Introduction
Urinary tract infection (UTI) is a common problem in the elderly. Diagnosis, prevention, and treatment can often be complex because clinical manifestations can be atypical and host defenses diminish with age. Common risk factors are listed in Table 100-1.
Classification
Bacterial UTIs can be classified according to localization as urethritis (urethra), cystitis (bladder), or pyelonephritis (kidney). In men, prostatitis may mimic or complicate UTI. Alternatively, UTI can be classified by the presence (symptomatic) or absence (asymptomatic) of symptoms, the frequency of its occurrence, the presence or absence of complications, and--especially important in the elderly--whether UTI is associated with catheter use.
Asymptomatic bacteriuria is characterized by >= 105 colony-forming units (CFU)/mL without dysuria, urinary frequency, incontinence of recent onset, flank pain, fever, or other signs of infection during the week preceding the time the urine sample was obtained. Small numbers of polymorphonuclear leukocytes (PMNs) are common. Only about 70% of asymptomatic patients with high colony counts in a single urine sample have true bacteriuria as confirmed by the second sample.
Sporadic infections are defined as >= 3 (or >= 2, according to some investigators) episodes of asymptomatic bacteriuria within 1 year. Recurrent infections are classified as either relapse or reinfection UTI. Relapse UTI is defined as an infection in which urine is rendered partially or temporarily sterile by antimicrobial therapy, with the subsequent recurrence of bacteriuria from the uneradicated pathogen, generally within 2 weeks of completion of therapy. Reinfection UTI is defined as an infection that arises >= 4 weeks after the previous infection has been cured; the bacterial strain is often different from the strain that caused the successfully treated prior infection.
Complicating factors include urinary calculi, abscess formation, and obstructive uropathy. All UTIs in men are considered complicated whether or not these factors exist.
Epidemiology and Etiology
The prevalence of UTI increases in both sexes with age; the female:male ratio is 2:1 in the elderly. The annual incidence of symptomatic bacterial UTIs is estimated to be as high as 10% in the elderly. However, because many of these infections are recurrent, the percentage of infected patients is lower. Asymptomatic bacteriuria is a common finding in the elderly, especially in women; the estimated cumulative prevalence is 30% in women and 10% in men.
More types of urinary pathogens are isolated from elderly patients with UTI than from younger patients. The severity of any functional disability, nature of underlying illnesses, presence of anatomic or physiologic abnormalities of the genitourinary (GU) tract, and use of indwelling bladder catheters determine the types of organisms and chronicity of bacteriuria. Escherichia coli accounts for <= 70% of bacteriuria in elderly female outpatients with uncomplicated sporadic cystitis and for about 40% in patients with indwelling bladder catheters, complicated infections, or nosocomial infections. Other Enterobacteriaceae, enterococci, and staphylococci are often found.
Klebsiella sp, especially K. pneumoniae, are the second most commonly isolated gram-negative, aerobic pathogens. Proteus mirabilis, P. vulgaris, P. inconstans, and Morganella morganii are more common in men than in women because these species tend to dominate the normal aerobic preputial flora. They are also commonly isolated from the urine of patients with calculi, because they grow best in an alkaline milieu, and from patients with urogenital tumors. Proteus sp, M. morganii, and Providencia sp are commonly isolated from patients who are chronically catheterized. Serratia, Enterobacter, Citrobacter, Acinetobacter, and Pseudomonas sp are isolated mainly from patients with nosocomial UTIs.
In patients with recurrent infections, resistant gram-negative bacteria other than E. coli and gram-positive bacteria tend to predominate. Of the latter, enterococci, coagulase-negative staphylococci, and group B streptococci are commonly isolated; enterococcal superinfection often results from frequent use of antibiotics that are inactive against these organisms (eg, quinolones, cephalosporins, sulfonamides).
Anaerobes may be rarely isolated from patients with rectovesical fistulas or other abnormal communications between the urinary tract and bowel, which allow anaerobic fecal flora direct access to the urine.
