Chapter Outline
Urinary tract infections account for eight million health care visits per year at the cost of $1.6 billion. Fifteen percent of all outpatient prescriptions written are for urinary tract infections. Clinicians managing patients with urogynecologic problems need to be well versed in the diagnosis and management of urinary tract infections, because the rates of urinary tract infection are particularly high among menopausal women, pregnant women, women in nursing homes, patients with incontinence or voiding dysfunction, and patients undergoing procedures that require instrumentation of the genitourinary tract.
Epidemiology and Risk Factors
At least 50% of women experience a urinary tract infection during their lifetime, with approximately 5% experiencing frequent infections. Acute uncomplicated pyelonephritis is significantly less common than lower urinary tract infections, and occurs approximately once for every 28 episodes of acute cystitis. Urinary tract infections are more prevalent among women than among men (ratio of 20:1), likely owing to the relatively short female urethra, which puts the urinary tract in close proximity to the flora of the vagina and rectum.
The prevalence of urinary tract infections increases with age ( Fig. 39.1 ). The rate of bacteriuria is 1% to 2% in young children, then doubles among young women ages 15 to 24, gradually increases to approximately 15% at age 60, and continues to climb to rates of 25% to 50% after age 80. Whereas sexual activity and pregnancy are significant risk factors among younger women, vaginal atrophy, pelvic floor relaxation, systemic illness, and hospitalization are more important risk factors in older women.
Urinary tract infections account for 500,000 nosocomial infections per year, 1% of which become life-threatening. Instrumentation or catheterization of the urinary tract is a precipitating factor in at least 80% of these infections. Catheterization is associated with a risk of urinary tract infection of 3% to 6% per day with an indwelling catheter and 1% to 3% per day with clean intermittent catheterization.
Women undergoing gynecologic surgery are at particularly high risk of urinary tract infection. The risk seems to be highest among women who undergo surgery for pelvic organ prolapse and incontinence, who require postoperative catheterization. In one trial, 33% of patients developed a symptomatic lower urinary tract infection within 8 weeks of surgery. Other known risk factors for urinary tract infection are listed in Box 39.1 .
| Advanced age |
| Genetic predisposition |
| Mother with history of recurrent urinary tract infection |
| Nonsecretors of ABH blood type antigens |
| P blood group |
| Physiologic changes |
| Pregnancy |
| Shift of vaginal flora after antibiotic use |
| Increased vaginal pH in menopausal women |
| Inefficient emptying |
| Pelvic organ prolapse: cystocele or uterovaginal prolapse with obstructive voiding pattern |
| Neurogenic bladder (e.g., diabetes, multiple sclerosis, spinal cord injury) |
| Anticholinergic medications |
| Instrumentation (catheterization, cystoscopy) |
| Decreased functional ability |
| Dementia |
| Cerebrovascular accident |
| Neurologic disease |
| Fecal incontinence |
| Sexual intercourse, diaphragm use, spermicide use |
Microbiology
Gram-negative bacilli are responsible for 90% of urinary tract infections. Escherichia coli is the single most important organism and accounts for 80% to 90% of uncomplicated infections. Staphylococcus saprophyticus is the second most common cause of cystitis and causes approximately 10% of infections in sexually active females. Other common pathogens in urinary tract infections include Klebsiella , Enterobacter , Serratia , Proteus , Pseudomonas , Providencia , and Morganella species. Pseudomonas aeruginosa infection almost always results from urinary tract instrumentation. Staphylococcus epidermidis is a nosocomial pathogen identified in patients with indwelling catheters. Staphylococcus aureus is less commonly isolated and is often caused by hematogenous renal infection. Other gram-positive organisms such as enterococci and Streptococcus agalactiae cause about 3% of episodes of cystitis. Enterococcus faecalis causes about 15% of nosocomial urinary infections, and S. agalactiae is more commonly the cause in patients with diabetes mellitus. Anaerobic bacteria, although abundant in fecal flora, rarely cause urinary tract infections.
Candida albicans and other fungal organisms can cause lower urinary tract infections in patients with diabetes mellitus, with indwelling urinary catheters, or an immunocompromised state. Viruria has been documented with many viruses, but generally in association with viremia. Viral urinary tract infections occur as acute illnesses (acute hemorrhagic cystitis in children, and polyoma virus infection after bone marrow transplant), during convalescence from viral infections (mumps and cytomegalovirus), and in asymptomatic patients (cytomegalovirus).
Pathogenesis
Most urinary tract infections are ascending infections in which the fecal flora initially colonize the vaginal introitus and periurethral tissues, eventually gaining entry into the bladder. Virulence factors including fimbria and other adhesins facilitate ascent up the urinary tract, mucosal adherence, and stimulation of the host immune response.
