Definition and Classification
A urinary tract infection (UTI) is an infection (most commonly bacterial, but, rarely, also viral and fungal) of any part of the urinary system, including the urethra, bladder, ureters, or kidneys.
- Pyelonephritis (upper UTI): infection involving the ureters and kidneys
- Cystitis (lower UTI): infection of the urinary bladder without renal involvement
- Asymptomatic bacteriuria: positive urine culture without symptoms
Epidemiology and Risk Factors
Prevalence of UTI:
- Age dependent: Infants (boys < 1; girls < 4) have a higher prevalence of UTI than older children.
- Gender dependent: Male:female ratio is 1:2 in the 1st year, increases to 1:10 beyond 1–2 years.
- Anatomy dependent: Prevalence is 8 times lower in circumcised boys than in uncircumcised boys.
- Ethnicity dependent: White children have a higher prevalence than Black children.
- Recent antibiotic therapy
- Sexual activity
- Bowel dysfunction (pediatric constipation)
- Indwelling catheter
- Urinary tract structural anomalies leading to obstruction
- Dysfunctional voiding (neurogenic bladder)
- Genetics (children with 1st-degree relatives with a history of pediatric UTI are more likely to have UTI)
Etiology and Pathophysiology
- Escherichia coli (75%–90%)
- Enterococcus faecalis
- Staphylococcus saprophyticus
- Group B streptococcus (neonates)
- Fungal (especially with instrumentation):
- Candida spp
- Asperigillus spp
- Cryptococcus neoformans
- Viral: adenovirus and other viruses (seen in cystitis with gross hematuria)
Normal urinary tract anatomy and/or urinary dynamics:
- Ascending infection
- Uropathogens (most commonly fecal flora) colonize periurethral area → ascend to bladder via urethra
- If pathogen reaches kidney via ureter → pyelonephritis or upper UTI
- Infection may occasionally enter blood → septicemia
- Hematogenous infection
- Septicemia → UTI
- Rarely seen, usually in immunocompromised patients
Abnormal urinary tract anatomy and/or urinary dynamics:
- Stagnation of urine leads to pathogen growth and UTIs
- Anatomical abnormalities leading to obstruction (ureteropelvic junction obstruction, posterior urethral valves)
- Neurological abnormalities leading to delay in emptying
- Vesicoureteral reflux (VUR): retrograde flow of urine from the bladder along the ureters
- Common and important cause of febrile UTI leading to pyelonephritis in children
- Has multiple etiologies
- Leads to renal scarring if not treated
Infants and young children
- Non-specific symptoms:
- Fever (may be the sole symptom, especially fever > 39℃ (101.2°F))
- Poor feeding
- Weight loss
- Changes in urinary habits:
- Holding urine due to painful urination
- New incontinence
Older (school-age and up) children
Presentation is similar to adults and clinical symptoms can be used to distinguish upper from lower UTI.
- Pain (abdominal, back, or flank)
- Nausea and vomiting
- Diarrhea (occasionally)
- Suprapubic pain and tenderness
- Malodorous urine
- Hematuria (caused by E. coli or adenovirus)
Workup and Diagnosis
Clinical suspicion based on age-appropriate symptomatology or urinalysis findings must be confirmed by urine culture.
Obtaining a urine sample
- Who to obtain a sample from:
- Children 0–2 months: all febrile infants
- Children 2–24 months: Decision is case dependent, based on height of fever and risk factors.
- Older children: only if symptoms are suggestive of UTI
- How to obtain a sample:
- Obtaining sterile urine is key to valid urinalysis results, but challenging with young children.
- Toilet-trained children: Attempt clean catch (take care to avoid contamination with skin flora).
- Children 2–24 months without toilet training:
- Place a bag over genital area (bag sample).
- Catheterization or suprapubic aspiration may be necessary.
- Urinalysis results may suggest UTI but are not diagnostic alone.
- Negative results in the presence of symptoms do not rule out UTI.
- Nitrites and leukocyte esterase usually positive with UTI
- Pyuria (leukocytes in urine):
- May be absent in UTI
- Sterile pyuria (positive leukocytes and negative culture) may be caused by:
- Prior antibiotic therapy
- Viral infections, tuberculosis, renal abscess
- Urinary tract obstruction
- Inflammation outside the urinary tract
- Interstitial nephritis
- Hematuria (increased RBCs) may be seen.
- Urinalyses suggestive of UTI must be confirmed by urine culture.
