Joseph B. Abdelmalak,
MD, Sandip P. Vasavada,
MD, and Raymond R. Rackley,
MDCONTENTS
INTRODUCTION
CLASSIFICATION/TERMINOLOGY
ROUTESOF INFECTION
URINARY PATHOGENS
RISK FACTORS
DIAGNOSIS
TREATMENT
SUMMARY
REFERENCES
INTRODUCTION
Urinary tract infection (UTI) is a common health problem affecting millions of people each year. They are the most common nosocomial infections and are second in serious- ness only to respiratory infections. UTIs account for more than 7 million physician visits every year in the United States alone (1). They are the most common bacterial infection found in the elderly and the most frequent source of bacteremia (2,3). The incidence ratio of UTIs in middle-aged women to men is 30:1. However, during later decades of life, the incidence of infection in women to men decrease. Women are especially prone to UTIs for reasons that are poorly understood. One factor may be that a woman’s urethra is short, allowing bacteria quick access to the bladder. Also, a woman’s urethral opening is near sources of bacteria from the anus and vagina. For many women, sexual intercourse seems to trigger an infection, although the reasons for this linkage are unclear (4). In men, prostatitis syndromes account for about 25% of office visits for genitourinary tract infections (5). Five percent of these men have bacterial prostatitis, 64% have nonbacte- rial prostatitis, and 31% suffer from pelviperineal pain syndrome (6).
CLASSIFICATION/TERMINOLOGY
UTIs have been classified as acute or chronic, hospital-acquired (nosocomial) or community-acquired, uncomplicated or complicated, upper (renal) or lower (bladder, urethra, prostate), symptomatic or asymptomatic, and de novo or recurrent.
The term UTI refers to the invasion of the urinary tract by a nonresident infectious organism. Bacteriuria implies the presence of bacteria in the urine and may be symptom- atic or asymptomatic. Pyuria signifies the presence of white blood cells in the urine, an inflammatory response to bacterial invasion. Complicated UTI indicates a UTI that occurs in a patient with a structural or functional abnormality of the genitourinary tract (Table 1). These abnormalities predispose a person to UTI through interference with the drainage of urine or through the formation of a nidus in which bacteria can grow.
ROUTES OF INFECTION
The infection spreads to the urinary tract either through the ascending route from the fecal reservoir through the urethra into the bladder particularly in patients with intermit- tent or indwelling catheters, hematogenous route secondary to staphylococcus aureus bacteremia, or direct extension route from adjacent organs via lymphatic as in case of retroperitoneal abscesses or severe bowel obstruction.
URINARY PATHOGENS
Escherichia coli is the most common infecting organism in patients with uncompli- cated UTIs (7). Other Gram-negative micro-organisms causing UTIs include Proteus, Klebsiella, Citrobacter, Enterobacter, and Pseudomonas spp. Gram-positive patho- gens, such as Enterococcus faecalis, Staphylococcus Saprophyticus, and group B Strep- tococci, can also infect the urinary tract. Other micro-organisms called Chlamydia and Mycoplasma have been known to cause UTIs in both men and women, but these infec- tions tend to remain limited to the urethra and reproductive system. These organisms may be sexually transmitted, so infections require treatment of both partners.
RISK FACTORS
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
Table 1
Functional and Structural Abnormalities of the Genitourinary Tract
Functional abnormalities Obstruction Other
• Vesicoureteral reflux • Congenital abnormalities • Diabetes mellitus
• Neurogenic bladder • Renal cysts • Renal failure
• Pelviureteric obstruction • Urinary diversions Foreign bodies • Ureteric and urethral strictures • Urinary instrumentation
• Indwelling catheters • Urolithiasis
• Nephrostomy tubes • Bladder diverticuli
• Ureteric stents • Tumors
prostate gland produces secretions that slow bacterial growth. In both sexes, immune defenses also prevent infection. Despite these safeguards, however, infections still occur. Some people are more prone to getting UTIs than others because of host factors such as alter urothelial mucosa adherence mucopolysacharide lining (8). Any abnormal- ity of the urinary tract that obstructs the flow of urine (e.g., kidney stone, 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 the immune system. Any such disorder that suppresses the immune system raises the risk of a UTI. Sexual intercourse (4) and women who use a diaphragm (9) 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.