Factors that typically help deter the development of a urinary tract infection include acidic vaginal secretions, acidic urine, periodic voiding, the glycosaminoglycan (GAG) layer of the bladder, and immunoglobulins in the urine. The acidic pH of the vagina in premenopausal women inhibits the growth of enterobacteria such as E. coli and promotes the growth of lactobacilli and other gram-positive bacteria that typically replicate poorly in urine. The GAGs in the bladder lining and immunoglobulins in the urine block bacterial adherence. Tamm–Horsfall proteins secreted by the loop of Henle may also inhibit bacterial adherence to the urothelial cells. A genetic predisposition to urinary tract infection is likely linked to differences in mucosal bacterial binding properties and can be related to blood type.
Diagnosis
Clinical Presentation
Cystitis in women usually causes dysuria, although it may also cause frequency, urgency, nocturia, and suprapubic discomfort. Occasionally, mild incontinence and hematuria may occur. Gross hematuria is rare. Upper tract infections commonly present with fever, chills, malaise, flank pain, costovertebral angle tenderness, and occasionally nausea and vomiting. These patients may not have signs of acute cystitis.
Differential Diagnosis
The differential diagnosis of a urinary tract infection includes candidiasis, Trichomonas vaginitis, and other sexually transmitted diseases. Vaginal atrophy can also cause urinary tract symptoms that mimic a urinary tract infection. Bladder pain syndrome (interstitial cystitis) and urethral syndrome should also be considered, because they are pain disorders of the urinary tract characterized by lower urinary tract symptoms despite negative urine, vaginal, and urethral cultures. Finally, if the woman has had previous surgeries for urinary incontinence or pelvic organ prolapse, the possibility of suture material, mesh, or stones in the bladder or urethra should be considered.
Diagnostic Criteria for Urinary Tract Infection
The Center for Disease Control (CDC) diagnostic criteria for a urinary tract infection include a urine culture with ≥100,000 colony-forming units (CFU) per mL of no more than two species of microorganisms and one sign or symptom of cystitis with no other recognized cause. Signs and symptoms include urgency, frequency, dysuria, suprapubic tenderness and fever >38.0°C. Alternative diagnostic criteria issued, costovertebral angle pain or tenderness, by the CDC include at least two signs or symptoms with no other identifiable cause and a urine dipstick with leukocyte esterase and/or nitrites, pyuria (≥10 leukocytes/mL or ≥3 leukocytes per high-powered field (HPF) of unspun urine), or organisms on a gram stain of spun urine. Some experts advocate relaxing these diagnostic criteria to include symptomatic patients with pyuria and a urine culture with ≥100 CFU per mL, because approximately 80% of these patients have a urinary tract infection. Lower colony counts on culture may represent a partially treated infection, an earlier stage of infection, or the effects of diluting the bacterial concentration with urination.
Urine Collection Methods
Urine collected for analysis can be a clean catch specimen or a catheterized specimen. However, up to one-third of clean catch specimens are contaminated. To minimize contamination of clean catch specimens, women should be instructed to spread the labia, wipe the periurethral area from front to back with a clean, moistened gauze sponge, and collect a midstream urine sample holding the labia apart. In women unable to obtain a clean voided specimen, such as women who are obese or who are functionally impaired, urethral catheterization or suprapubic aspiration can be performed. The bacterial count is likely to be highest if the urine has been in the bladder for over 4 h, such as with the first void of the day.
Diagnostic Testing
Diagnostic testing for a urinary tract infection includes an office urine dipstick, microscopic urinalysis, and urine culture. Whereas a positive urine dipstick and/or microscopic urinalysis in a symptomatic patient are generally considered sufficient evidence to support empiric treatment of a presumed urinary tract infection, urine cultures should be sent in patients in whom the diagnosis of cystitis is questionable or in whom complicating factors are present. Regardless of the urine testing method used, the urine specimen should be sent to the lab immediately, because bacteria will continue to proliferate if the specimen is kept at room temperature. However, storing the specimen at 4 °C should stop bacterial growth and permit culturing the following day without altering the culture results.
Urine Dipstick
The urine dipstick is a simple urinary tract infection screening tool for office or home use that detects urine nitrites and leukocyte esterase. Gram-negative bacteria convert nitrates to nitrites. Leukocyte esterase corresponds to pyuria and indicates a host immune or inflammatory response. A cost-effectiveness analysis published by indicated that treatment based on urine dipstick results is the most cost-effective management strategy for acute uncomplicated cystitis. However, providers must bear in mind that testing with a dipstick is not always accurate. False positives can occur when the urine is contaminated. False negatives can occur in early infection and with gram-positive infections that do not produce nitrites. Urine dipstick nitrite and leukocyte esterase tests have a sensitivity of 75% and specificity of 82% in patients with ≥100,000 CFU/mL. Thus, in patients with a urinary tract infection, 25% will not have a positive dipstick. In contrast, among women without a urinary tract infection, 18% will have a positive dipstick. Therefore, although dipsticks can provide valuable clinical information, ultimately the provider should use clinical judgment and/or additional diagnostic testing to make a final decision regarding treatment.
