UTIs have been classified as acute or chronic, hospital-acquired (nosocomial) or community-acquired, uncomplicated or complicated, upper (pyelonephritis) or lower (cystitis, urethritis, prostatitis), symptomatic or asymptomatic, and de novo or recurrent.

The term urinary tract infection refers to the invasion of the urinary tract by a nonresident infectious organism. Bacteriuria denotes the presence of bacteria in the urine, which may be symptomatic or asymptomatic. Pyuria signifies the presence of white blood cells in the urine, an inflammatory response to bacterial invasion. Complicated UTI indicates a urinary tract infection that occurs in a patient with a structural or functional abnormality of the genitourinary tract (Table 1). These abnormalities predispose a person to UTIs through interference with the drainage of urine or through the formation of a nidus in which bacteria can grow.

In 1995, a National Institutes of Health/National Institute of Diabetes and Digestive and Kidney Diseases consensus established the prostatitis classification. Category I prostatitis is an acute bacterial prostatitis that presents with sudden and usually severe onset of symptoms. Category II refers to chronic bacterial prostatitis, which usually manifests as recurrent UTIs in older men. The causative organism is usually pansusceptible to antimicrobial agents. Again, it is important to bear in mind that only 5% of men diagnosed with prostatitis have evidence of infectious etiology.

The infection spreads to the urinary tract either through an ascending route, from the fecal reservoir through the urethra into the bladder, particularly in patients with intermittent or indwelling catheters; hematogenously, secondary to Staphylococcus aureus bacteremia; or by direct extension from adjacent organs via the lymphatic system, as in the case of retroperitoneal abscesses or severe bowel obstruction.

Escherichia coli is the most common infecting organism in patients with uncomplicated UTIs.⁸ Other gram-negative microorganisms causing UTIs include Proteus, Klebsiella, Citrobacter, Enterobacter, and Pseudomonas spp. Gram-positive pathogens such as Enterococcus faecalis, Staphylococcus saprophyticus, and group B streptococci can also infect the urinary tract. Other microorganisms such as Chlamydia and Mycoplasma spp have been known to cause UTIs in both men and women, but these infections tend to remain limited to the urethra and reproductive system. Chlamydia and Mycoplasma organisms may be sexually transmitted, so infections require treatment of both partners.

The ureters and bladder normally prevent urine from backing up toward the kidneys, and the flow of urine from the bladder helps wash bacteria out of the body. In men, the prostate gland produces secretions that slow bacterial growth. In both sexes, immune defenses also prevent infection. Despite these safeguards, infections still occur.

Some people are more likely to get UTIs than others due to host factors or urothelial mucosa adherence to the mucopolysacharide lining.⁹ Any abnormality of the urinary tract that obstructs the flow of urine (eg, kidney stones or an enlarged prostate) sets the stage for an infection. In addition, catheters, tubes, or foreign bodies in the bladder are common sources of infection. This increases the risk of UTIs in unconscious, critically ill patients who often need a catheter that stays in place for a long time. People with diabetes also have a higher risk of UTIs because of changes in their immune system, and any disorder that suppresses the immune system raises the risk of a UTI. Sexual intercourse⁵ and women's use of a diaphragm¹⁰ have also been linked to an increased risk of cystitis. Hormonal changes and shifts in the position of the urinary tract during pregnancy make it easier for bacteria to travel up the ureters to the kidneys. For this reason, many doctors recommend periodic testing of urine in pregnant women.

UTIs may be asymptomatic. However, some patients report incontinence and/or a general lack of well-being.¹¹ Pyelonephritis is a clinical syndrome characterized by flank pain, fever, chills, irritative voiding symptoms, and pyuria. Sometimes it presents with upper gastrointestinal symptoms such as nausea and vomiting. Cystitis and lower UTIs clinically manifest irritative voiding symptoms that include frequency, dysuria, urgency, and incontinence. In men, urinary retention should be ruled out, as it is frequently associated with UTIs.

Physical examination, including pelvic exam, should be carried out in women with lower urinary tract symptoms, to exclude gynecological, neurological or colorectal disorders. Physicians should also maintain a high index of suspicion for underlying sexually transmitted disease. Up to 50% of women presenting to an emergency department for symptoms of UTI, were found to have positive STD cultures.¹²

Urinalysis
Urine samples are collected in a sterile container through suprapubic aspiration; urethral catheterization, especially in women; or by midstream voided urine after the genital area is washed to avoid contamination. The sample is then tested for bacteriuria, pyuria, and hematuria. Indirect dipstick tests are informative but are less sensitive than microscopic examination of the urine. About one third of the women who have acute symptoms of cystitis have either sterile urine or some other cause for the symptom.¹³ Many diseases of the urinary tract produce significant pyuria without bacteriuria. These include staghorn calculi, tuberculosis, and infections caused by Chlamydia and Mycoplasma spp. Microscopic hematuria is found in 40% to 60% of cystitis cases.¹⁴ Associated gross hematuria should be evaluated further by imaging studies. Cystoscopy is indicated in those patients who are more than 50 years old or have other risk factors for concomitant diseases such as nephrolithiasis or transitional cell carcinoma (eg, smoking).

