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    OB/GYN Infection: Cystitis


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    By Mark G. Martens, MD

    Here is a review of diagnostic tests and appropriate antimicrobials for this very common condition.

    Cystitis, or lower urinary tract infection (UTI), is a common malady, estimated to occur at least once in 20% of all women in their lifetime. The incidence of bacteriuria varies between 4% and 6% in the reproductive-aged group and increases 1% to 2% per decade, bringing the rate to approximately 10% by the early postmenopausal years.


    Colonization of the vaginal introitus and periurethral region by Enterobacteriaceae or gram-positive organisms from the gastrointestinal tract is thought to be the initial step in the pathogenesis of UTIs in women. Progression to cystitis appears related to several factors, including intercourse, personal hygiene, and diaphragm use.


    The most common cause of uncomplicated cystitis is Escherichia coli (80% to 85% of cases), with other gram-negative bacteria such as Klebsiella, Proteus, Enterobacter, and Pseudomonas species also contributing. The most common gram-positive bacteria recovered in women are Staphylococcus saprophyticus (11%). Staphylococcus epidermidis, the enterococci, and group B ß-hemolytic streptococci are also possible pathogens.


    Asymptomatic bacteriuria is defined as two consecutive urine samples of 100,000 colony-forming units (cfu) per milliliter of urine, collected by the clean-catch method from a patient with no complaints. However, unless the patient is pregnant and undergoes prenatal urine analysis, asymptomatic bacteriuria usually goes undetected. Typically, the condition is detected when a woman is screened for other reasons, has a voiding difficulty, or experiences suprapubic pain. Examination of the urine in an infected patient reveals evidence of pyuria and hematuria approximately 50% of the time.

    In a patient with clinical symptoms, UTI is initially diagnosed by demonstrating large numbers of bacteria and white blood cells (WBC) in the urine. The bacteria should be visible by microscopic examination of an unspun specimen, and more than 50 WBC should be seen per high-power field in a spun specimen. Samples can then be sent for Gram's staining and culture, and treatment initiated.

    Urine containing more than 105 bacteria/mL in a woman with clinical symptoms is diagnostic of cystitis. However, 30% to 50% of women with acute lower-tract infections will harbor fewer than 105 bacteria/mL. Stamm and co-workers, using suprapubic aspiration, found "greater than 102 bacteria/mL" to be the best diagnostic criterion, with a sensitivity of 95%.


    Cost analyses have demonstrated that 90% of cystitis cases are uncomplicated and respond readily to the empiric antimicrobials chosen, without the use of a culture. However, cultures are indicated and helpful in several circumstances. These are listed in Table 1.


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    Gram's stain of the urine sample can help direct initial therapy. Penicillin and ampicillin, though inexpensive and effective, are not considered to be first-line UTI agents because of the increasing resistance of several gram-negative organisms, particularly E coli. Initial therapy can be effectively carried out with one of several relatively inexpensive oral agents, such as nitrofurantoin macrocrystals, 50 to 100 mg every 6 to 12 hours; trimethoprim/sulfamethoxazole, one to two tablets every 12 hours; or sulfamethoxazole or sulfisoxazole, 2 g initially, then 500 mg to 1 g every 6 to 8 hours (Table 2). These agents provide excellent activity against the most common gram-positive and gram-negative uropathogens. However, sulfa regimens have recently been reported to be losing much of their efficacy, so regional trends should be investigated. Another option is fosfomycin tromethamine, now available as a single 3-g oral dose for the specific treatment of women with uncomplicated UTI.


    Click here to view full-size graphic


    Quinolone antibiotics such as ciprofloxacin, ofloxacin, and levofloxacin; the ß-lactamase-inhibiting combination of amoxicillin and clavulanate; and the extended-spectrum agents cefuroxime, cefixime, and cefpodoxime should be reserved for resistant or complicated UTI, because of their higher costs.

    Note, however, that accumulating data suggest quinolone agents may be cost-effective as first-line treatment in certain circumstances. Approximately 20% of women treated for simple cystitis will have a recurrence. In these cases, the newer agents can be given if resistance to first-line agents is documented by culture (Table 2). Three-day treatment regimens appear to be as effective as a 7-day treatment course for initial UTI. Several recent reports demonstrate adequate efficacy with single-dose therapy. However, the morbidity associated with recurrences and retreatment still requires further evaluation of this abbreviated regimen. Individuals who remain symptomatic following treatment when the infecting organism has not been isolated by culture should be evaluated for other conditions, such as trichomoniasis, urethritis, and interstitial cystitis.

    Reinfections usually occur more than 2 to 3 weeks after cessation of previous therapy, and in 95% of cases they usually are due to a different organism. In evaluating these patients, radiographic and endoscopic examinations of the urinary tract are rarely beneficial. The most significant diagnostic aids are culture of the organism and antibiotic sensitivity determinations. Strategies for managing frequent reinfections include prophylaxis, intermittent self-start therapy, and postcoital prophylaxis.

    Relapse or persistence with the same pathogen represents about 5% of cases. These usually occur within 1 to 2 weeks of cessation of antimicrobial therapy and are often associated with structural abnormalities of the urinary tract. Strategies for managing relapse include evaluating the urinary tract radiologically and endoscopically and continuing courses of antimicrobial therapy for 2 to 6 weeks or longer.


    Carey JC, Wilkerson RG. Urinary tract infections in women. In: Pastorek J, ed. Obstetric and Gynecologic Infectious Disease. New York, NY: Raven Press; 1994:85-88.

    Martens MG, Finkelstein LH. Daily cinoxacin as prophylaxis for urinary tract infections in mature women: a prospective trial. Adv Ther. 1995;12:207-211.

    Stamm WE. Dysuria: establishing a diagnostic protocol. Contemporary OB/GYN. 1988;32:81-93.

    Dr. Martens is Professor and Vice Chairman, Department of Obstetrics and Gynecology, University of Minnesota School of Medicine, and Chairman, Department of Obstetrics and Gynecology, Hennepin County Medical Center, Minneapolis, Minn.

    Adapted from Mead PB, Hager WD, Faro S, eds. Protocols for Infectious Disease in Obstetrics and Gynecology. 2nd ed. Malden, Mass: Blackwell Science Inc; 1999.

    Mark Martens. OB/GYN Infection: Cystitis. Contemporary Ob/Gyn 2000;2:15-22.


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