As the foundations note set out, UTI means bacteria inside the urinary tract together with the body’s reaction to them. That is true at every age. What changes is the child who has it.
In an adult, the signs a doctor relies on are reports from the patient: where the pain is, what it feels like to pass urine, how sudden the urge is. A young child cannot give those reports, and a newborn shows few local signs at all. So the same infection looks like four different illnesses as childhood goes on. The reason is developmental rather than bacteriological.
Why can’t a young child tell you the usual symptoms?
The age band is read first, and the first reason the picture changes is that the signs naming a site are reports the child has to give. A child below roughly 3 years cannot localise pain. The same child cannot describe dysuria, and cannot report urgency. Without those reports the signs stay non-specific. Once the child can talk about bladder sensation, the textbook symptoms appear.
What do age and sex decide at the bedside?
With the reporting problem in mind, the clinician reads the age band first. It determines what to suspect, what to ask about, and how urgently to act. Sex and circumcision status then shift the picture within each band.
As the epidemiology note set out, the short urethra and the foreskin explain why girls and boys carry their risk differently. Girls carry the higher lifetime risk because the urethra is short, which shortens the distance the periurethral and vaginal flora must travel to reach the bladder. Boys’ risk is concentrated in infancy, in part because the foreskin provides a colonisable mucosal surface for uropathogens. The highest prevalence recorded in any group is in uncircumcised boys under 3 months with fever.
What does a newborn look like?
The youngest band is the one where the age band matters most, because the signs are systemic and non-specific. The neonate band is the first 28 days. The infection shows as the whole child being unwell rather than as a sign pointing to the urinary tract.
The features are:
- jaundice, including a conjugated hyperbilirubinaemia pattern
- fever or hypothermia
- poor feeding
- vomiting
- failure to thrive (poor weight gain)
The link with jaundice rests on an association: a case report describes a urinary tract infection that presented as cholestatic jaundice, so it is not a settled mechanism. Temperature is often the only objective abnormality in a neonate.
Why does a febrile newborn get urine and blood tests first?
A newborn’s illness is systemic, so the search is for sepsis rather than for a site. Urinary tract infection is a common cause of sepsis in infants. For that reason a neonate with fever and no clear focus needs blood and urine cultures, with empiric antibiotics started before the organism is known. This is needed rather than observation.
The same reasoning explains the speed. This age group can deteriorate quickly into urosepsis.
The urine is usually obtained by urethral catheter or suprapubic aspiration. Methods of collection differ in contamination and invasiveness. A bag or clean-catch sample can pick up bacteria from the skin and genital area, so a route that bypasses them is used in the young child. Waiting for a spontaneous void is not safe in an unwell neonate.
In this group the probability of UTI as the source of fever is highest in uncircumcised boys. The pooled prevalence in uncircumcised boys under 3 months is 20.1%.
What does an infant look like?
The infant is past the first 28 days, and the signs remain non-specific, so the reasoning changes from sepsis to excluding other foci first. The infant band is 1 month to about 18 months. The symptoms include fever, poor feeding, vomiting, diarrhoea and strong-smelling urine. None of them points to one organ, so the fever is not located at first. Irritability and crying do not localise either, for the same reason.
The reasoning is to exclude other bacterial foci first (otitis media, tonsillitis, pneumonia, meningitis) and then consider the urinary tract. An infant with fever and no focus has a pooled probability of UTI of 7.0% (95% CI 5.5–8.4). That figure justifies screening a urine specimen in this band rather than in every febrile child at every age. The earlier epidemiology note shows that the decision to test follows these probabilities.
What changes once a child can speak?
The preschool and school-age band is about 3 to 10 years. Once the child can describe pain and bladder sensation, the illness splits into two recognisable syndromes.
As the foundations note set out, febrile UTI is infection that has reached the kidney, and cystitis is infection confined to the bladder.
Pyelonephritis presents with abdominal or flank pain, sometimes with vomiting. The child can localise the painful side, so this presentation is usually taken seriously and investigated.
Cystitis presents with the lower-tract triad of dysuria, urgency and frequency. Cystitis is usually afebrile.
When does bed-wetting mean something?
A child who can describe bladder sensation may also show bed-wetting. In cystitis, secondary enuresis is an occasional soft sign rather than a diagnostic one.
The terms are easy to misuse. Enuresis is the clinical term; bed-wetting is the patient-facing equivalent. A child cannot be diagnosed with enuresis as a disorder before about 5 years. Night-time control is still developing before about 5 years, and it depends on bladder capacity and on waking to a full bladder. Nocturnal continence is usually achieved around age 5, roughly 2 years after daytime control.
Primary enuresis means never dry. Secondary enuresis means dry for a period, then wet again. This split becomes diagnostically meaningful from about age 5 onwards. Secondary enuresis raises the possibility of bladder inflammation, bladder-bowel dysfunction or UTI.
What changes in adolescence?
In the older child the same urinary symptoms can come from more than one source. Above roughly 10–12 years the symptom set is the adult pattern: dysuria, frequency, urgency, suprapubic discomfort, and sometimes visible haematuria. The list of other explanations changes at this age.
In adolescent girls presenting with dysuria, the differential is not confined to the urinary tract. Either a urinary infection or a sexually transmitted infection can cause the burning. Vaginitis and sexually transmitted infections are common explanations. In some series, urinary symptoms in adolescent females are more often associated with a sexually transmitted infection than with a UTI. A cystitis label without examining the external genitalia is therefore an incomplete assessment.
How does age guide a first decision?
With the four bands and the symptoms in place, a few typical children show how they combine. Age band plus presenting picture gives a first line of reasoning.
- A febrile 18-day-old with no focus: consider urosepsis first, because UTI is a common cause of sepsis in infants. The initial workup is catheter or suprapubic urine, blood culture and empiric antibiotics.
- A febrile 12-month-old, uncircumcised, with no focus: consider UTI, with a probability of about 7%. Take a urine specimen before antibiotics, by catheter if the child is unwell.
- A febrile 4-year-old girl with abdominal pain: consider pyelonephritis. Take a urine culture, treat empirically and image per local protocol.
- A 7-year-old with dysuria, frequency and secondary enuresis: consider cystitis. Take a clean-catch culture and treat empirically.
- A 15-year-old girl with dysuria: consider vaginitis or a sexually transmitted infection as well as UTI. The same symptom can come from either source, so the plan is external genital examination and testing, not antibiotics alone.
Why do age and symptoms not settle it?
The cases show how far age and presentation can go. Age bands and symptom patterns are clinical reasoning aids, not a quantitative risk score. The temperature thresholds and symptom combinations that shift pretest probability are not well defined in the literature. Neither age nor symptoms can settle the question. The diagnosis rests on the urine itself, and on how that urine was collected. If age and symptoms cannot settle it, what does, and how does the way the urine was collected change the answer?