Pathogenesis
In the elderly, the female/male ratio of incidence in UTIs narrows, in part because elderly men often have bladder outlet obstruction due to benign prostatic hyperplasia. Additionally, the relative reduction in the incidence of UTI in elderly women may be due to a decrease in sexual activity, which can introduce bacteria into the bladder. Severe UTIs, particularly those complicated by septicemia originating from the urinary tract, become more common with age, in part because of more frequent bladder catheterization and instrumentation and possibly because of changes in the immune system. Recurrent and complicated infections are also more common because of the higher frequency of predisposing anatomic and pathophysiologic factors, such as prolapse, urolithiasis, and malignancies in the GU tract and uterus.
Bacteria proliferate in stagnant bladder urine, and clinically important bacteriuria becomes established. A large amount of postvoiding residual urine is most common with a neurologic disorder, bladder outlet obstruction, or urethral stricture. A residual urine of 5 to 20 mL is fairly common in otherwise healthy elderly persons. Foreign bodies, most commonly indwelling bladder catheters, also promote bacterial growth. In catheterized patients, clinically important bacteriuria is established within 14 days unless a closed and aseptically handled system is used. However, recent data suggest that the majority of cases of asymptomatic bacteriuria in the elderly are true infections rather than colonizations. In addition to pyuria, elevated urine and serum antibodies to the implicated uropathogen and measurable urinary interleukin (IL)-6, IL-1a, or IL-8 have been shown to be present in nearly 90% of elderly patients with asymptomatic bacteriuria. The clinical relevance of these observations is unclear.
Symptoms, Signs, and Diagnosis
Many patients are asymptomatic. Symptoms that may occur include dysuria, urinary frequency, incontinence of recent onset, flank pain, and fever. Confusion and delirium are often attributed to UTI, although without high fever or sepsis, uncomplicated UTI is unlikely to cause serious central nervous system dysfunction.
The diversity of potential uropathogens mandates that urine cultures be obtained in all elderly persons with suspected UTI.
Bacteriologic diagnosis of complicated, recurrent UTIs and of asymptomatic bacteriuria is usually based on the concept of clinically important bacteriuria, which for these patients is usually defined as > 105 CFU/mL in a midstream urine sample after > 4 hours of bladder incubation. For women with uncomplicated symptomatic cystitis, however, the highest diagnostic sensitivity and specificity are achieved when clinically important bacteriuria is defined as > 102 CFU/mL with pyuria. If the clinical importance of bacteriuria is doubtful (eg, when repeated samples yield more than one bacterial strain) and obtaining culture is critically important, urine may be obtained by bladder puncture (which is better than bladder catheterization because the risk of contamination is minimized). However, bladder puncture may be more difficult to perform in elderly patients, and straight bladder-catheterized specimens often have to suffice.
Rapid tests can provide a semiquantitative determination of bacteriuria. The best is the nitrite test, in which the conversion of nitrate to nitrite by bacteria in the urine is demonstrated by color change on a dipstick. This test has a high degree of sensitivity and specificity but does not demonstrate bacteriuria caused by Pseudomonas sp, staphylococci, or enterococci, which are incapable of reducing nitrate to nitrite.
Quantitative urine cultures can be performed in bacteriology laboratories. The urine must be refrigerated if culture and incubation are delayed; however, storage for > 4 to 8 hours should be avoided, because substantial bacterial replication still occurs, even at cold temperatures. Quantitative urine cultures also identify the species involved and determine antibiotic susceptibility. In outpatient clinics, a dip-slide culture (in which an agar-covered slide is dipped in urine and incubated or left at room temperature overnight) may be used. The number of bacteria in the sample is reliably quantified, and gram-negative and gram-positive organisms are differentiated. A positive dip-slide can later be sent to a bacteriology laboratory for identification of species and determination of antibiotic susceptibility. Pyuria (presence of > 10 PMNs/high-power field under light microscopy in the urine) suggests infection rather than colonization.
