Urinary tract infections UTI

Urinary tract infections (UTIs) remain a significant source of morbidity and mortality. In this country alone, UTIs are responsible for seven million visits to physicians' offices and one million admissions to hospitals. Fortunately, most infections are easy to diagnose and readily treated. Part I of this checklist outlines the current understanding of UTIs and provides basic management principles. Next month, Part II will focus on specific circumstances that may complicate the evaluation and treatment of UTIs.

• How are Urinary tract infections categorized?

The majority of UTIs can be classified as uncomplicated because they occur within a urinary tract that is anatomically and functionally normal and are caused by a limited spectrum of readily treatable bacteria. Simple UTIs include cystitis and even acute pyelonephritis in women. Escherichia coli accounts for more than two thirds of community-acquired infections and 50 percent of nosocomial infections. Not infrequently, Klebsiella spp., proteus, Enterococcus faecalis, and Staphylococcus saprophyticus are the causative pathogens.

Although most UTIs initially can be considered simple, certain features may indicate a potentially more serious problem. In men, the majority of UTIs should be considered complicated. Infections that occur in the setting of an abnormal urinary system or are caused by multidrug-resistant bacteria will need more rigorous treatment and a thorough investigation. Complicated UTIs may require referral to a urologist.

In order to have a better understanding of the etiology of any given infection and plan more efficiently for its evaluation and treatment, urologists have defined four general categories of UTIs. Isolated infections refer to the initial infection and those that occur more than six months apart; approximately 25-35 percent of women between the ages of 20 and 40 experience isolated infections. Reinfections represent new infections and account for most recurrent UTIs. Unresolved infections signify an inability to sterilize the urine, despite treatment, and are often the result of bacterial resistance. Persistent infections are manifest by a recurrence of the same organism, despite initial sterilization of the urine, and indicate that the source of the bacteria resides within the urinary tract.

• What are the symptoms of Urinary tract infections?

All physicians are familiar with the urinary frequency and urgency, suprapubic or lower abdominal pain, dysuria, and occasional hematuria typically associated with a urinary infection. In women, fever and flank pain suggest pyelonephritis. Men with acute prostatitis also may note malaise, chills, lower back pain, groin pain, or testicular pain, along with fever.

The history and physical exam should help determine the necessary subsequent laboratory evaluation. For isolated and very infrequently occurring infections, a simple urinalysis to confirm the presence of pyuria and possibly bacteriuria, followed by a short course of treatment (usually three days), is acceptable. Initially, a simple dipstick can confirm the clinical impression of a UTI by detecting hematuria, pyuria, and a positive leukocyte esterase or nitrite test. More than 95 percent of patients with positive urines will be identified by dipstick testing alone.

• What role does culture and sensitivity testing play?

Failure to respond to initial therapy or a relapse within a short period of time requires urinalysis, along with culture and sensitivity testing. With some experience, microscopic assessment of a urine sample can provide predictive information. An unstained, centrifuged specimen is not only relatively easy to obtain but can predict the presence of an infection with 90 percent accuracy. The identification of one or more organisms per high-power field indicates >105 colony-forming units (CFUs)/mL. Although the definitive diagnosis of a UTI traditionally has required a quantitative urine culture showing bacteria numbering at least 105 CFUs/mL, more recently, as few as 100 coliforms/mL in a midstream, clean-catch urine from women with symptoms are accepted as a positive culture.

There are two simple methods of culturing the urine. The first utilizes split agar disposable plates. One half of the plate is blood agar, which grows gram-positive and gram-negative bacteria, and the other half is deoxycholate or eosin-methylene blue, which grows gram-negative bacteria in a very characteristic way. A small quantity of urine is spread on each portion of the plate, and the plate is kept overnight in a standard incubator. The number of colonies is counted and multiplied by 10 to give the number of bacteria in one milliliter of urine. With some experience, the bacteria can be identified as well.

