Diagnosis and Management of Urinary Tract Infections: A Disease Stratification M
Diagnosis and Management of Urinary Tract Infections: A Disease Stratification Model
Part I: Epidemiology, Detection, and Evaluation
Author: Scott A. Gallagher, MD, Staff Physician, Department of Emergency Medicine, Aspen Valley Hospital, Aspen, CO.
Peer Reviewer: Robin R. Hemphill, MD, Assistant Program Director, Emergency Medicine Residency, San Antonio Uniformed Services Health Educator Consortium, Fort Sam Houston, TX; Assistant Professor, Department of Emergency Medicine, Vanderbilt University, Nashville, TN.
Urinary tract infection (UTI) is an extremely common diagnosis among patients evaluated in the emergency department (ED). Each year in the United States, UTIs result in more than 7 million physician visits, complicate or necessitate more than 1 million hospital admissions, and use more than $1 billion of our national health care expenditure.1-3 The majority of these infections occur in otherwise healthy young women who present with symptoms of acute uncomplicated bacterial cystitis or pyelonephritis. These patients are at low risk for occult genitourinary tract abnormalities and predictably respond to empiric antibiotic therapy initiated by the ED physician. Certain patient populations, however, have complicating conditions that increase the risk for acquiring infection or failing therapy. Complicated UTIs may occur in men, children, pregnant women, elderly or immunocompromised patients, and those with neurologic disorders. Infection in these settings ranges from mild cystitis to life-threatening urosepsis, and may be more difficult to treat because of associated structural or functional genitourinary tract abnormalities, resistant organisms, or inadequate host defenses. Special consideration must be given to this group of patients who require prompt, appropriate therapy and evaluation to avoid prolonged infection or serious sequelae in the setting of UTI. Therefore, it is essential that the ED physician be familiar with the evaluation, diagnosis, and management of urinary tract infections. This model presents a comprehensive review of this common clinical entity.
—The Editor
Epidemiology
Females. UTIs are a significant health problem in the United States, affecting all ages and both sexes, although not equally. Except in neonates and infants, the prevalence and incidence of UTIs are much greater in females. UTIs in women outnumber men by a ratio of 30:1, and as many as 50% of adult females report having a UTI at some point in their lifetime.4 Up to 50% of those women with initial infection will develop a recurrent infection. While there is no significant, long-term morbidity associated with uncomplicated UTI in otherwise healthy women, patients experience discomfort, missed days from school or work, and restricted activity. The cost of evaluation and treatment of ambulatory women with dysuria, not including the many who require hospitalization, is estimated to be nearly $1 billion annually.5
For women who are pregnant, UTI is the most common infectious complication, resulting in five times as many febrile episodes as viral infections.6 Bacteriuria in pregnancy carries a much greater risk of progressing to pyelonephritis than in non-pregnant women (28% vs 1.4%) and is associated with serious risks and significant treatment costs.6
Males. In males older than age 50, UTI occurs at an incidence approaching that of age-matched women, presumably as a result of prostatic disease. However, among ambulatory patients in this age group, infection in women still outnumbers men by a margin of approximately 2:1. In institutionalized and hospitalized patients, however, there appears to be no significant difference in the prevalence of UTIs between elderly men and women.7
UTI is actually more common in male neonates and infants than females for approximately the first 6-12 months of life.4,7,8 Infection in neonatal boys outnumbers girls approximately 5:1. By preschool age, the sex ratio becomes reversed, with the majority of UTIs occurring in females. UTIs are one of the most common serious bacterial infections among febrile pediatric patients, both boys and girls, with a reported prevalence ranging from 4.1% to 7.5%.8 Recurrence is common and occurs in approximately 18% of male and 26% of female infants.9 Bacteriuria in young men is rare and has an estimated prevalence of less than 1% as compared to 13% seen in men older than 65 years of age. In elderly males, as well as females, bacteriuria is the most frequently documented bacterial infection, the most common nosocomial infection, and the most frequent cause of sepsis, although most deaths in these patients are generally associated with severe underlying disease.10-12
Definitions
Urinary Tract Infection. UTI is a general term referring to infection anywhere along the urinary tract from the urethral meatus to the kidneys. Structures in this pathway include the urethra, bladder, ureters, renal pelvis, and parenchyma. Associated structures that may also become infected and serve as foci of recurrent UTI are the prostate, epididymis, and perinephric fascia. UTI is defined by the presence of a significant quantity of bacteria in the urine in the setting of clinical signs and symptoms of infection.
