Contributors of Campbell-Walsh-Wein, 12th edition
Christopher S. Cooper, Douglas W. Storm, Antoine E. Khoury, and Elias Wehbi
Evaluation and management of a child with a fever
Up to 8% of febrile infections in infants and children are due to urinary tract infection (UTI). Even when another source of fever and infection such as otitis or respiratory infection has been identified, the reduction in risk of a concurrent UTI is only about 50%, so the clinician must consider the possibility of a UTI in any febrile infant. A summary of the evaluation and treatment of a child with a rectal temperature higher than 38°C is provided in Fig. 5.1 . A “toxic” appearing febrile child is much more likely to have a serious illness and some symptoms and signs of toxicity include irritability, lethargy, abnormal breathing, tachycardia, and cyanosis.
Definition of a urinary tract infection
What constitutes a “significant” clinical UTI in a child is controversial. The current diagnostic guideline in children 2–24 months from the American Academy of Pediatrics (AAP) requires a urinalysis (UA) with pyuria and/or bacteriuria and at least 50,000 CFU/mL of a uropathogen cultured from a urine specimen obtained through urethral catheterization or suprapubic aspiration. A small proportion of children with a significant UTI may not meet these criteria but do benefit from treatment.
Pathogenesis of UTI development
Most UTIs begin with periurethral contamination by a uropathogen from the gastrointestinal tract, which is most commonly Escherichia coli . These bacteria colonize the urethra, migrate to the bladder, invade the bladder cells, and may then ascend to the kidneys. Kidney colonization results in bacterial toxin production, host tissue damage, and possibly bacteremia ( Fig. 5.2 ).
Risk factors leading to pediatric urinary tract infections
Gender and age.
The only time that UTIs are more prevalent in boys than in girls is at an age younger than 1 year. About 2% of boys and 0.7% of girls experience a UTI during the first year of life; however, 7% of girls and 2% of boys experience a UTI by 6 years of age.
Circumcision.
Circumcision reduces UTI development in the first 6 months of life by almost 10-fold.
Anatomic abnormalities.
Anatomic abnormalities predisposing to UTIs include hydronephrosis and hydroureteronephrosis from ureteropelvic junction obstruction (UPJO) or ureterovesical junction obstruction (UVJO), vesicoureteral reflux (VUR), infection stones, infected nonfunctional renal segments or papillae, and urethral obstruction. With the exception of VUR, these abnormalities are often evident on a renal and bladder ultrasound (RBUS), which is currently recommended in young children after their first febrile UTI.
Vesicoureteral reflux (VUR).
VUR occurs in 1%–2% of all newborns, but it is found in 25%–40% of children after their first episode of UTI. The incidence of VUR decreases with increasing age ( Table 5.1 ) VUR facilitates ascent of bacteria from the bladder to the kidney; however, approximately 50%–70% of children with pyelonephritis will not have VUR.
| GRADE | DESCRIPTION |
|---|---|
| 1 | Into a nondilated ureter |
| 2 | Into the pelvis and calyces without dilation |
| 3 | Mild to moderate dilation of the ureter, renal pelvis, and calyces with minimal blunting of the fornices |
| 4 | Moderate ureteral tortuosity and dilation of the pelvis and calyces |
| 5 | Gross dilation of the ureter, pelvis, and calyces; loss of papillary impressions; and ureteral tortuosity |
Sexual activity.
Sexual activity increases the risk of UTI.
Bladder and bowel dysfunction (BBD).
BBD predisposes to UTI, and treatment of BBD reduces recurrent UTIs as well as incontinence and VUR.
Iatrogenic factors.
Catheter-associated UTI (CAUTI) is the most common nosocomial infection, and the risk of UTI increases with the duration of the catheter. Removal of urethral catheters in hospitalized patients is recommended as soon as possible.
Biofilms
Biofilms are communities of microorganisms encapsulated with a self-developed polymeric matrix and adherent to either a living or inert surface. Antibiotics are often unable to eradicate bacteria within a biofilm leading to bacterial persistence.
