A. Asymptomatic bacteriuria is especially common in women, as evidenced by a minimum prevalence of 2% to 4% in young and 10% in elderly women and a three to four times higher prevalence of asymptomatic bacteriuria in diabetic women compared with their nondiabetic counterparts. The higher incidence of asymptomatic bacteriuria in diabetic women is attributed to lower urinary cytokine and leukocyte concentrations and enhanced adherence to uroepithelial cells of E. coli that express type 1 fimbriae.

The cumulative prevalence of asymptomatic bacteriuria in women increases approximately 1% per decade throughout life. Of note, this phenomenon has been observed in different ethnic groups and geographic locations. In contrast to women, the occurrence of asymptomatic bacteriuria in men is rare until after the age of 60 years, at which time the prevalence increases per decade and often approaches the rate in elderly women. For example, in noncatheterized, institutionalized elderly men, the prevalence of bacteriuria exceeds 20%. Prostatic hypertrophy and increased likelihood of instrumentation are thought to account for the bacteriuria of older men. Moreover, differences between men and women in the rates of bacteriuria have been attributed to the shorter female urethra and its proximity to the vaginal and rectal mucosae and the abundant microbial flora of these areas. Screening for and treatment of asymptomatic bacteriuria is not warranted unless the patient is at high risk for serious complications (e.g., pregnant women and patients undergoing urologic surgery).

Patients in long-term care facilities have an increased risk of asymptomatic bacteriuria as do patients with spinal cord injuries owing to
intermittent catheters, sphincterotomies, or condom catheters. Bacteriuria related to indwelling catheters increases at a rate of 3% to 10% per day and is predominantly asymptomatic. In the absence of UTI symptoms, a positive urine culture for 10⁵ CFU/mL of bacteria is consistent with asymptomatic catheter-associated bacteriuria. Asymptomatic catheterassociated candiduria is defined as 10³ per mL of yeast. The incidence of significant morbidity with asymptomatic bacteriuria and candiduria is low, and antimicrobial therapy is not recommended while the catheter is present.

B. Symptomatic UTIs occur in all age groups. Among newborns and infants, boys are affected more often than girls. When the urinary tract is the source of neonatal sepsis, serious underlying congenital anomalies are frequently present. During childhood, persistent bacteriuria, with or without repeated symptomatic episodes, occurs in a small group (less than 2%) of schoolaged girls. Such girls, and also school-aged boys with bacteriuria, should have a urologic evaluation to detect correctable structural abnormalities when UTIs are documented. Sexually active women have a markedly increased risk of episodes of cystitis. E. coli is the predominant organism in 75% to 90% of cases, whereas Staphylococcus saprophyticus is found in 5% to 15%, primarily in young women. The remainder of cases are due to enterococci and aerobic gram-negative rods, such as Klebsiella species and Proteus mirabilis.

In the absence of prostatitis, bacteriuria and symptomatic UTIs are unusual in men. In fact, asymptomatic prostatitis is very common in men presenting with febrile UTIs. More recently, uropathogenic strains of E. coli have been recognized as causes of cystitis in young men at risk because of homosexuality and anal intercourse, lack of circumcision, or having a partner with vaginal colonization with such P-fimbriated E. coli. At any age, both sexes may develop symptomatic infections in the presence of risk factors that alter urinary flow. Mycoplasma hominis has been well recognized as a sexually transmitted infection and cause of bacterial vaginosis in females and nongonococcal urethritis in males. Ureaplasma urealyticum is a cause of nongonococcal urethritis and chronic prostatitis and can be isolated from expressed prostatic secretions and urine voided after prostatic massage.

A. Acute Urethral Syndrome. The cardinal symptoms of frequency and dysuria occur in more than 90% of ambulatory patients with acute genitourinary tract infections. One-third to one-half of all patients with frequency and dysuria, however, do not have significant bacteriuria, although most have pyuria. These patients have acute urethral syndrome, which can mimic both bladder and renal infections. Vaginitis, urethritis, and prostatitis are common causes of acute urethral syndrome. Although certain signs and symptoms help to differentiate these clinical entities, a classic UTI can be definitively diagnosed only by quantitative cultures of urine.

1. Vaginitis. Approximately 20% of women in the United States have an episode of dysuria each year, and one-half of these seek medical care. The presence of an abnormal vaginal discharge (leukorrhea) and irritation make vaginitis the likely cause of dysuria, unless a concomitant UTI can be confirmed by culture. Candida albicans, the most common specific cause of vaginitis, can be demonstrated readily by culture or by finding yeast cells in a Gram-stained smear of vaginal secretions or in a saline preparation with potassium hydroxide added. Trichomoniasis can be documented with a saline preparation that shows the motile protozoa of Trichomonas vaginalis. Nonspecific vaginitis most often is associated with Gardnerella vaginalis. A clue to this diagnosis is the presence of many small gram-negative bacilli that adhere to vaginal epithelial cells.

