eMedicine Specialties > Pediatrics: General Medicine > Infectious Disease

Urinary Tract Infection

Author: Stanley Hellerstein, MD, Pediatric Nephrologist, Children's Mercy Hospital of Kansas City; Ernest L Glasscock, MD Chair in Pediatric Research, Professor of Pediatrics, University of Missouri School of Medicine at Kansas City
Contributor Information and Disclosures

Updated: Nov 23, 2009

Introduction

Background

Urinary tract infection (UTI) is one of the most common infections of childhood. It distresses the child, concerns the parents, and may cause permanent kidney damage.

In some instances, urinary tract infection results in recognition of an important underlying structural or neurogenic abnormality of the urinary tract. The febrile infant or child with clinically significant bacteriuria and no other site of infection to explain the fever, even in the absence of systemic symptoms, has pyelonephritis (ie, upper urinary tract infection). The graph below details a reasonable approach for febrile infants younger than 3 months with a temperature of more than 38 º C.

The site of infection is often unclear when a child with pyuria and clinically significant bacteriuria has another potential source of fever (eg, otitis media, pharyngitis). When urinary tract infection is diagnosed in a child, an attempt should be made to identify any risk factors for the urinary tract infection (eg, anatomic anomaly, voiding dysfunction, constipation).

Pathophysiology

Almost all urinary tract infections are ascending in origin. Disturbance of the normal periurethral flora, which is part of the host defense against colonization by pathogenic bacteria, predisposes a person to a urinary tract infection. Bacteria of the periurethral flora also inhabit the distal urethra. Urine in the proximal urethra, urinary bladder, and other proximal sites in the urinary tract is normally sterile. Uropathogens must gain access to the urinary bladder and proliferate for infection to occur. Uropathogens in the distal urethra may gain access to the bladder because of turbulent urine flow during normal voiding or because of dysfunctional voiding. Successful urinary bladder colonization is unlikely unless bladder defense mechanisms are impaired because normal voiding usually results in an essentially complete washout of contaminating bacteria.

After birth, the periurethral area, including the distal urethra, becomes colonized with aerobic and anaerobic microorganisms that appear to function as a defense barrier against colonization by uropathogens. In early childhood, enterobacteria and enterococci are part of the normal periurethral flora. Escherichia coli is the dominant gram-negative species in young girls, whereas E coli and Proteus species predominate in boys. Children as old as about 5 years are predisposed to have urinary tract infections, partly because of periurethral colonization by E coli, enterococci, and Proteus species. These potential uropathogens usually diminish in the first year of life and are rarely found in children older than 5 years. Studies of girls and women prone to urinary tract infection showed that periurethral colonization occurs with the specific bacterium that causes the next infection.

Frequency

International

Studies from Sweden have indicated that at least 3% of girls and 1% of boys have a symptomatic urinary tract infection by the age of 11 years. However, data from recent epidemiologic surveys suggest incidences higher than these. Occurrences of a first-time symptomatic urinary tract infection are highest for both boys and girls during the first year of life and markedly decrease after that. The minimum cumulative incidence in both boys and girls aged 2 years is slightly over 2%. Most episodes of urinary tract infection during the first year of life are pyelonephritis. After 2 years of age first-time urinary tract infection manifesting as cystitis is common among girls. More recent data suggest that 8% of girls have a symptomatic urinary tract infection during childhood. The incidence of a first urinary tract infection in boys older than 2 years is exceedingly low, probably less than 0.5%.

Mortality/Morbidity

Mortality related to urinary tract infection is exceedingly rare for otherwise healthy children in developed countries.

Morbidity associated with pyelonephritis is characterized by systemic symptoms, such as fever, abdominal pain, vomiting, and dehydration. Bacteremia and clinical sepsis may occur. Children with pyelonephritis also may have cystitis. Long-term complications of pyelonephritis are hypertension, impaired kidney function, end-stage renal disease (ESRD), and complications of pregnancy (eg, urinary tract infection, pregnancy-related hypertension, low-birth-weight neonates).

The voiding symptoms of cystitis are usually transient, clearing within 24-48 hours of effective treatment. Long-term complications of urinary tract infection are caused by renal damage secondary to pyelonephritis. Cystitis may cause voiding symptoms and require antibiotics, but it is not associated with long-term deleterious kidney damage.

Race

Data are scant. However, in studies by Hoberman et al, the prevalence of a febrile urinary tract infection in white infants exceeded that of black infants.¹ These investigators found that 17% of white female infants younger than 1 year with a temperature of 39°C or more seen in an emergency department had urinary tract infections.

Sex

During the first few months of life, the incidence of urinary tract infection in boys exceeds that in girls. By the end of the first year and thereafter, both first-time and recurrent urinary tract infections are most common in girls. The prevalence of urinary tract infection in girls aged between 1 and 2 years is 8.1%; in boys, it is 1.9%. The rate in circumcised boys is low, 0.2-0.4%. The rate in uncircumcised boys is 5-20 times higher than in circumcised boys.

In a systematic review, investigators calculated crude estimates of urinary tract infection during the first 24 months of life.² Rates were 3% in boys younger than 1 year, 2% in boys older than 1 year, 7% in girls younger than 1 year, and 8% in girls aged 1-2 years.

Age

First-time urinary tract infection is most common in the first 2 years of life.