Urine Culture and Sensitivity Test
Bacteria are cultured and tested against different antibiotics to determine the drug that best destroys the bacteria. It is important to bear in mind that a large percentage of women with lower UTIs have been found to have sexual transmitted diseases (STDs). Additional cultures for Neisseria gonorrhea, Chlamydia, Mycoplasma hominis and Ureaplasma urealyticum should be considered for women with recurrent lower UTIs.

Imaging Techniques
Radiologic studies are unnecessary for the routine evaluation of patients with UTIs; however, they may be indicated to find the cause of complicated cases, where UTIs are associated with urinary calculi, ureteral strictures, ureteral reflux, urinary tract tumors, and urinary tract diversions. Helpful imaging techniques include:

• Plain radiograph of the abdomen for detection of radiopaque calculi or abnormal renal contour.
• Intravenous pyelogram for radiographic images of the bladder, kidneys, and ureters. An opaque dye visible on radiographic film is injected into the vein, and series of radiographs are taken. The films show an outline of the urinary tract, revealing even small changes in the structure of the tract. They are used to determine the site and extent of urinary tract obstruction.
• Voiding cystourethrogram for evaluation of the neurogenic bladder and urethral diverticulum, and to exclude or define the presence of vesicoureteral reflux.
• Renal ultrasonography, through the interpretation of the echo patterns of sound waves bounced back from internal organs. One can detect the presence of hydronephrosis, pyonephrosis, and perirenal abscesses. This technology poses no risk of radiation or intravenous contrast.
• Computed tomography (CT), a more sensitive method for defining renal as well as suprarenal pathology, especially when intravenous contrast is used. Spiral CTs of the abdomen and pelvis without contrast are extremely sensitive in identifying calculi within the collecting system, and have become standard practice as part of the acute flank pain protocol at our institution.
• Cystoscopy: through the use of fiberoptics, the urethra and the bladder can be inspected quickly and safely with a local anesthetic in an office setting.

For general management of UTIs, (Figure 1) the patient is advised to drink plenty of water, which helps cleanse the urinary tract of bacteria. Cranberry juice and vitamin C (ascorbic acid) supplements inhibit the growth of some bacteria by acidifying the urine. Avoiding coffee, alcohol, and spicy foods is also useful. A heating pad and pain relief medication are helpful for pain management.

UTIs are treated with antibacterial drugs. The choice of drug and length of treatment depend on several factors (Table 2). The sensitivity test is especially useful in selecting the most effective drug.

Acute Uncomplicated Cystitis
Patients who have symptoms of frequency, urgency, pyuria upon microscopic examination, and no known functional or anatomic abnormality of the genitourinary tract may be presumed to have acute uncomplicated cystitis. Empirical therapy with a 3-day regimen of trimethoprim/sulfamethoxazole (TMP-SMZ) or a fluoroquinolone without pretreatment culture and sensitivity testing is usually effective. Alternative regimens such as a fluoroquinolone, an oral third-generation cephalosporin, or nitrofurantoin (7-day regimen) may have a better result.

Recurrent Cystitis
Recurrent episodes of uncomplicated cystitis can be managed through several strategies. Behavioral therapy includes increasing fluid intake, urinating as soon as the need is felt as well as immediately after intercourse, and changing the method of contraception (for users of a diaphragm or spermicide). Long-term antimicrobial prophylaxis,¹⁵ postcoital prophylaxis with a single-dose antibiotic,¹⁶ or short-course (1- or 2-day) antibiotics for each symptomatic episode is recommended. For postmenopausal women, the use of vaginal estrogen cream may prove an effective preventive measure.¹⁷

Uncomplicated Pyelonephritis
Patients usually present with mild to severe flank pain, low- or high-grade fever, tenderness of the costovertebral angle on the infected side, or cystitis like symptoms. Urine cultures and sensitivity tests are needed for the diagnosis. 10 to 14 days of appropriate oral antimicrobial therapy is usually effective. If the patient presents with fever, nausea, and vomiting, he or she can be rehydrated and then given a single dose of a parenteral agent, after which an oral antimicrobial is prescribed. A urine culture should be obtained 1 to 2 weeks after treatment to verify the cure.