2. Urethritis. Acute urinary frequency, dysuria, and pyuria in the absence of vaginal symptoms favor a diagnosis of urethritis or UTI rather than vaginitis. Chlamydia trachomatis is a common cause of the acute urethral syndrome in women, as well as nonspecific urethritis in men. Neisseria gonorrhoeae is also a widespread cause of urethritis and dysuria. The diagnosis and treatment of gonorrhea are now well standardized. Low colony count (100 to 1,000 CFU) infections with coliforms are now a recognized cause of urethritis in symptomatic young women with pyuria. Herpes simplex virus, usually type 2, is another sexually transmitted agent that can cause severe dysuria through ulcerations in close proximity to the urethral orifice. The diagnosis of herpes progenitalis can be confirmed by finding giant multinucleated transformed cells in epidermal scrapings stained with Wright’s stain (Tzanck smear), by isolating the virus in tissue culture, or by direct fluorescent antibody test.

3. Prostatitis. Prostatitis is a common affliction in men that causes dysuria and urinary frequency in middle-aged and younger men more frequently than UTIs do. In addition, more than 90% of men with febrile UTIs have asymptomatic prostatitis manifested by elevated prostate-specific antigens (PSAs) and prostate volume. The PSA may remain elevated for up to 12 months. Prostate syndromes have classically been divided into four clinical entities: (a) acute bacterial prostatitis, (b) chronic bacterial prostatitis, (c) nonbacterial prostatitis, and (d) prostatodynia.

a. Acute bacterial prostatitis is easily distinguished from the other prostatitis syndromes by its acute characteristics. The patient often appears acutely ill, with the sudden onset of chills and fever, urinary frequency and urgency, dysuria, perineal and low back pain, and constitutional symptoms. Rectal examination should not be performed
because of the risk of precipitating sepsis, but it may disclose an exquisitely tender, hot, and swollen prostate gland. Microscopic examination of the urine usually displays numerous white blood cells. Urine culture is usually positive for enteric gram-negative bacteria (especially E. coli); gram-positive bacteria (staphylococci and enterococci) are less frequently isolated.

b. Chronic Bacterial Prostatitis. A hallmark of chronic prostatitis is relapsing UTIs. Urinary frequency, dysuria, nocturia, and low back and perineal pain are the usual symptoms, although patients may have a minimum of symptoms between UTIs. The patient is often afebrile, does not appear acutely ill, and may have an unremarkable prostate examination. A proposed mechanism to explain the migration of bacteria into the prostate is by reflux of urine and bacteria into the prostatic ducts from the urethra. This syndrome is distinguished from other forms of chronic prostatitis by displaying an initial negative midstream urine examination and culture; after prostate massage, however, the urine displays a positive microscopic examination for white blood cells, and a uropathogen can be cultured (see Section V). Nonbacterial prostatitis is the most common form of chronic prostatitis. It mimics chronic bacterial prostatitis clinically and displays inflammatory cells on post-prostate massage specimens. However, bacteriologic cultures of urine and prostatic secretions are sterile. The etiology is unknown, but some evidence exists for an infectious etiology involving organisms that are difficult to culture.

c. Prostatodynia has also been referred to as chronic noninflammatory prostatitis. Clinically, it presents with symptoms similar to other forms of chronic prostatitis. It is distinguished by the absence of inflammatory cells or uropathogens from all specimens.

B. UTIs. Despite the mimicking syndromes, a presumptive diagnosis of infections of the urinary tract can be established economically by analyzing urine in patients with characteristic, albeit nonspecific, signs and symptoms. Acute uncomplicated UTIs occur mainly in women of childbearing age. The presenting features are only suggestive of the site of infection. Patients with bacterial cystourethritis, as distinct from urethritis caused by a sexually transmitted disease (STD) pathogen, will have had prior episodes, will have experienced symptoms for less than 1 week, and will experience suprapubic pain.

1. Indications. The diagnosis of UTI, from simple cystitis to complicated pyelonephritis with sepsis, can be established with absolute certainty only by quantitative cultures of urine. The major indications for urine cultures are as follows:

2. When universally applied, the first two indications may not be the most cost-effective approach to diagnosing UTIs in nonpregnant, young adult women. These individuals present with dysuria, urgency, and pyuria due to an uncomplicated episode of cystourethritis, with organisms usually susceptible to a variety of antimicrobial agents, or due to an STD pathogen such as gonococcus or chlamydia. Moreover, because the beneficial outcome of therapy is to minimize morbidity rather than prevent life-threatening complications, laboratory costs and use of resources can be minimized if pretreatment cultures are not ordered in this clinical setting. Therefore, women with symptoms consistent with simple uncomplicated lower tract disease and a positive urine dipstick can be treated without obtaining a urine culture. Additionally, if symptoms completely resolve, posttreatment cultures are also unnecessary for patients with uncomplicated infections.