Bacteriuria. Bacteriuria refers to the presence of bacteria in the urine and does not necessarily imply infection. Bacteriuria may be significant or nonsignificant, depending on the quantity of bacteria in the urine. Significant bacteriuria, implying infection, has traditionally been defined as a urine culture containing more than 105 colony-forming units (cfu) of an organism per mL. A lower threshold for treatment and diagnosis, however, is often applied to pregnant women with bacteriuria and men with suspected UTI. Similarly, in young women with dysuria, a urine culture demonstrating greater than 102 cfu/mL may have the best combination of sensitivity and specificity for making the diagnosis of acute cystitis.13
Bacteriuria may also be considered as either asymptomatic or symptomatic. Asymptomatic bacteriuria (ABU) is defined as significant bacteriuria in patients without the clinical symptoms of UTI.
Pyuria. Pyuria refers to the presence of white blood cells (WBC) in the urine and generally indicates a significant inflammatory response to bacteriuria, such as occurs with infection, but may also be present in the setting of asymptomatic bacteriuria without overt infection.
Hematuria. Hematuria refers to the presence of red blood cells in the urine. The presence of hematuria is of differential value in young women with the complaint of dysuria, as it is common with UTI but not urethritis or vaginitis. The presence of hematuria does not imply a complicated infection unless it fails to clear once the infection has been eradicated.
Recurrent UTI. Recurrent UTI is defined as two or more infections over a six-month period. This is in distinction to isolated or remotely recurring UTIs, which refer to first infections or those separated from the previous infection by at least six months. Recurrent UTIs are divided into two categories: reinfection and bacterial persistence. Reinfection represents approximately 95% of recurrent UTIs in women and refers to a new infection from a point outside of the urinary tract following initial successful sterilization of the urine. This is distinct from bacterial persistence in which later infection arises from a persistent focus within the urinary tract with the identical organism previously eradicated.
Upper vs. Lower UTI. Lower tract infections include urethritis, an infection limited to the urethra, and cystitis, an infection confined to the bladder. Upper tract infections include ureteritis and pyelitis; infections extending from the bladder into the structures of the upper collecting system (ureters and renal pelvis); and pyelonephritis, a more extensive infection extending into the renal parenchyma. This distinction among upper tract infections may be important, particularly in children, where pyelonephritis has the potential for irreversible renal parenchymal damage.
Complicated vs. Uncomplicated UTI. UTIs are considered complicated or uncomplicated based upon the presence or absence of conditions that increase the risk for acquiring infection or failing therapy. Uncomplicated UTIs generally occur in patients with intact host defenses, including a functionally and structurally normal urinary tract and competent immune system. This distinction between complicated and uncomplicated UTI is important because of implications regarding the potential for morbidity, as well as the type and extent of treatment and evaluation needed.
For example, acute bacterial cystitis occurring in an otherwise healthy, nonpregnant adult female is generally considered uncomplicated. There is little to no potential for long-term or serious morbidity and it requires only an abbreviated evaluation and short-course of treatment. Similarly, in selected patients, acute pyelonephritis may be considered "uncomplicated,"—despite the fact that it involves the upper urinary tract—when no complicating conditions are present. Cystitis and pyelonephritis are considered complicated when they occur in the setting of any condition that increases the risk for acquiring infection, failing therapy, or having long-term or serious morbidity. In males, it is conventional to consider all UTIs as complicated because most of them occur in children or the elderly and are associated with genitourinary tract abnormalities, bladder outlet obstruction, or instrumentation. A small number of these infections, however, occur in healthy, young men with certain behavioral risk factors and should be considered uncomplicated.
