I. Definition
Presence of microorganisms in the urine that have the potential to invade tissues of the urinary tract and adjacent structures, such as the bladder, urethra, prostate, renal parenchyma (kidneys), and collecting system.
Associated with a positive urine culture: more than 100,000 colonies in asymptomatic patients and between 100 and 10,000 colonies in symptomatic patients.
II. Etiology/incidence
A. Urinary tract infections (UTIs) account for 7 million office visits annually.
B. UTIs are more common in women than in men.
C. UTI is the most common bacterial infection in the elderly, and nursing home patients are more likely to have resistant pathogens compared with others of the same age.
D. Escherichia coli is the most common causative organism (70% to 80% of cases), followed by Staphylococcus saprophyticus (5% to 15% of cases).
1. Nosocomial infections may include Proteus spp, Klebsiella spp, Enterobacter spp, Pseudomonas, staphylococci, and Enterococcus faecalis.
2. In patients who are critically ill and those who are chronically catheterized, Candida spp have become a common cause.
3. In the elderly, the following organisms are commonly found: Proteus, Klebsiella, Enterobacter, and Pseudomonas. Other Enterobacteriaceae are also isolated; these include Proteus mirabilis, Klebsiella pneumoniae, Citrobacter spp, Serratia spp, Providencia spp, and Morganella morganii. Coagulase-negative staphylococci, group B streptococci, Enterococcus spp, Pseudomonas aeruginosa, and, occasionally, Candida spp are also found.
E. Risk factors for both genders:
1. Diabetes mellitus
2. Urinary instrumentation and catheterization
3. Obstruction of normal flow of urine due to calculi, tumors, urethral strictures
4. Neurogenic bladder disease resulting from stroke, multiple sclerosis, spinal cord injury
5. Vesicoureteral reflux
F. Contributing factors in women:
1. Short urethra
2. Sexual intercourse
3. Use of a diaphragm and spermicide
4. Pregnancy
G. Contributing factors in men:
1. Prostatic enlargement, resulting in urine residual
2. Prostatitis
3. Homosexuality
4. Having a sexual partner with vaginal colonization by uropathogens
5. HIV infection with CD4+ T-lymphocyte counts lower than 200/mm3
III. Clinical manifestations
A. Lower urinary tract (cystitis/urethritis/prostatitis)
1. Dysuria
2. Frequency
3. Urgency
4. Nocturia
5. Suprapubic pain
6. Hematuria with bacteriuria
7. Malodorous urine
8. Incontinence
9. Fever and chills are uncommon but may be present.
10. No flank or costovertebral pain
B. Upper urinary tract (pyelonephritis, renal abscess)
1. Flank pain
2. Fever
3. Hematuria
4. Nausea and vomiting
5. Mental status changes (in elderly patients)
6. Malaise
7. Shaking chills (rigors)
8. Tachypnea
9. Tachycardia
10. If symptoms last for longer than 3 days, abscess formation should be considered.
IV. Laboratory findings/diagnostics
A. Clean-catch urinalysis with culture and sensitivity testing
B. Pyuria: presence of more than 10 leukocytes/ml
C. Bacteriuria: more than 100,000 bacteria/ml; indicates active infection
1. Bacterial counts of 10,000 to 100,000/ml may also indicate infection, especially if accompanied by pyuria.
2. In urine specimens obtained by suprapubic aspiration or in-and-out (I&O) catheterization, bacterial colony counts of 100 to 10,000/ml indicate infection.
D. Leukocyte esterase dipstick test: positive (purple in 60 seconds)—signifies pyuria or white blood cells (WBCs) in the urine. False-positives may occur with kidney stones, tumors, urethritis, and poor collection techniques. False-negatives may occur with uncomplicated or early UTIs.
E. Nitrate dipstick test: positive for protein, blood, nitrates (pink in 30 seconds)—may be false-negative in uncomplicated UTI, with diuretics early in the course of UTI, with inadequate levels of dietary nitrates, or in the presence of bacteria that do not produce nitrate reductase, such as Staphyloccus saprophyticus, Enterococcus, and Pseudomonas
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