Clinical

History

The 2 broad clinical categories of urinary tract infection (UTI) are pyelonephritis, or upper urinary tract infection, and cystitis, or lower urinary tract infection. The history and clinical course varies with the patient's age and the specific diagnosis.

• Children aged 0-2 months: Neonates and infants in this age range who have pyelonephritis usually do not have symptoms localized to the urinary tract. Urinary tract infection is discovered as part of an evaluation for neonatal sepsis.
• Infants and children aged 2 months to 2 years
  • Infants and young children in this age range with pyelonephritis may have a history of unexplained fever (eg, rectal or tympanic membrane–derived temperature of >38°C).
  • These patients are at higher risk for renal injury than are older children, possibly because the lack of localizing signs of infection delays the start of antibiotic therapy. This situation had led to a 3-day rule: An infant or child with unexplained fever should not be observed for more than 3 days without a urine specimen being obtained.
  • Some infants with pyelonephritis in this age range have fever and few other symptoms, whereas others are acutely ill and have a history of irritability, decreased oral intake, abdominal pain, vomiting, and loose bowel movements.
  • Children aged 1-2 years may present with voiding symptoms suggestive of cystitis, with crying on urination or only a foul odor to the urine in the absence of clinically significant fever (temperature <38°C).
• Children aged 2-6 years
  • Children in this age group with febrile urinary tract infection (pyelonephritis) usually have systemic symptoms with loss of appetite; irritability; and abdominal, flank, or back pain. Voiding symptoms may be present or absent.
  • Children with acute cystitis have voiding symptoms with little or no temperature elevation. Voiding dysfunction may include urgency, frequency, hesitancy, dysuria, or urinary incontinence.
  • Suprapubic or abdominal pain may be present, and the urine sometimes has a strong or foul odor.
• Children older than 6 years and adolescents
  • Urinary tract infection among children in this age range usually affects the lower tract, but pyelonephritis also occurs. Symptoms are similar to those in children aged 2-6 years.
  • Girls who have pyelonephritis in infancy or early childhood, including those with persistence of vesicoureteric reflux (VUR), usually have cystitis with urinary tract infection when they are older. They are also prone to have a recurrence during pregnancy.

Physical

• Findings on physical examination, such as tenderness in the costovertebral angle or flank, may help localize the site of infection to the kidney. Suprapubic tenderness may be present.
• Infants and younger children with pyelonephritis usually have no localizing findings, but they are febrile and irritable.
• The older children with pyelonephritis often have tenderness of the flank or costovertebral angle, and those with cystitis may have suprapubic tenderness.

Causes

Proliferation of bacteria in the urinary tract is the cause of urinary tract infection.

• Infections are almost always ascending in origin and caused by bacteria in the periurethral flora and the distal urethra. These bacteria inhabit the distal GI tract and colonize the perineal area. E coli usually causes a child's first infection, but other gram-negative bacilli and enterococci may also cause infection.
• Staphylococcal infections, especially those due to Staphylococcus saprophyticus, are common causes of urinary tract infection among female adolescents.
• Entry of bacteria into the urinary bladder may be the result of turbulent flow during normal voiding, voiding dysfunction, or catheterization. In addition, sexual intercourse or genital manipulation may foster the entry of bacteria into the urinary bladder. More rarely, the urinary tract may be colonized during systemic bacteremia (sepsis); this usually happens in infancy.
• Risk factors for urinary tract infection include the following:
  • Children who receive broad-spectrum antibiotics (eg, amoxicillin, cephalexin) that are likely to alter GI and periurethral flora are at increased risk for urinary tract infection because these drugs disturb the natural defense against colonization by pathogenic bacteria.
  • Prolonged incubation of bacteria in bladder urine due to incomplete bladder emptying or infrequent voiding compromises an important bladder defense against infection. Symptoms of voiding dysfunction, such as urgency, frequency, hesitancy, dribbling, or incontinence may occur in the absence of infection or local irritation because of uninhibited detrusor contractions. When the child attempts to prevent incontinence during a detrusor contraction by posturing (eg, obstructing the urethra), bacteria-laden urine in the distal urethra may be milked back into the urinary bladder (urethrovesical reflux). This mode of bacterial access is a common risk factor for urinary tract infection among pediatric patients who use posturing or pelvic withholding procedures to prevent incontinence.
  • Voiding dysfunction is not usually encountered in a child without neurogenic or anatomic abnormality of the bladder until the child is in the process of achieving daytime urinary control. Children with voiding dysfunction may attempt to prevent incontinence during an uninhibited detrusor contraction by voluntarily increasing outlet resistance. This may be achieved by using various posturing maneuvers, such as tightening of the pelvic-floor muscles, applying direct pressure to the urethra with the hands, or performing the Vincent curtsy, which consists squatting on the floor and pressing the heel of one foot against the urethra.
  • Constipation, with the rectum chronically dilated by feces, is an important cause of voiding dysfunction. Neurogenic or anatomic abnormalities of the urinary bladder may also cause voiding dysfunction.
  • Neonatal circumcision decreases the risk of urinary tract infection by about 90% in male infants during the first year of life. The risk of urinary tract infection in a circumcised infant is about 1 in 1000 during the first year, whereas an uncircumcised male infant has a 1 in 100 risk of developing a urinary tract infection. Given this risk, 111 healthy male infants must be circumcised to prevent 1 urinary tract infection. The risk and long-term effect of scarring due to 1 preventable urinary tract infection in a male infant are not known.

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