Pathophysiology
Bacteriology. Infection occurs as a result of interactions between host defenses and uropathogens. Increased bacterial virulence appears to be necessary to overcome strong host defenses in the healthy patient, whereas bacteria with minimal virulence are able to infect patients whose defenses are significantly compromised. Certain bacterial strains selectively result in UTIs. (See Table 1.) This occurs not by chance or based on prevalence, but because of the presence of specific virulence factors that enhance adherence and colonization to the uroepithelium by these uropathogenic bacteria. Most uncomplicated UTIs are caused by the single, large family of gram-negative, aerobic bacilli found in the gastrointestinal tract known as Enterobacteriaceae. Included in this family are the Escherichia, Klebsiella, Enterobacter, Citrobacter, Proteus, Providencia, Morganella, Serratia, and Salmonella species. By far, Escherichia coli is the dominant pathogen in both men and women, accounting for approximately 85% of community-acquired and 50% of nosocomial UTIs. Anaerobic fecal flora rarely produce infection, despite being 100-1000 times more abundant than E. coli in stool. Other common pathogens include the gram-positive organisms S. epidermidis, S. saprophyticus, and Enterococcus species, which presumably result in UTI following colonization of the vaginal or perineal skin. Less common organisms, such as Gardnerella vaginalis, Mycoplasma species, and Ureaplasma urealyticum may infect patients with intermittent or indwelling catheters.14 Resistant organisms may be seen in hospitalized patients as a result of the use of broad-spectrum antibiotics.
| Table 1. Urinary Pathogens45 |
| Community-Acquired |
Escherichia coli |
| Hospital-Acquired |
Escherichia coli_____________________________________________ |
Route of Infection. Infectious organisms may gain entry to the urinary tract through two primary mechanisms: ascending and hematogenous routes. The ascending route is the primary route of entry in nearly all UTIs. Bacteria enter the urinary tract from the fecal reservoir via ascent through the urethra into the bladder and, in the case of pyelonephritis, up the ureter to the kidney. Colonization of the urethra occurs commonly in females, uncircumcised males, and catheterized patients. The female urethra is susceptible to colonization with rectal uropathogens because it is short, it is surrounded by the moist mucosa of the vaginal introitus, and the meatus is in close proximity to the perirectal area. The male urethra is longer and located considerably farther from the perineum and anus, and, except in the uncircumcised male infant, the meatus is surrounded by the dry epithelium of the glans penis, which is less encouraging to bacterial growth. It is generally believed that these anatomic differences account for the higher incidence of UTI in females of nearly all age groups. Indwelling catheters provide a conduit for bacteria along their external and internal surfaces and have been demonstrated to have organisms contained within a biofilm, well protected from antibiotics and the flow of urine. Once bacteria are introduced into the ureter or bladder they may ascend to the kidney unaided. Reflux of urine is not required for ascending infections, but edema associated with cystitis may cause sufficient changes in the ureterovesical junction to permit reflux. This ascent, however, is greatly increased if the bacteria have special adhesion properties (i.e., P-fimbriae of E. coli) or by any process that interferes with the normal ureteral peristaltic function. A possible exception to the concept that the ascending route is the primary route of infection may be in newborn infants. Although controversial, it has been suggested that in neonates, a predominantly hematogenous route is responsible for UTIs because of the higher incidence of bacteremia observed by some in this age group as compared with older infants.15,16 A third route, the lymphatic route, results in UTI when there is direct extension of bacteria from the adjacent organs via lymphatics. This may occur in unusual circumstances, such as severe bowel infection or retroperitoneal abscess, and there is little evidence that this route plays a significant role in the vast majority of UTIs.