Prostatitis
Prostate infections are harder to cure because antibiotics are unable to penetrate infected prostate tissue effectively. For this reason, men with acute bacterial prostatitis often need long-term treatment (at least 30 days) with a carefully selected antibiotic. Severely ill patients need hospitalization and parenteral antimicrobial agents such as an aminoglycoside-penicillin combination. In men with urinary retention, a urethral or suprapubic catheter is necessary. Mild and moderate cases respond well to fluoroquinolones or TMP/SMZ, both of which have a cure rate of 60 to 90%.¹⁸ Chronic bacterial prostatitis has episodes of recurrent bacteriuria with the same organism between asymptomatic periods. Episodic treatment may be prescribed using the agents mentioned above, and in selected patients, may be self-prescribed as needed. Daily suppressive therapy should be considered in men with frequent UTIs if other causes are excluded and the culpable organism is localized to the prostate, using the Meares-Stamey technique.¹⁹

Complicated UTIs
These patients present with signs of sepsis, hypotension, temperature > 40°C, a tender subcostal angle, or intractable nausea and vomiting. They are more likely to have functional, metabolic, or anatomic abnormalities of the urinary tract. Pretreatment cultures and sensitivity testing should be obtained, and a full course of appropriate antimicrobial therapy should be given. Severely ill patients may be hospitalized until they can ingest fluids and take medication on their own. Blood cultures should also be obtained. Complete investigation of the upper and lower urinary tract are recommended to assure that there are no stones, hydronephrosis, or abscess. A follow-up urinalysis helps to confirm that the urinary tract is infection free. Kidney infections generally require several weeks of antibiotic treatment.

Sexually Transmitted Diseases
Special cultures are needed to diagnose these infections. Antibiotic therapy should be prescribed accordingly. Longer treatment with tetracycline, doxycycline, or any drug appropriate for the treatment of Chlamydia, Mycoplasma hominis and Ureaplasma urealyticum is recommended.²⁰

Catheter-related Infections
Catheterization for more than 2 weeks is usually associated with bacteriuria. Prophylactic antimicrobial therapy for UTIs during short-term, indwelling, urethral catheterization is not recommended. Short-term antimicrobial therapy (5 to 7 days) is indicated only in symptomatic episodes. Removal of an indwelling catheter should be prompt; whenever possible, intermittent self-catheterization should be used in patients with transient or long-term urinary retention.

Asymptomatic Bacteriuria
Treatment of asymptomatic bacteriuria is indicated in pregnant women and in those requiring urologic surgery.²¹ Preoperative treatment reduces postoperative complications, including bacteremia.²²

Infections in Pregnancy
The presence of asymptomatic bacteriuria in a pregnant woman should be treated promptly with a 7-day regimen of ampicillin or nitrofurantoin. Pregnant women are not more susceptible to cystitis; however, the risk of pyelonephritis and cystitis can lead to premature delivery of the baby, low birth weight, pyelonephritis, and high blood pressure.²³

Urinary Tract Infection with Renal Failure
When creatinine clearance is significantly impaired, antibiotic dosage should be decreased since the renal blood flow is decreased and the perfusion of antimicrobial agents into the renal tissue and urine is impaired. Ampicillin, TMP/SMZ, and fluoroquinolones are all effective in the treatment of UTI in uremic patients.^23,24 Nitrofurantoin and tetracyclines are contraindicated for the treatment of UTIs in uremic patients.

Prophylaxis
Antimicrobial prophylaxis is recommended to ensure the sterility of urine for those who appear susceptible to developing infections. These include immunocompromised patients, patients with heart disease, people with a prosthetic heart valve, and patients who are scheduled for a procedure eg, cystoscopy. Oral or vaginal estrogen administration prophylactically to postmenopausal women also reduces the symptoms of cystitis.^21,25

UTI is one of the most common health problems affecting all ages. It is the most common nosocomial, bacterial infection in the elderly. Women are especially prone to UTIs for reasons that are poorly understood. Although prostatitis syndrome accounts for 25% of male office visits for genitourinary tract infections, only 5% are attributed to a bacterial cause. Acute cystitis or pyelonephritis in adult patients should be considered uncomplicated if there are no known functional or anatomic abnormalities of the genitourinary tract. Most of these infections are caused by Escherichia coli. Acute uncomplicated cystitis can be effectively treated with a 3-day course of TMP/SMZ, but alternative regimens such as a fluoroquinolone, an oral third-generation cephalosporin, or nitrofurantoin (7-day regimen) may have a better result. For acute uncomplicated pyelonephritis, a 10- to 14-day regimen is recommended. Sexually transmitted diseases including those caused by Chlamydia, Mycoplasma hominis and Ureaplasma urealyticum should be considered potential culprits in sexually active patients. Complicated UTIs require thorough evaluation and correction of the underlying abnormality in order to provide a cure and to prevent recurrence.

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