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What you need to know about childhood UTIs

Paediatric nephrologist Dr Rodney Gilbert answers GP Dr Sabby Kant’s questions on the usefulness of urine dipsticks, antibiotic choice and how age affects management

Paediatric nephrologist Dr Rodney Gilbert answers GP Dr Sabby Kant's questions on the usefulness of urine dipsticks, antibiotic choice and how age affects management

1 What underlying factors and pathology contribute to UTIs in children?

For reasons that aren't clear, boys are at higher risk of infection in infancy. Some 75% of UTIs in the first year are in boys. In school-age children, girls account for almost all UTIs, probably because of the shorter female urethra. Uncircumcised boys are at significantly higher risk than those who are circumcised.

The most important defence is regular and complete emptying of the bladder. Anything that interferes with this creates a stagnant pool of urine in which bacteria can multiply, making infection more likely.

For example, high-grade vesico-ureteric reflux results in a significant portion of the urine in the bladder travelling back towards the kidney rather than being expelled, resulting in incomplete emptying1.

Other causes of retention include obstruction – such as posterior urethral valves, vesico-ureteric junction obstruction – and neuropathic bladder. An important and common cause is chronic constipation.

Another risk factor is the presence of foreign material in the urinary tract, most commonly stones.

Sexual activity in both adolescent and adult females is a common cause of UTI and sexual abuse needs to be considered in girls with recurrent UTI.

UTIs are common – at least 10% of girls will have at least one infection – but most children who get a UTI have a normal tract.

2 Can you describe the presenting clinical features of UTI in children of various ages?

In neonates, signs of sepsis – fever, irritability or hypothermia – are present in up to half of affected children. Jaundice is present in perhaps one-third. Poor feeding and lack of weight gain may be present. Infection is asymptomatic in 10% or more.

In the under-fives, a history of fever is present in 60-80% of children. Other symptoms are dysuria, irritability, malaise, abdominal pain and anorexia. Macroscopic haematuria should always alert you to the possibility of UTI. But proteinuria, especially if isolated, is not a feature of UTI.

In children over five, the features of UTI are the same as in adults, namely frequency and dysuria in cystitis with the addition of fever – possibly with rigors – and loin pain in pyelonephritis.

3 Which bacteria are the most common culprits and how should this influence treatment?

E. coli is responsible for about 80% of UTIs. About 15% are caused by other gram-negative organisms such as klebsiella, enterobacter, proteus and pseudomonas.

Fewer than 5% of UTIs are caused by gram-positive organisms, most frequently enterococcus. Staphylococcus is usually a contaminant but can, on rare occasions, cause genuine infection.

If organisms other than E. coli are isolated this should raise suspicion of underlying significant structural abnormalities. This is particularly true of Pseudomonas sp., which almost never causes infection in a structurally normal tract.

Assume the infection is almost certainly caused by a gram-negative organism – most probably E. coli – when choosing an antibiotic. There is increasing resistance to trimethoprim and amoxicillin. For patients well enough to receive oral antibiotics, a cephalosporin or co-amoxiclav are reasonable choices.

4 How does a urine dipstick help management?

The important tests as far as the diagnosis of UTI is concerned are leukocyte esterase (white blood cells) and nitrites. The sensitivity of dipsticks for detecting UTI is high, but the specificity is low. If both leukocyte esterase and nitrites are negative, this excludes UTI with about 95% certainty at all ages. For children over two years of age the negative predictive value approaches 100%. If both are positive, the positive predictive value is about 66%.

It's extremely important that a freshly voided sample is tested, as contaminating organisms can metabolise urinary nitrate to nitrite in a sample kept at room temperature for a few hours.

Dipsticks give an immediate result, unlike culture. Microscopy can give an immediate result but is obviously not practical in primary care. Dipsticks can therefore be used to exclude UTI as an explanation for symptoms such as fever or allow a presumptive diagnosis of UTI, allowing immediate antibiotic therapy.

5 Once a UTI is confirmed, which investigations are required and which can and should GPs initiate?

The recent NICE guidelines2 recommend far fewer investigations than the 1991 Royal College of Physician guidelines. The investigations recommended depend on the child's age and clinical presentation and are given in the table overleaf.

If an infant responds well to antibiotics and has no ‘atypical' features, only an interval ultrasound scan is routinely required. Infants under three months should all be referred for specialist care but in those aged three to six months it would be perfectly appropriate for the GP to request the scan. If it is normal, no further imaging is required. If abnormal, further investigation and possibly specialist referral may be indicated.

Atypical features include:

• serious illness including septicaemia

• a history of poor urine flow

• a palpable abdominal mass

• raised plasma creatinine concentration

• failure to respond within 48 hours of antibiotic therapy.