Risk Factors
Women. Many factors have been historically attributed with an increased risk of UTI. (See Table 2.) In young women, factors traditionally considered to influence the risk of UTI have included the following: sexual intercourse ("honeymoon cystitis"), use of a diaphragm with spermicide, delayed postcoital micturation, ABO-blood-group nonsecretor phenotype, reduced water intake, decreased voiding frequency, direction of wiping after bowel movement, type of menstrual protection, use of vaginal deodorants, douching, occlusive underclothing, and frequency of perineal cleansing. In young, sexually active women, however, only recent sexual intercourse, recent use of a diaphragm with spermicide, and a history of prior UTI have been identified in large studies to be independently associated with increased risk for UTI.17 Coital frequency and diaphragm use show a dose-response relationship with the risk of developing UTI, with risk increasing with the frequency of activity. Intercourse is thought to facilitate migration of organisms up into the bladder following initial colonization of the vaginal and urethral mucosa with uropathogens. Spermicide use, with or without a diaphragm, and estrogen deficiency in postmenopausal women are thought to alter the normal vaginal environment in favor of uropathogens. The strongest risk factor for the development of UTI appears to be a history of prior UTI, although the mechanism is not clear. Possibilities may include a biologic predisposition among certain women (i.e., ABO-blood-group nonsecretor status or immune hyporesponsiveness to E. coli antigens) or persistent alterations in the vaginal flora that occur as a result of prior infection or antimicrobial treatment.18-22
| Table 2. Factors that may Influence the Risk of Urinary Tract Infection |
| Young Women |
Recent sexual intercourse |
| Postmenopausal Women |
Reduced bladder tone |
| Pregnancy |
Prior UTI |
| Young Men |
Anal intercourse |
| Older Men |
Bladder outlet obstruction |
| Children |
Uncircumcised male infants |
| Immunocompromised |
Advancing age_________________________________________________________ |
Pregnancy. Specific influences during pregnancy increase the risk for UTI. The most important of these influences is the mechanical effect the gravid uterus exerts on the ureters and bladder. As the uterus ascends above the level of the pelvic brim, the ureters become compressed and dilated while the bladder becomes congested and displaced from the pelvis into the abdomen. The right ureter is usually more dilated than the left, because of the common dextrorotation of the uterus. Additionally, elevated levels of progesterone and estrogen cause dilatation and decreased parastalsis of the ureters and bladder. Late in pregnancy, the bladder may contain double its usual volume without discomfort. The net result of these influences is to create a situation in which urine remains in the urinary tract longer than usual, providing an opportunity for bacteria to thrive and for one or both kidneys to become infected. Except in women with sickle cell disease, diabetes, or lower socioeconomic class, the prevalence of bacteriuria in pregnancy does not differ from age-matched, nonpregnant females. Bacteriuria in pregnancy has a 28% incidence of progression to pyelonephritis, however, as compared to 1.4% in nonpregnant females.6,23
Males. Young, healthy men rarely develop UTIs in the absence of complicating factors. When they do occur, they are usually associated with behavioral risk factors including anal intercourse, exposure to a colonized partner, or lack of circumcision. Infection occurs only when highly virulent strains enter the urethra and progress to infect the bladder or kidney. Such strains are more likely to enter the urethra in sexually active men whose female partners have vaginal colonization with E. coli or in homosexual men in which anal intercourse may facilitate urethral colonization. Uncircumcised males may have heavy colonization of the prepuce by gram-negative bacteria, particularly pathogenic fimbriated E. coli that adhere well to the mucosal surface of the prepuce.24,25 Uncircumcised male infants have a 10- to 20-fold increase in the incidence of UTIs as compared with females and circumcised male infants.26,27 In men older than 50 years of age, the prevalence of UTI approaches that of age-matched females, presumably as a result of prostatic disease, such as benign prostatic hyperplasia (BPH) and prostate cancer. Other causes include bladder cancer, urethral stricture, calculi, foreign bodies, phimosis, neurologic dysfunction, and catheterization.
Children. Elimination of bacteria from the bladder by frequent and complete bladder emptying is important in protecting against infection in children as well. Various types of voiding dysfunction have been correlated with UTIs in children, including infrequent or incomplete voiding, constipation, and vesicoureteral reflux. Commonly held misconceptions related to the causes of UTI include improper wiping techniques, bubble baths, and narrowed urethral caliber in girls. There is no evidence to support these myths. The strongest evidence against improper wiping techniques is that despite daily exposure to soiled diapers, the great majority of non-toilet-trained infants never develop UTI. Bubble baths may occasionally cause dysuria from local irritation; however, there is no proven association with cystitis. Narrowed urethral caliber is no longer thought to play a role in girls with UTI, and, consequently, urethral dilatation is not indicated in their management.8
