Urinary Tract Infection (UTI) Overview

Urinary Tract Infection (UTI) Prevalence

• UTIs occur in 1-3% of girls and 1% of boys.
• In girls, the first UTI typically occurs by age 5, peaking during infancy and toilet training.
• In boys, most UTIs occur during the first year of life.
• UTIs are significantly more common in uncircumcised boys, particularly during the first year.
• The male-to-female ratio for UTIs during the first year is 2.8-5.4:1.
• After 1-2 years, females are more prone to UTIs, with a 1:10 ratio.

UTI Etiology

• Colonic bacteria cause 75-90% of UTIs in girls.
• Escherichia coli is the most common culprit, followed by Klebsiella spp. and Proteus spp.
• In boys over 1 year old, Proteus spp is as common as E. coli.
• Other pathogens include gram-positive organisms like Staph saprophyticus, enterococcus and adenovirus (cystitis).
• These pathogens affect both sexes.

UTI Clinical Manifestations

• Pyelonephritis
• Cystitis
• Asymptomatic bacteriuria (ABU)
• Focal nephronia
• Renal and perirenal abscess

Clinical Pyelonephritis

• Symptoms may include abdominal/flank pain.
• Often accompanied by fever and malaise.
• Nausea, vomiting, and diarrhea are possible.
• Infants may show nonspecific symptoms like poor feeding, jaundice, irritability and weight loss.
• Fever without a focus of infection is common in infants under 24 months, with pyelonephritis being the most common serious bacterial infection.
• Acute pyelonephritis can lead to renal injury and scarring.

Cystitis

• Symptoms suggest bladder involvement.
• Include dysuria, incontinence, malodorous urine, urgency, frequency and suprapubic pain.
• Cystitis does not cause fever or renal injury.
• Malodorous urine is not specific for a UTI.

Asymptomatic Bacteriuria (ABU)

• A positive urine culture without any visible signs or symptoms of infection.
• More prevalent in girls, especially in pre-school or school-aged children (1-2% in girls and 0.03% in boys).
• Incidence decreases with age.
• Benign condition, and not associated with renal injury.

UTI Pathogenesis and Pathology

• UTIs are ascending infections; bacteria originate from fecal flora, colonize the perineum, and ascend to the bladder through the urethra.
• In uncircumcised boys, bacteria originating from beneath the foreskin (prepuce) are a common source.
• Vesico-ureteral reflux (VUR) is a common cause of UTIs, particularly in children with congenital or acquired reflux.
• Urine can backflow from the bladder to the kidney in VUR; this introduces bacterial pathogens to the kidney, potentially leading to pyelonephritis.
• Kidney infections can rarely develop from blood-borne bacteria.
• Certain papillary structures in the kidneys allow urine to flow into the collecting tubes; if infected, this can result in an inflammatory/immunologic response that leads to damage and scarring of the kidneys.

UTI Diagnosis

• Suspicion of UTI based on symptoms or urinalysis results.
• Urine culture is essential for confirming a UTI.
• For toilet-trained children, a mid-stream urine sample is collected.
• Urine sample culture should show >100,000 colonies of a single pathogen or >10,000 colonies and symptoms for UTI diagnosis.
• Uncircumcised males require prepuce retraction.
• Infants require sterile collection bags after skin disinfection.
• Positive urinalysis results coupled with symptoms and >100,000 colonies in culture suggest a UTI.
• If criteria aren't met, cultures from suprapubic or catheterized samples may be used to confirm or rule out a UTI.

UTI Urinalysis

• Pyuria (leukocytes in urine) indicates possible infection.
• An absence of pyuria doesn't exclude the presence of urine infection.
• White blood cells in the urine (hematuria) or casts often accompany acute cystitis.
• White blood cell casts in the urinary sediment suggest kidney involvement.
• If a child with symptoms has negative urinalysis, a UTI could still be present.
• Lab tests like leukocytosis, neutrophilia, increased ESR, and C-reactive protein (nonspecific inflammatory markers) are possible findings in acute kidney infection (pyelonephritis), elevated to 20-25,000/mm³ in cases of renal abscess.
• Blood cultures are often done to rule out sepsis in pyelonephritis, particularly in infants or children with urinary tract abnormalities.

Imaging Studies

• Renal sonogram is common for clinical pyelonephritis (febrile UTI) to assess kidney size, rule out renal scarring, hydronephrosis, and structural problems.
• Large disparity in kidney size may signify growth impairment.
• DMSA scans assess parenchymal involvement; used to evaluate for kidney scarring in febrile UTIs.
• Vesicoureteral reflux (VUR) is assessed using a voiding cystourethrogram (VCUG) in cases of recurrent febrile UTIs or atypical symptoms, such as failure to respond to antibiotics, abnormal ultrasound results (hydronephrosis, enlarged bladder wall thickness), severe lower UTI symptoms with multiple episodes.

Host Risk Factors

• Vesicoureteral reflux (VUR).
• Obstructive uropathy leading to urinary stasis.
• Urethral instrumentation during procedures.
• Toilet training difficulties or refusal to use the bathroom.
• Voiding dysfunction, especially in young girls.
• Neurogenic bladder.

UTI Complications

• Pyelonephritis: an acute kidney infection.
• Renal scarring and/or damage.
• Chronic kidney disease/insufficiency
• Sepsis (blood poisoning).

UTI Treatment

• Acute cystitis and pyelonephritis should be treated promptly.
• Mild or uncertain cases might delay confirmation with a urine culture.
• Initial treatment often includes antibiotics, such as trimethoprim-sulfamethoxazole or nitrofurantoin.
• If the infection is severe or in infants or small children, IV antibiotics are necessary. Also important to observe for worsening symptoms, or if symptoms worsen, immediate evaluation of severe infection in children.
• Alternative or additional options include broad-spectrum antibiotics (oral 3rd generation cephalosporins).
• A urine culture performed 1-2 weeks following treatment ensures sterility.

UTI Treatment for Children Requiring Hospitalization

• Dehydration, vomiting or inability to drink fluids, less than 1 month of age, or if sepis is suspected, hospitalization is indicated.
• Intravenous fluids and antibiotics.