Classification of pediatric urinary tract infections
Cystitis and pyelonephritis
UTIs are classified as cystitis or pyelonephritis based on their symptoms despite a high false-positive rate with this approach. Cystitis is suspected when the child is afebrile and has only lower urinary tract symptoms including urinary urgency, frequency or dysuria, malodorous urine, and/or suprapubic tenderness. Children with a UTI are assumed to have pyelonephritis when they have high fevers, nausea, vomiting, flank pain, or lethargy. Of note, in patients with fever and systemic symptoms, only 50%–66% demonstrated acute inflammatory changes in the kidney on 99m Tc-dimercaptosuccinic acid (DMSA) scans.
Asymptomatic bacteriuria (ASB)
ASB occurs in 0.8% of preschool girls and is defined as the presence of two consecutive urine specimens yielding positive cultures (>10 5 CFU/mL) of the same uropathogen. In school-age girls, spontaneous resolution of ASB occurs in 50%. Children with ASB do not require antibiotics because they do not appear to be at any risk for recurrent symptomatic infections, renal damage, or impaired renal growth. An important exception is that infants with ASB are at risk for developing significant UTIs, and they should be treated with antimicrobial therapy and imaged to evaluate for any congenital abnormalities.
Bacterial nephritis
Acute bacterial nephritis occurs as the inflammation from bacterial infection spreads throughout the kidney. A localized form of this inflammation is called acute focal bacterial nephritis or lobar nephronia . Computed tomography (CT) findings include global renal enlargement and inflammatory changes in the perirenal fat and Gerota fascia. CT with contrast images demonstrate ill-defined, nonhomogeneous areas of decreased parenchymal enhancement that typically are wedge shaped ( Fig. 5.3 ).
Pyonephrosis
Pyonephrosis consists of purulent exudate accumulating in the renal collecting system and is frequently associated with obstructed urinary outflow from the renal pelvis.
Acute renal abscess
Symptoms of a renal abscess are similar to pyelonephritis; however, in up to 20% of renal abscess cases, the urine culture result may be negative, which increases the chance that the etiology was via hematogenous seeding of the kidney. CT imaging findings may include (1) a well-defined area of low attenuation or decreased enhancement or (2) a striated, wedge-shaped zone of increased or decreased enhancement.
Diagnosing a pediatric urinary tract infection
Symptoms
The diagnosis of a UTI may be difficult because the symptoms can be nonspecific and require a high degree of suspicion, especially in very young children. Symptoms may include fever, irritability, poor feeding, jaundice, failure to thrive, vomiting, diarrhea, abdominal distention, or foul-smelling urine. In children younger than 2 years of age, the presence of a fever higher than 40°C, history of a previous UTI, suprapubic tenderness, or an uncircumcised penis are the most useful symptoms and signs in predicting a UTI. Older children often present with classic UTI symptoms, including abdominal pain, back pain, dysuria, urinary frequency, and incontinence. The possibility of sexually transmitted diseases in older children and adolescents with symptoms of urethritis must be considered and may be caused by Neisseria gonorrhoeae , Chlamydia trachomatis , or Ureaplasma urealyticum .
Physical examination
Specific findings on physical examination in young children are rare and may consist of fever or lethargy. An enlarged obstructed bladder or kidney may be palpable as an abdominal or flank mass, respectively. Older children may experience suprapubic, abdominal, or flank tenderness. Costovertebral angle tenderness suggests pyelonephritis. Examination of the external genitalia should be performed to evaluate for signs of trauma, local inflammation, urethral meatal stenosis or discharge, phimosis, foreign body, and anatomic abnormalities in girls such as an ectopic ureteral orifice or urethral mass from a prolapsing ureterocele. Testicular examination may demonstrate tenderness from epididymo-orchitis. Examination of the back for signs of spina bifida occulta such as a prominent fat pad or asymmetric gluteal cleft or sacral dimple, along with a neurologic examination, may point to underlying neurologic causes predisposing to UTIs.