The other technique employs dipslides, which are plastic slides with agar on one side and eosin-methylene blue or MacConkey agar on the other side for gram-negative bacteria; these are attached to screw-top caps. The slide is dipped in the urine, drained, placed into the accompanying plastic bottle, and incubated. The colony count in the urine is approximately 100 times the number of visible colonies on the slide. Select patients can perform this test at home.

The results of the culture and sensitivity testing will dictate the next step. A simple reinfection requires only another course of antibiotics. Unresolved infections most commonly result from plasmid-mediated resistance; retreatment with an antimicrobial that is effective against the specific organism should prove successful. Reappearance of the same organism indicates a need for further diagnostic studies to identify the underlying abnormality. When pyuria or a vaginal or urethral discharge occurs in a sexually active patient despite negative cultures, additional testing should be undertaken for Chlamydia trachomatis, Trichomonas vaginalis, or Neisseria gonorrhoeae.

• How are Urinary tract infections best managed?

An organized systematic approach will make the management of UTIs simple and economical. Once a presumptive diagnosis is made based on the history and symptomatology, the infection should be categorized as outlined earlier. This will determine the appropriate diagnostic studies and guide the initial selection of an antimicrobial agent.

The treatment of a woman with an uncomplicated UTI is straightforward. If she has not been prescribed an antimicrobial agent for some time, the offending organism most commonly is E. coli, which will be susceptible to most agents. Therefore, a culture is not necessary, and one of the inexpensive antimicrobials should be selected. Some women will be able to recognize the onset of a UTI and can be provided with medication to keep at home, so they can initiate therapy quickly. This is called "self-start therapy."

• What medications are effective for treating Urinary tract infections?

A three-day regimen with trimethoprim/sulfamethoxazole (TMP/SMX) has been shown to be more cost-effective than nitrofurantoin, amoxicillin, or cephalexin and to yield higher cure rates than single-dose therapy (one pill of any antimicrobial) .

If resistance to TMP/SMX occurs or is suspected from recent use of this drug (bacterial resistance to sulfonamides occurs fairly quickly) or an allergy to sulfa is present, nitrofurantoin is an excellent choice. Bacterial resistance to nitrofurantoin develops very slowly (it should be noted, however, that protei have a natural resistance to nitrofurantoin), and prolonged therapy does not alter normal intestinal flora. Fluoroquinolones are highly effective in the treatment of UTIs due to their broad spectrum of activity, excellent renal and urinary levels, and low incidence of side effects. However, their high cost should limit their use to those patients who cannot tolerate more conventional medications or who have proven or suspected resistant bacteria.

Recurrent infections in women require urine culture and sensitivity testing. Most commonly, reinfection is responsible. Some women can correlate certain antecedent events, such as sexual activity or menses, with onset of their UTIs. These women usually will remain infection-free with the use of an antimicrobial just prior to sexual activity or during the onset of menses. Nitrofurantoin, trimethoprim, or TMP/SMX are excellent choices in these circumstances. Such women also should be advised to void after sexual activity to decrease the risk of bacterial cystitis.

If no clear historical reason for the reinfections can be elicited, antimicrobial prophylaxis can be instituted. One of the previously mentioned medications, such as nitrofurantoin, trimethoprim, or TMP/SMX, can be taken each night at bedtime for three to six months or more. This will allow eradication of pathogenic bacteria from the main reservoirs (vagina and colon). The use of fluoroquinolones for prophylaxis has not shown any advantage over conventional therapy.

• Why do uncomplicated Urinary tract infections occur?

In clinical practice, this question usually is raised by the young woman who asks, "If there is really nothing wrong, why do I suffer from these frequent infections?" Although the answer remains somewhat conjectural, research into the pathogenesis of UTIs has indicated a number of potential contributing bacterial and host factors.

