinguish, do not rely on urine colony counts. Also, blood cultures may be sterile in up to 50% of cases [Intensive Care Med 20: 522, 1994]). Therapy is unnecessary unless fever, abdominal tenderness, or worse picture is evident – irrigate the bladder (continuous infusion) with amphotericin. For non-neutropenic patients, fluconazole may be reasonable, and for renal insufficiency of fungi other than Candida one may try caspofungin. Be wary of dissemination, as it is often missed on blood cultures [Intensive Care Med 20: 522, 1994]. Evaluate the fundi, urine, sputum, vascular catheters.