Other. Instrumentation is a significant independent risk factor for the development of UTI in both sexes, with a 3-10% incidence of infection per day. An average, short-term hospital stay results in a 10-30% incidence of bacteriuria in patients with an indwelling catheter. Nursing home patients who are managed with long-term catheterization are nearly all bacteriuric by the end of 30 days. Duration of catheterization, therefore, is the most important risk factor for the development of bacteriuria and UTI. Other risk factors associated with UTI in catheterized patients include diabetes mellitus, female sex, elevated serum creatinine, periurethral or drainage bag colonization with uropathogens, errors in catheter care, absence of antibiotic use, catheterization other than for surgery or output measurement, and absence of a urine meter.28,29
Underlying medical illness is a significant risk factor for the development of UTI, presumably because of immunosuppression, such as occurs in HIV, diabetes, chemotherapy, and transplant patients. The prevalence of UTI in HIV-infected patients ranges from 8% to 50%.30 Additional risk factors in HIV include, CD4 counts of less than 200, intravenous drug use, indwelling urinary catheters, intravenous catheters, and antineoplastic and antiretroviral therapy. The causative agents in AIDS patients include a wide variety of gram-negative bacilli, gram-positive cocci, and opportunistic pathogens. Diabetic patients are also at risk of UTI and may develop severe complications, including renal and perirenal abscesses, gas-forming infections (emphysematous cystitis or pyelonephritis), fungal infections, xanthogranulomatous pyelonephritis, and renal papillary necrosis.31
Evaluation
History. The classic presentation of UTI in adults includes dysuria, frequency, urgency, nocturia, suprapubic discomfort, cloudy urine, and gross hematuria. Fever (> 38°C) is not characteristic of uncomplicated acute cystitis. In pregnancy, these symptoms are nonspecific as suprapubic discomfort, increased frequency, urgency, and nocturia are common even in the absence of infection during pregnancy. Dysuria, in pregnancy, is the most specific symptom of UTI.23 Young, sexually active, nonpregnant women may complain of dysuria in the setting of cystitis, urethritis, or vaginitis. Historical clues that suggest urethritis, or vaginitis include a partner with urethral symptoms, prior history of STD, vaginal discharge or odor, pruritus, dyspareunia, gradual onset of symptoms over several weeks, and no increased frequency or urgency.5 Acute pyelonephritis often presents with spiking fevers, shaking chills, nausea, vomiting, anorexia, and costovertebral pain.4 Flank pain is generally considered necessary to diagnose pyelonephritis; however, serious difficulties may arise in young children and spinal cord-injured patients who are unable to localize their symptoms. Similarly, elderly patients manifest few if any of the classic symptoms and signs of UTI. They are more likely to present with gastrointestinal complaints, such as nausea and vomiting, or abdominal pain and distension such as occur with bladder outlet obstruction or an obstructed urinary catheter. Very young children generally present only with nonspecific symptoms such as irritability, poor feeding, failure to gain weight, vomiting, and diarrhea. Neonates often do not mount a fever, although fever is present with UTI by the time children reach infancy (1-12 months of age).8
Physical examination. Physical examination of patients with suspected UTI should include palpation of the abdomen and flank and, occasionally, a genital examination. Abdominal examination may reveal suprapubic tenderness in cystitis or bladder distension in the setting of obstruction.4 Flank examination may reveal a bulging mass in patients with a perinephric abscess or costovertebral angle tenderness to palpation in patients with pyelonephritis. Genital examination in boys with UTI should be performed to document the circumcision status and exclude significant meatal stenosis or phimosis. In females, a pelvic examination is indicated if there is any suspicion for urethritis or vaginitis, or if there is doubt as to the diagnosis. Young females should be examined for labial adhesions that predispose the perineum to colonization and increase the likelihood for contamination of voided urine specimens. A history of voiding dysfunction in children should prompt a brief neurologic examination to evaluate for perineal sensation, peripheral reflexes in the lower extremities, and sacral dimpling or cutaneous abnormalities of the lower back. Abnormalities may suggest an underlying spinal abnormality, such as occult spinal dysraphism. Rectal examination should be performed if there is a history suggestive of fecal impaction, severe constipation, or encopresis in males to rule out prostatitis.
Urinalysis. Dipstick and microscopic urinalysis are commonly used rapid screening tests to detect the presence of pyuria, hematuria, and bacteriuria. The dipstick leukocyte esterase test has a sensitivity of 75-96% and specificity of 94-98% for detecting 8-10 leukocytes per high-power field (hpf) on microscopy.32,33 The positive predictive value of the leukocyte esterase test is 50%, and the negative predictive value is 92%.34 Factors affecting the number of leukocytes include urine flow, hydration status, and previous antibiotic therapy. The dipstick nitrite test has a sensitivity of only 35-85%, but a specificity of 92-100%.35 False-negative results occur because of use of diuretics, inadequate levels of dietary nitrate, or presence of bacteria that do not produce nitrate reductase, such as Staphylococcus, Enterococcus, or Pseudomonas.36 Centrifuged urine is suggestive of significant bacteriuria (> 105 cfu/mL) when there are more than 10 WBC/hpf. Even a single bacterium identified with Gram’s stained unspun urine under oil immersion is suggestive of significant bacteriuria. This finding has a sensitivity and a specificity approaching 90%.37 The presence of vaginal epithelial cells suggests specimen contamination and a new specimen should be obtained.