Microscopic Urinalysis
Microscopic examination of urine can detect the presence of significant bacteria, leukocytes, and red blood cells. Pyuria is defined as ≥10 leukocytes/mL or ≥3 leukocytes per HPF of unspun urine. In the absence of pyuria, the diagnosis of urinary tract infection should be questioned. However, some examples of sterile pyuria are tuberculosis, renal or bladder calculi, mesh or sutures in the bladder, glomerulonephritis, interstitial cystitis, and chlamydial or Ureaplasma urethritis. Patients may also have sterile pyuria if they have a urinalysis after initiating antimicrobial therapy. Neither microscopic hematuria nor bacteriuria is a particularly sensitive finding and is often negative in the setting of urinary tract infection. For example, approximately 50% of urinary tract infections do not demonstrate hematuria on microscopic exam and bacteria are often unidentifiable in lower colony-count infections.
Urine Culture
Urine culture is considered the reference standard for diagnosis of a urinary tract infection. Cultures should be submitted if there is a suspected complicated urinary tract infection, a negative dipstick in a symptomatic patient, poor response to initial therapy, and recurrent symptoms <1 month after treatment for a previous urinary tract infection for which no culture was performed. Complicated infections occur in the setting of an immunocompromised host, a genitourinary structural or functional abnormality (e.g., urolithiasis, renal insufficiency), pregnancy, and recent antibiotics or genitourinary tract instrumentation. Although a culture result of ≥100,000 CFU/mL has historically been considered a required diagnostic criterion for a urinary tract infection, some feel that ≥100 CFU/mL should suffice in a patient who has symptoms consistent with urinary tract infection and pyuria.
Symptom-Based Diagnosis
Diagnosis of uncomplicated urinary tract infection based on symptoms alone is advocated by some because of the false-negative results encountered with urine dipsticks, as well as the expense and time delay associated with microscopic urinalyses and culture. However, the primary disadvantage of symptom-based diagnosis is that it results in overtreatment and inappropriate antibiotic use. It may also delay the diagnosis of other causes of urinary tract symptoms. performed a double-blind, randomized, placebo-controlled trial of women with urinary tract infection symptoms and negative urine dipstick results. Five of 59 subjects had positive urine cultures of ≥100,000 CFU/mL. Empiric treatment resulted in a median time to symptom resolution of 3 versus 5 days in patients receiving trimethoprim and placebo, respectively ( P = 0.002). At day 7, symptom resolution was higher among trimethoprim patients (90% versus 59%; P = 0.02). The authors concluded that a negative dipstick does not predict response to treatment. Therefore, they endorsed empiric antimicrobial therapy despite the potential adverse effects of widespread antibiotic use.
Additional Studies
Radiographic imaging studies should be considered in patients with poor response to appropriate antimicrobial therapy, infections caused by usual organisms such as Proteus , a history of calculi, potential ureteral obstruction, recurrent pyelonephritis, suspected urethral diverticula, and a history of many urinary tract infections during childhood. A renal ultrasound may be appropriate in any of these patients, although it is optimal for evaluating for a renal abscess or hydronephrosis. A non-contrast computed tomography image (CT) is the current reference standard for radiographic diagnosis of calculi. It is more likely than ultrasound and an X-ray of the kidneys, ureter, and bladder (KUB) to identify small stones and is more likely than a KUB to detect radiolucent stones. Transvaginal ultrasound is often adequate for the detection of urethral diverticula, although magnetic resonance imaging (MRI) can provide more imaging detail, particularly for solid components such as a mass or stone. MRI has been found to have a sensitivity of 86% to 100% for urethral diverticulum.
The indications for cystourethroscopy in women with urinary tract infection are controversial, because findings often do not alter management. However, it is reasonable to consider cystoscopy in patients with inadequate response to appropriate antimicrobial therapy, gross hematuria, suspected urethral diverticulum, and suspected mesh or nonabsorbable suture material in the bladder or urethra. It should also be considered in older patients for whom bladder cancer may be of concern. Urodynamics may be useful in patients with recurrent infections and signs or symptoms of voiding dysfunction.
A suggested approach to the evaluation and treatment of women with acute dysuria is shown in Fig. 39.2 .
