Etiology:
In very young children and infants the origin of UTI is most likely from hematogenous spread, whilst older children and in like adults the origin is from an ascending infection originating from the perineal area.
More frequent in females except for the first few months of life where it is more frequent in males, due to the fact malformations are more frequent in males and tend to present early. Obstruction to renal flow is a major risk factor, as urinary stasis provides the perfect environment for bacteria to grow. A short urethra is what predisposes girls to UTIs.
If a child is having recurrent UTI's suspect a urinary tract malformation.
E.coli causes 75%-90% of UTI episodes, other bacteria include klebsiella, proteus and enterococcus spp.
Presentation:
Varies with age of the patient. Neonates and infants are more likely to present with non specific symptoms such as; poor feeding, vomiting, failure to thrive, jaundice, hypothermia/fever, diarrhoea, strong smelling urine.
At around preschool age UTIs will present with more nephrogenic symptoms as well, such as dysuria, urgency and increased frequency.
Adolescents are more likely to have the classic adults symptoms. Important to note that adolescent girls are more likely to have vaginitis.
Diagnosis:
Diagnosis is classically difficult and based on urinalysis, urine culture, blood tests and imaging. bear in mind that urine test is not enough for diagnosis and culture is needed.
Urinalysis: typically leukocyte esterase and nitrites positive with presence of WBC sediment, the combination of these three has the highest sensitivity.
Urine culture: There are four ways in which urine can be sampled for culture in children.
-Suprapubic aspiration (sterile procedure, good for infants, obtains very good sample, bladder easily sampled with low complication rates)
-Bag collection (high chance of contamination thus, can be used to rule out infection is negative culture, but positive culture must be suspected to be a false positive), if you use a bag clean area well and bag must be changed every 20minutes to keep sterile, not recommended by CDC)
-Midstream collection (difficult in children, generally from only 3 years age in male children, make sure perineum area is cleaned well before hand)
-Catheter collection (performed as a sterile procedure, risks urethral trauma and introducing bacteria, used more for children with malformations in the urinary tract)
A clean catch urine sample with more than 100,000 CFUs (colony forming units) on culture of a single organism is classic criteria for UTI (>1000 CFUs for suprapubic aspiration). If there is growth of more than one organism consider that sample was contaminated.
Diagnosis in young children requires pyuria (>10 WBCs/mm3 in urine) and positive culture of a single pathogenic organism.
in older children and adults a single positive culture is enough.
Imaging:
Typically delayed by 3-6weeks unless urinary tract obstruction suspected or the child has an atypical UTI.
First line is Renal Ultrasound, it can spot many urinary tract abnormalities and is quick and cheap. However it poorly depicts the ureters and gives no functional information.
Micturating cystourethrogram (MCUG) shows anatomy well and can detect vescicoureteral reflux.
Nuclear cystography used when MCUG not possible and is great for serial follow up as radiation lower than in fluoroscopic studies.
Nuclear cortical scanning is best to see damage to kidney or presence of scarring. most frequently done with Tc11mDMSA. remember that it does not show the collecting system.
Treatment:
Initiate treatment immediately after culture drawn this reduces severity of damage to kidney (don't wait for culture results).
Antibiotics: 7-14 day course is standard (evidence that 2-4 days can be effective in lower urinary tract infections, if you can confirm no reflux). Oral treatment and parenteral treatment are equally efficacious as long as dosage correct. IV antibiotics recommended in children unable to tolerate oral therapy and infants less than one month until systemic infection ruled out.
In neonates: Ampicillin + Gentamicin/Cefotaxime
if you suspect an infected line or instrumentation cover for staph spp. with Vancomycin
Prevention:
Recurrent UTIs in 15% of children, quite often in children with malformations of the urinary tract (also without, 20% without any). Prophylactic antibiotic therapy is being debated and efficacy questioned.
Prophylaxis with Cotrimoxazole or Nitrofurantoin given at bedtime (to concentrate in bladder overnight). Nitrofurantoin is theoretically much better because it selects for the urinary tract however it commonly causes vomiting and hence is unpopular.
If recurrent UTI diagnosed then further imaging studies are recommended.
Last notes:
-An atypical UTI is one where the child is seriously ill or has one or more of the following:
poor urine flow, abdominal mass, raised serum creatinine, septicemia, infection with a non E.coli bacteria, failure to respond to treatment with suitable antibiotics within 48hours.
-The term UTI includes Cystitis, pyelonephritis and renal abscess (actually difficult to determine is upper or lower tract infection in children.
-Uncircumcised males have higher incidence if UTIs than circumcised males.
-Failure to thrive, feeding problems and fever are the most consistent symptoms
-Positive leukocyte esterase and nitrites dipstick test has sn 70% and sp 99%
-Bacteremia in 5% of cases of pyelonephritis.
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