DIAGNOSIS
UTIs may be asymptomatic. However, some patients report symptoms of inconti- nence and/or a general lack of well-being (10). Pyelonephritis is a clinical syndrome characterized by flank pain, fever, chills, irritative voiding symptoms, and pyuria. Some- times it presents with upper gastrointestinal symptoms, such as nausea, and vomiting.
Cystitis and lower UTIs have the clinical manifestations of irritative voiding symptoms, including frequency, dysuria, urgency, and incontinence.
Urinalysis
Urine samples are collected in a sterile container through suprapubic aspiration, ure- thral catheterization especially in females, or by midstream voided urine after washing the genital area to avoid contamination. The sample is then tested for bacteruria, pyuria, and hematuria. Indirect dipstick tests are informative but are less sensitive than micro- scopic examination of the urine. About one-third of the women who have acute symp- toms of cystitis have either sterile urine or some other cause for the symptom (11). Many diseases of the urinary tract produce significant pyuria without bacteruria. These include staghorn calculi, tuberculosis, chlamydia, and mycoplasma. Microscopic hematuria is found in 40–60% of cystitis cases (12). Associated gross hematuria should be evaluated further via imaging studies. Cystoscopy in those patients who are over 50 yr and/or have other risk factors for concomitant diseases, such as nephrolithes or transitional cell carcinoma (i.e., smoking).
Urine Culture and Sensitivity Test
Bacteria is 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 percent of female with lower UTIs have been find to have sexually transmitted diseases. Additional cul- tures for Gonococcus, Chlamydia, urea plasma, and Mycoplasma should be considered.
Imaging Techniques
Radiologic studies are unnecessary for routine evaluation of patients with UTIs;
however, they may be indicated to find out the cause of complicated cases. These are the
cases where UTIs are associated with urinary calculi, ureteral strictures, ureteral reflux, urinary tract tumors, and urinary tract diversions. Helpful imaging techniques include the following:
• Plain x-ray film of the abdomen for detection of radiopaque calculi, or abnormal renal contour.
• Intravenous pyelogram that gives x-ray images of the bladder, kidneys, and ureters. An opaque dye visible on x-ray film is injected into the vein, and series of x-rays 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 the evaluation of neurogenic bladder, urethral diverticu- lum, and to exclude or define 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 nor intravenous contrast.
• Computed tomography (CT), a more sensitive method to define renal as well as supra- renal pathology, especially when intravenous contrast is used. Spiral CT of the abdomen and pelvis with or without contrast are extremely sensitive in identifying calculi within the collecting system, and have become standard practice as part of acute flank pain protocol at Cleveland Clinic Foundation.
• Cystoscopy, through the use of fiberoptic, the urethra and the bladder can be inspected quickly and safely with local anesthetic on an office setting.
TREATMENT
General management of UTIs includes drinking plenty of water, which helps cleanse the urinary tract of bacteria. Taking cranberry juice and vitamin C (ascorbic acid) supple- ments inhibit the growth of some bacteria by acidifying the urine. Avoiding coffee, alcohol, and spicy foods is also useful. 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 with the symptoms of frequency, urgency, pyuria upon microscopic exami- nation, and no known functional or anatomical abnormality of the genitourinary tract
Table 2
Factors Influencing the Selection of Antimicrobial Agents in Treating UTI
Patient Drug Organism
• History of drug allergy • Safety profile • Gram’s-stain
• Medical history • Spectrum of activity • Special culture
(renal impairment, liver impairment) • Route of administration
• Concomitant medication • Costs
• Presence of urological abnormalities