In certain populations, caution must be taken in interpreting the results of the urine dipstick test. In the elderly or catheterized population, for instance, positive results of leukocyte esterase or nitrite test do not necessarily indicate infection. These findings should not preclude further search for alternative sources of infection when acute urinary tract symptoms are not present. Without symptoms, asymptomatic bacteriuria is the most likely cause of positive dipstick tests. Dipstick and microscopic urinalysis are generally not considered adequate screening tools in pregnancy, while urine culture remains the standard screening test for bacteriuria. Similarly, in children, there is some controversy as to the best method of evaluating for UTI. The historical view is that the only way to accurately diagnose UTI in children is by urine culture. In some studies, leukocyte esterase tests have sensitivities as low as 53% and nitrite tests as low as 29%. This has led to the conclusion that dipstick urinalysis is an inadequate screening tool for children suspected of having UTI. A combined leukocyte and nitrite test on a single dipstick, however, has been reported to have an improved sensitivity of 78-92% and a specificity of 60-98%. Microscopic analysis, particularly with Gram staining, may be predictive enough to permit presumptive therapy. The "enhanced" microscopic analysis combines a hemocytometer reading of leukocyte count and standardized Gram-stained smear on uncentrifuged urine with improved sensitivity and positive predictive value for the identification of positive urine cultures in children. Findings of pyuria alone on this test (at least 10 leukocytes per mm3 on hemocytometer) has a sensitivity of approximately 89%. These findings suggest that it may be possible to eliminate the urine culture when the dipstick or enhanced urinalysis are negative and clinical suspicion is low.8
Urine culture. The definitive diagnosis of UTI requires the isolation of significant numbers of a single organism on urine culture. Specimens for urine culture should be obtained in all pediatric patients with positive urinalysis and when the clinical index of suspicion is high.8 Urine culture remains the most cost-effective and practical screening test for bacteriuria in pregnancy. Cultures are indicated in the management of all pregnant women with UTI, patients with pyelonephritis, and any complicated UTI. A sample obtained by clean-catch midstream urine is the standard collection technique for adults and older children. In young children, it is recommended that urine be obtained by bladder urethral catheterization using an 8 French feeding tube, or by suprapubic aspiration. In practice, the urine specimen is often initially obtained by applying a collection bag (U-Bag) to the perineum. Bag specimen collection, however, is not generally considered acceptable for specimen collection. This technique is associated with a high rate of contamination and, thus, is reliable only when results are negative. It is important that specimens be refrigerated immediately after voiding to minimize growth of contaminating bacteria. Polymicrobial growth strongly suggests contamination, and the specimen should be recollected. Other factors associated with the growth of multiple organisms include gastrointestinal or genitourinary fistulae, bladder outlet obstruction, neurogenic bladder, and indwelling catheters.
Traditionally, the standard definition for the presence of significant bacteriuria on urine culture has been greater than 105 cfu/mL. This may be an insensitive standard, as up to 50% of cases of acute cystitis have less than 105 cfu/mL. A urine culture demonstrating more than 102 cfu per mL may have the best combination of sensitivity (95%) and specificity (85%) for diagnosing acute cystitis in women. Practically, however, determination of colony counts by urine culture in this population is rarely necessary, except to confirm the diagnosis or differentiate from urethritis and vaginitis. In men with suspected UTI, a lower threshold is also used to define significant bacteriuria. Treatment and diagnosis are based on findings of more than 103-104 cfu/mL.5 It is prudent, as well, to consider a lower threshold for treatment in pregnancy. Asymptomatic bacteriuria during pregnancy is generally treated even when the count is less than 105 cfu/mL, especially when the organism is E. coli, Klebsiella pneumonia, Proteus mirabilis, Enterococcus, Pseudomonas, or group B Streptococcus or if the organism was identified on a catheterized specimen.23