Urine collection methods.
The chance of collecting a contaminated urine specimen increases with the decreasing degree of invasive collecting methods. The urine from a collection bag only provides reliable information when the specimen is normal and thereby rules out a UTI. A clean-catch midstream urine sample carries a higher chance of contamination than urine collected via more invasive methods, including catheterization or suprapubic aspiration (SPA). The clean-catch urine is more reliable in an older girl or a circumcised boy. For nontoilet-trained febrile children younger than 2 years of age, the AAP guidelines recommend SPA or catheterization.
Successful catheterization in girls often requires a two-person technique. The labia majora should each be placed on gentle traction outward from the body and slightly lateral to expose the vaginal and urethral openings and facilitate the correct location for catheter insertion. This method, as opposed to using a single hand and fingers spreading the labia laterally, more routinely exposes the normally recessed urethral opening and surrounding anatomic landmarks.
Urine dipstick tests.
Leukocyte esterase is released from white cells broken down in the urine and serves as a marker for pyuria. False positives result from other causes of inflammation. Urinary nitrite is reduced from nitrates by gram-negative enteric bacteria and requires several hours to occur; thus, a first-morning urine has the best sensitivity with this dipstick test. Frequent urination may not permit enough time for the conversion of nitrates to nitrites and results in a false-negative nitrite test. A dilute urine may also generate a false-negative test or infection with gram-positive organisms that do not reduce nitrates.
The sensitivity of leukocyte esterase for detecting UTI is estimated at 80% with specificity ranging from 64%–92%. The sensitivity of the nitrite test is 50%; however, the specificity is very high at 98%, meaning a positive nitrite test likely reflects a true UTI.
Urine culture.
A positive urine culture is essential for the diagnosis of a UTI; however, the definition of what constitutes a true positive culture based on the number of colony-forming units (CFU) per milliliter of urine is variable between guidelines. The AAP guidelines require 50,000 CFU/mL along with a positive UA for pyuria in a catheterized specimen.
Radiographic imaging
Controversies with imaging strategies.
Despite prevalence rates of VUR of up to 40%, the revised AAP guidelines recommended routinely obtaining a renal ultrasound in all children less than 2 years of age with a febrile UTI but not a voiding cystourethrogram (VCUG) if the ultrasound is normal. The Section of Urology of the AAP recommends that a VCUG remain an accepted option following a first febrile UTI. Most agree with obtaining a VCUG in children with recurrent febrile UTIs or if an RBUS demonstrates structural renal anomalies, asymmetry in renal size, ureteral dilation, or bladder anomalies.
Ultrasound.
1%–2% of children with a history of UTI exhibit an abnormality on RBUS requiring additional evaluation. The RBUS is used to follow renal growth in children with a history of UTIs or VUR with kidney size referenced to standard renal growth curves. Of note, the RBUS has a very low sensitivity for the detection of VUR, even in children with high grades of VUR.
Voiding cystourethrogram.
When performed with contrast, the VCUG remains the gold standard imaging technique for the detection and grading of VUR. Because of the improved anatomic resolution, many prefer to use a contrast VCUG as the initial method of evaluation and reserve a radionuclide cystogram (RNC) for follow-up imaging ( Fig. 5.4 ). Recently, in order to eliminate radiation exposure, there is increasing interest and use of contrast-enhanced voiding urosonography in place of VCUG or RNC. In general, the timing of obtaining a VCUG is delayed at least 1 week after treating a UTI to allow for recovery from the infection but may be performed earlier once the urine is sterile and the child has clinically improved. Techniques employed to decrease the child’s anxiety and discomfort associated with a VCUG include the use of topical urethral anesthetic, child-life distraction, sedation, and hypnosis.
Related posts:
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Urologic evaluation of the child
Evaluation of the urologic patient: History, physical examination, laboratory tests, imaging, and hematuria workup
Congenital anomalies of the upper urinary tract: UPJ obstruction, duplication anomalies, ectopic ureter, ureterocele, and ureteral anomalies
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