3. Methods. Urine specimens must be cultured promptly within 2 hours or be preserved by refrigeration or a suitable chemical additive (e.g., boric acid sodium formate preservative). Acceptable methods of collection are the following:

4. Not acceptable, because of constant contamination and the impossibility of quantitative counts, are tips from indwelling urinary catheters and urine obtained randomly, without adequate patient preparation. The clean-voided, midstream technique of collection is preferred whenever possible to avoid the risk of introducing infection at the time of catheterization, a hazard in elderly patients confined to bed, in men with condom catheters, and in diabetic patients with dysfunctional bladders. Because contamination is exceedingly rare in circumcised men, a cleancatch, midstream specimen is unnecessary in such patients. Occasionally, suprapubic aspiration of the bladder is necessary to verify infection. This technique has been most helpful in obtaining specimens from possibly septic infants and from adults in whom repeated clean-voided specimens have yielded equivocal colony counts on culture.

5. The usual microbial pathogens isolated from patients with UTIs are listed in Table 7-1. Results of cultures highly depend, however, on the clinical setting in which bacteriuria occurs. For example, E. coli is found in the urine of 80% to 90% of patients with acute uncomplicated cystitis and acute uncomplicated pyelonephritis. S. saprophyticus is another common cause of UTI, but rarely causes acute pyelonephritis. Many patients with staghorn calculi of the kidneys harbor urea-splitting Proteus organisms in their urine. Klebsiella, Pseudomonas aeruginosa, and Enterobacter infections are commonly acquired in the hospital. The presence of Staphylococcus aureus in the urine most often is a clue to concomitant staphylococcal bacteremia, unless an underlying risk factor exists. Microorganisms in young men are similar to the organisms that cause uncomplicated infections in women. Enterococci and coagulase-negative staphylococci are more common in elderly men, most likely representing recent instrumentation or catheterization. C. albicans is rarely encountered, except in patients with indwelling catheters, nosocomial UTIs, or relapsing infections after multiple courses of antibiotic therapy. Most urinary catheter-related infections originate from the patient’s colonic flora with long-term catheterization exceeding 28 days. Multidrug-resistant organisms such as Providencia stuartii, Pseudomonas spp., Proteus spp., Morganella spp., and Acinetobacter spp. are found more frequently owing to antibiotic exposure. In addition, polymicrobial bacteriuria is found in up to 95% of urine cultures from patients with long-term catheter use. Although the likely microorganism and usual susceptibility patterns are sufficient to guide the initial empiric therapy of uncomplicated cystitis, adequate treatment of acute bacterial pyelonephritis and complicated UTIs necessitates precise therapy based on isolation of the causative bacterium and standardized antimicrobial susceptibility testing using the disk-diffusion or the broth-dilution or agar-dilution methods.

B. Interpretation of Urine Cultures. Organisms residing in the distal urethra and on pubic hairs contaminate voided, clean-catch specimens. This bacterial contamination must be distinguished from “true infection” or “significant bacteriuria” in urine cultures. Quantitative bacteriology makes this distinction. Because quantitation of bacteriuria is so important clinically, methods for culture of urine must enable the CFU number of a potential pathogen per milliliter of urine to be assessed. The standard procedure involves the use of calibrated bacteriologic loops that deliver a known volume of urine to the surface of agar plates. Proper plating techniques achieve isolated colonies that can be enumerated accurately. A satisfactory alternative for the diagnosis of uncomplicated UTIs is the dip slide method, which is particularly well suited to quantitative urine cultures in smaller clinics. Rapid methods based on filtration and colorimetry, bioluminescence, growth kinetics, and biochemical reactions are used increasingly to screen urine specimens for the presence of bacteria. The sensitivities of these rapid assays are in the range of 10⁴ to 10⁵ CFU/mL. The simplest screen is the paper-strip test for detection of leukocyte esterase and nitrite in first morning urine specimens. However, these methods are not a substitute for standard cultures in symptomatic patients with complicated UTIs.

1. Colony Counts. Figure 7-2 shows a basic guide to the interpretation of quantitative cultures of urine. Colony counts greater than 10⁵ CFU/mL in properly collected and transported specimens usually indicate infection. Colony counts of 10³ or fewer CFU/mL from untreated patients are uncommon with true UTIs, except in symptomatic young women with pyuria and urethritis, in whom colony counts of E. coli as low as 10³ may be interpretable if the urine was obtained by single catheterization. Intermediate counts, especially with mixed flora, usually imply poor collection or delayed transport and culture. Brisk diuresis may transiently reduce an otherwise high colony count.

2. Suprapubic Needle Aspiration. Any growth from urine obtained by suprapubic needle aspiration may be important. Use of a 0.01 mL
quantitative loop for culturing aspirated urine permits the detection of as few as 100 CFU/mL. Two or more colonies (≤200 CFU/mL) of the same microorganism ensure the purity of growth from such specimens and permit standardized antimicrobial susceptibility testing. Similar criteria should be used for patients who are receiving antimicrobials at the time of culture. Except in unusual circumstances, the isolation of diphtheroids, α-hemolytic streptococci, and lactobacilli indicates contamination of the urine specimen with vaginal or periurethral flora.

3. Prostatic Secretions.

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