Blood culture. Blood cultures are traditionally recommended for all cases of suspected pyelonephritis because of the high prevalence of bacteremia. Several studies, however, have suggested that blood cultures have limited usefulness in the management of adults with acute pyelonephritis, including pregnant patients. Blood cultures are positive 15-20% of the time, but results tend to parallel those of the urine cultures and rare, discrepant results do not alter the clinical management.37-39 Blood cultures may still be appropriate for the management of pyelonephritis in certain high-risk groups of patients. These include immunosuppressed patients; those in whom the diagnosis is not clear, including young children; patients in whom bacteremic seeding of the kidney is suspected, as in the setting of intravenous drug abuse or endocarditis; patients in whom a urine culture cannot be readily obtained and treatment may be delayed, as with bladder outlet obstruction; patients for whom history and physical examination are less reliable, as with young children and those with neurogenic disorders; and as part of a septic workup, as in infants younger than 60 days of age or the elderly.38-40
Imaging. Routine imaging studies for UTIs are rarely indicated as part of the ED evaluation. Evaluation of young women with acute or recurrent cystitis results in unnecessary costs and potential toxicity. Similarly, routine evaluation of acute and recurrent pyelonephritis in young women who respond promptly to antibiotics has a low diagnostic yield, as most have no functional or anatomic abnormality of the urinary tract. In women with two or more recurrences of pyelonephritis, suspected bacterial persistence, or complicating factors, imaging with CT or renal ultrasound may be indicated to rule out nephrolithiasis, obstructive uropathy, and perirenal or renal abscesses. Ultrasound is noninvasive, lacks radiation, and is more sensitive than excretory urogram in detecting focal masses and obstruction. Contrast-enhanced spiral computed tomogram may be the imaging modality of choice in adults for demonstrating anatomic and functional renal abnormalities associated with pyelonephritis. The value of urologic evaluation of men with a single uncomplicated UTI has not been determined, but it should probably only routinely be done in adolescents and men with pyelonephritis, recurrent infection, or whenever a complicating factor is present.5 Emergent imaging and consultation should be considered in patients who remain persistently febrile after 72 hours of treatment to rule out nephrolithiasis, obstructive uropathy, renal or perinephric abscesses, unrecognized urologic abnormalities, or other complications of pyelonephritis.
Modalities available for the evaluation of UTI include ultrasonography, computed tomography (CT), and Tc 99m-labeled dimercaptosuccinic acid (DMSA) renal scans in children. These modalities have largely replaced intravenous pyelography (IVP). Radionuclide imaging procedures have no role in the evaluation of adults with acute pyelonephritis; however, in children, DMSA renal scans may be useful in evaluating the acute febrile UTI where establishing the diagnosis of pyelonephritis may be difficult. Neonates, young infants, and children who are managed by clean intermittent catheterization, such as spina bifida patients, frequently present with nonspecific signs and symptoms. DMSA allows for accurate identification of acute pyelonephritis, the ability to document the extent and progression of renal parenchymal damage, and may be an important determinant of the need for antibiotic prophylaxis in some children.
Conventional recommendations for the universal investigation of UTI in children by ultrasonography, voiding cystourethrography, and DMSA scan (and sometimes IVP as well) are not based on any convincing evidence as to the necessity or effectiveness of such a routine. There now seems to be some reconsideration of when to evaluate children following UTI, and several less aggressive approaches have been advocated that recommend imaging only for specific indications such as acute pyelonephritis, first UTI in a boy, first UTI in a girl younger than 3 years of age, second UTI in girls 3 years of age or older, and first UTI in a child with a family history of UTI, genitourinary tract abnormalities, abnormal voiding patterns, hypertension, or poor growth. A recent, even less aggressive approach suggests that girls with afebrile UTI, presenting with lower urinary tract symptoms alone, need not undergo any imaging procedures.41-44 Nonetheless, because the timing and extent of evaluation of children with UTI is controversial, children with UTI should be referred to their pediatrician or primary care physician for consideration of imaging.
Plain film radiographs are of limited usefulness in the management of UTI. Plain abdominal films are not routinely ordered, but these films may be useful in the management of some children with suspected voiding dysfunction or constipation to assess bowel status, and, in some adults, as a rapid screening exam for detection of radiopaque calculi or unusual gas patterns seen in emphysematous pyelonephritis. A shielded chest x-ray to detect pneumonia or pleural effusion should be obtained in pregnant patients with pyelonephritis who present with signs of respiratory compromise, such as tachypnea or dyspnea. Fetal exposure to radiation is minimal with a shielded chest x-ray and no adverse sequelae have been associated with this study.
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