Recurrent UTIs: In addition to bacteriologic diagnosis, more testing is often necessary, including quantitation of postvoiding residual bladder urine volume and investigation of the architecture of the upper urinary tract via ultrasound or CT in select cases. Urologic consultation may be sought when obstructive uropathy, calculi, abscesses, or GU tract anatomic abnormalities are suspected. Chronic bacterial prostatitis can also result in relapse UTI in elderly men. The diagnosis is suggested when bacterial colony counts from urine or expressed prostate secretion are at least 10-fold greater than counts from the urethral urine sample. Also, the presence of neutrophils in the prostatic secretions substantiates the diagnosis. In relapse UTI, evaluation should include assessment of bladder anatomy and function (ie, postvoiding residual and voiding cystogram or cystoscopy).
Treatment
Asymptomatic bacteriuria: In women, asymptomatic bacteriuria should not be treated unless coexisting conditions increase the risk of symptomatic invasive disease. In untreated asymptomatic bacteriuria, the organisms (especially E. coli) lose their virulence and become extremely susceptible to the bactericidal effect of normal human plasma. Large amounts of bacteria in the urine may therefore protect against symptomatic bacteriuria caused by more virulent strains.
In men, asymptomatic bacteriuria should be investigated to exclude complicating factors such as residual urine, calculi, or tumors. While the diagnosis is being determined and causative factors are eliminated, treatment should usually be given.
Cystitis: Most elderly women with uncomplicated lower tract UTI should be treated with antibiotics for 10 days; elderly men are generally treated for 14 days. Abbreviated courses (< 7 days) of treatment for UTI are not recommended for elderly patients because of relatively high rates of failure and relapse. Patients with community-acquired infections can be treated with trimethoprim-sulfamethoxazole (TMP-SMX) or an oral cephalosporin (eg, cephalexin, cefuroxime). When organisms are resistant or when the risk of pyelonephritis is high, a fluoroquinolone (eg, norfloxacin, levofloxacin, ciprofloxacin) can be used. Ampicillin and amoxicillin are generally not preferred because at least 13% of E. coli strains are resistant to them. For elderly patients with recurrent, complicated, or nosocomial infections, a fluoroquinolone or TMP-SMX, with ampicillin, is recommended before the cephalosporins; ampicillin adds coverage against sensitive enterococcal isolates.
For patients who have recurrent cystitis or for whom instrumentation of the lower urinary tract is planned, prophylactic treatment may be considered using nitrofurantoin one 50- to 100-mg dose at night (lower doses should be given to patients with markedly reduced renal function) or TMP-SMX 80 to 400 mg (half or full tablet nightly or one tablet 3 times/week). Prophylactic therapy should be avoided in patients with indwelling bladder catheters.
Pyelonephritis: Men and women with infection of the upper urinary tract (eg, presence of urosepsis, flank tenderness, fever > 38.3° C [> 101° F]) should be treated for a minimum of 14 days. Antibiotics for initial oral treatment include fluoroquinolones (eg, norfloxacin, ciprofloxacin, levofloxacin), oral cephalosporins (eg, cefuroxime), and TMP-SMX. For patients with community-acquired infections who have not received previous antibiotic treatment, a 2nd-generation cephalosporin (eg, cefuroxime) covers most pathogens; for patients with nosocomial infections, a 3rd-generation cephalosporin (eg, cefotaxime, ceftazidime, ceftriaxone), aztreonam, or an aminoglycoside is preferred. An alternative is treatment with IV TMP-SMX or a quinolone.
Urosepsis: Urosepsis in elderly persons may give rise to high morbidity and mortality rates. First-line antibiotics for urosepsis include 2nd- and 3rd-generation cephalosporins, quinolones, aztreonam, and aminoglycosides with ampicillin for about 2 weeks. Although the highest recommended initial dose should be used, subsequent doses usually need to be reduced substantially because of decreased renal function in the elderly. Maintenance of fluid and electrolyte balance as well as of adequate blood pressure is critical.
Relapse UTI: Treatment depends on the underlying etiology. Chronic bacterial prostatitis should be treated for a minimum of 4 weeks with drugs such as oral quinolones or TMP-SMX.
Reinfection UTI: Management of uncomplicated reinfection UTI includes hydration and acidification of urine and low-dose suppressive antibiotic therapy.
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