Most infectious disease experts agree upon an ascending or retrograde route of bacterial infection. In women, progressive colonization of the perineum and vagina by bacteria with specific virulence properties occurs first. Such bacteria seem to possess an increased ability to adhere to mucosal surfaces. Microscopically, these pathogenic bacteria are coated with long, filamentous protein appendages, called "pili," which bind to receptors on host epithelial cells.

Research also has demonstrated that vaginal and urethral epithelial cells from women with recurrent infections may possess increased numbers of receptor sites for such bacteria as E. coli. With the observation that such receptors exist even on buccal mucosal cells in the same women, a genotypic trait for epithelial cell receptivity may represent a true susceptibility factor for UTIs. These receptors, which allow mechanisms that take place on a molecular level, may provide the first clues as to how fecal flora that colonize the vaginal introitus ascend into the urethra and gain access to the bladder.

Women also are particularly susceptible to UTIs for anatomic reasons. The proximity of the urethra to the anus, its location within the labia, and its relatively short length (4 cm) allow for colonization of the urethra with gram-negative bacilli. Urethral manipulation during sexual intercourse can lead to bacterial colonization of the urethra and bladder. Thus, urination after intercourse reduces the incidence of UTIs.

Vaginal mucus may hinder or help bacterial adherence. For example, vaginal colonization by lactobacilli and premenopausal levels of circulating estrogens lower vaginal pH and decrease bacterial adherence.

On the other hand, alteration of perineal flora by antimicrobial therapy and/or spermicides and a decline in circulating estrogen levels (such as with the onset of the menstrual cycle or with menopause) may lead to alkalinization of the vaginal fluid, overgrowth of gram-negative organisms, and an increase in bacterial-epithelial binding. Studies have demonstrated that the application of topical estrogens in postmenopausal women can increase lactobacillus counts, acidify vaginal fluid, and reduce the incidence of UTIs.

• What are the more serious forms of Urinary tract infections?

The diagnosis of acute pyelonephritis usually is made on the basis of clinical findings. The presence of fever, flank pain, chills, nausea, and malaise suggests renal parenchymal inflammation. A urinalysis and culture should be obtained on all patients. The presence of pyuria and white blood cell casts is consistent with pyelonephritis. The culture generally will grow E. coli, although often in numbers fewer than 105 CFUs/mL.

Management will depend on the clinical assessment of severity. Many patients can be treated in an ambulatory setting with TMP/SMX or a fluoroquinolone for 14 days. Defervescence and improvement should occur within three days; follow-up cultures should be performed at two weeks, since this is when relapse is most likely. Radiographic studies are not absolutely necessary, unless an underlying anatomic problem is suspected.

At times, the degree of illness requires hospitalization for monitoring and parenteral therapy. A second- or third-generation cephalosporin, fluoroquinolone, or the combination of gentamicin and ampicillin are appropriate initial antimicrobials. Oral therapy can be instituted when the patient is afebrile and has begun oral hydration. If symptoms and fever persist for more than 72 hours, an imaging study should be obtained. Computed tomography of the retroperitoneum with and without contrast will diagnose a renal or perirenal abscess, calculus, or anatomic abnormality.

Renal and perirenal abscesses deserve special mention. Although neither condition is associated with a unique set of signs or symptoms, the persistence of clinical pyelonephritis beyond three days should suggest the possibility of a pyogenic process. Patients who have diabetes, neurogenic bladder, or calculi and those who are pregnant are at higher risk for an abscess. Gram-negative bacteria (E. coli and protei) are the most common causative organisms, but staphylococci may seed the kidney hematogenously. Small abscesses (<3 cm) can be managed with antimicrobial therapy alone for six weeks, but larger lesions require percutaneous drainage as well.

Reduce your risk of urinary tract infections Most UTIs are not linked to sex. UTIs occur when microorganisms, usually bacteria from the digestive tract, cling to the opening of the urethra and begin to multiply....

Urinary tract infection Development Not everyone who develops a UTI has symptoms, but most people get at least some. See a doctor if you have any of these symptoms....

Last updated Jan 4/07