- Isolation of a single pathogen with one of the following criteria is diagnostic of UTI:
- Colony count > 10,000 in a symptomatic child
- Colony count > 50,000 from a suprapubic/catheter-obtained specimen
- Colony count > 100,000 from a urine bag
- Isolation of Lactobacillus spp., coagulase-negative staphylococci, and Corynebacterium spp. are not suggestive of UTI as these are normal skin flora.
When to perform:
- Very young children (< 2 months) who are at high risk for sepsis
- In suspected pyelonephritis before antibiotic therapy
Urinary tract infections in children may be indicative of underlying renal anatomical abnormalities, so some must be further investigated with imaging.
- Renal and bladder ultrasound (RBUS) should be performed:
- After 1st febrile UTI in all children 2–24 months
- In all children with recurrent cases of UTI
- After acute phase of illness; immediately with severe illness
- Voiding cystourethrogram (VCUG): Dye visible on X-ray is injected into the bladder and urine flow is visualized during voiding.
- Goal is to confirm presence of vesicoureteral reflux (VUR).
- Performed if:
- Ultrasound findings suggestive of high-grade (III and above) VUR (majority of grade I or II VURs resolve spontaneously)
- Evidence of obstruction, such as hydronephrosis or scarring
- Recurrent febrile UTI
- Late dimercaptosuccinic acid (DMSA) scan: no longer recommended by the American Academy of Pediatrics
Management and Follow-up
The main goal of treatment is prevention of renal complications, such as renal scarring, hypertension, and chronic kidney disease.
- Empiric antibiotic therapy:
- Early initiation (within 72 hours) prevents renal scarring.
- Should only be started after urine samples for testing have been collected
- Should only be started for patients with high likelihood of UTI:
- Fever > 39℃ (101.2)
- Known immune deficiency or renal anomaly
- Septic appearance
- Antibiotic choice:
- Should be tailored to bacterial species and sensitivity whenever possible
- Aimed at treating the most likely causative pathogen (E. coli)
- High kidney involvement risk → 2nd- or 3rd-generation cephalosporin
- Low kidney involvement risk → 1st-generation cephalosporin
- Admit to hospital if:
- Nauseous & vomiting
- < 1 month with suspected UTI
- < 2 months with febrile UTI
- Complicated infection (stones, obstruction, anomalies)
- 7–14 days of broad-spectrum antibiotics:
- Outpatient: oral 3rd-generation cephalosporins (cefixime)
- Inpatient: IV ceftriaxone, cefotaxime, or ampicillin with an aminoglycoside (gentamicin)
- Fluoroquinolones are effective antibiotics, but are best avoided in patients < 17 years of age.
- Urine culture: 1 week after completion of antibiotics to confirm treatment
- Renal abscess, perirenal abscess, or urinary tract obstruction: surgical or percutaneous drainage + antibiotics
- Children with history of only one uncomplicated UTI do not need follow-up.
- Nephrologist follow-up is recommended for children with:
- Recurrent UTI
- Severe VUR (grade III to V)
- Anatomical renal abnormalities
- Neurological disfunction of the bladder
- High blood pressure
- Antibiotic prophylaxis
- Still recommended for children with VUR grade III to V
- Millner, R., M.D., & Becknell, Brian,M.D., PhD. (2019). Urinary tract infections. Pediatric Clinics of North America, 66(1), 1-13. doi://dx.doi.org/10.1016/j.pcl.2018.08.002
- Jerardi, K. E., & Jackson, E. C. (2020). Urinary tract infections. In R. M. Kliegman MD, J. W. St Geme MD, N. J. Blum MD, Shah, Samir S., MD,MSCE, Tasker, Robert C., MBBS,MD & Wilson, Karen M., MD,MPH (Eds.), Nelson textbook of pediatrics (pp. 278-2795.e1) https://www.clinicalkey.es/#!/content/3-s2.0-B9780323529501005538
- Gupta, K., & Trautner, B. W. (2018). Urinary tract infections, pyelonephritis, and prostatitis. In J. L. Jameson et al. (Eds.), Harrison’s principles of internal medicine. New York, NY: McGraw-Hill Education. accessmedicine.mhmedical.com/content.aspx?aid=1159153646
- Robinson J. Antibiotic prophylaxis in vesicoureteral reflux: A practice revisited. Can Pharm J (Ott). 2013;146(2):84-87. doi:10.1177/1715163513481570