Infections caused by organisms other than E. coli are also considered atypical. These children need additional investigation and should be referred.

Recurrent UTI is defined as two or more episodes of UTI with features of pyelonephritis in at least one episode, or three episodes without features of pyelonephritis.

Children aged six months or older who have an uncomplicated episode of UTI that responds to antibiotics within 48 hours need no imaging. For those with atypical features or recurrent UTI, the recommended imaging investigations are shown in the table.

Further investigation may be required if abnormalities are detected on ultrasound or dimercaptosuccinic acid (DMSA) scan. Children with atypical infections should in most cases be referred. In those with recurrent UTI it would be appropriate for the GP to request the investigations.

6 At what age is investigation after a single or recurrent UTI no longer required?

This depends on the clinical course of the infection. All children under six months of age should have at least an ultrasound scan, with a DMSA scan and a micturating cystourethrogram (MCUG) added in certain cases. Children over six months of age need no investigation provided they do not have atypical features and respond well to therapy within 48 hours.

The atypical features that indicate the need for imaging investigations are severe illness, palpable kidneys or bladder, history of poor urinary stream, bacteraemia, renal impairment or growth of organisms other than E. coli.

7 Once UTI is confirmed, investigated and treated, what do we need to do in terms of long-term monitoring?

Children with significant urinary tract abnormalities, including dysplasia or abnormal renal function, should be referred. Patients with severe scarring on DMSA scan should also see a specialist but those with less severe scarring can certainly be managed in general practice. The most important potential complication is hypertension, but the risk is small.

My practice is to recommend an annual blood pressure check and a check for proteinuria for these patients. It is important that BP is compared with the normal range for age and height3. In my experience, most GPs are happy to undertake this surveillance once the child is big enough to use a standard adult cuff when measuring BP.

Routine use of prophylactic antibiotics is not recommended after a single infection. A recent Cochrane review failed to show a benefit from prophylaxis even in patients with vesico-ureteric reflux and concluded that there was no treatment that was superior to vigilance for UTI and early treatment for any UTIs that do occur4. If a child is on prophylaxis and develops a UTI, they should be given a different antibiotic, not a bigger dose of the same antibiotic.

8 What are the short- and long-term consequences of untreated UTIs in children?

The consequences are extremely variable. At one extreme are children with severe pyelonephritis and septicaemia where non-treatment is likely to prove fatal. At the other extreme, a Swedish study in the 1980s found that asymptomatic bacteriuria was as common as clinical pyelonephritis and that in most of the affected children the bacteriuria resolved spontaneously, sometimes after many months5.

The combination of infection and obstruction – such as pelvi-ureteric junction obstruction – can rapidly destroy a kidney. Chronic, low-grade inflammation in any site can cause failure to thrive and UTI is no exception.

Pyelonephritis can cause renal scarring and early treatment can minimise the risk.

Perhaps the biggest concern is that a UTI is a very common presentation for many potentially serious urological abnormalities. Failure to recognise the UTI leads inevitably to failure to diagnose and correctly manage the underlying abnormality.

9 On an MSU result, how do you distinguish between a true infection and a ‘contaminated' urine sample?

Normal human urine can support the growth of E. coli to a concentration of up to 109 organisms/ml. Voided or catheter samples will almost invariably be contaminated by urethral or perineal organisms in small numbers. If left in a plain container at a warm temperature these can multiply rapidly, yielding apparently ‘significant' growth.

So urine should either be refrigerated or collected in a container with borate as a preservative if it is likely that there will be a delay in processing the specimen.

True UTI is generally characterised by pyuria, so a low white cell count in the urine suggests contamination. The presence of significant numbers of squamous cells indicates that the urine was collected using poor technique and is likely to be contaminated with vaginal bacteria.

Culture of more than one organism is suggestive of contamination, as is a single organism in low numbers.

10 How do you distinguish clinically between upper UTI (pyelonephritis) and lower UTI?

The gold standard for diagnosing pyelonephritis is an acute DMSA renal scan. But although this is an extremely valuable research tool it is not recommended in routine practice.

Another investigation that has been useful is the plasma procalcitonin concentration, which correlates well with DMSA changes. Leukocytosis and elevations of C-reactive protein and ESR have proven less reliable.

The clinical picture, although rather less accurate, is widely relied on in practice. High fever and loin or abdominal pain with renal angle tenderness indicate pyelonephritis. Patients with a normal body temperature or low-grade fever are likely to have cystitis only. Infants under three months of age should be regarded as having pyelonephritis with or without bacteraemia and treated with intravenous antibiotics.

Dr Rodney Gilbert is consultant paediatric nephrologist at the Regional Paediatric Nephro-Urology Unit, Southampton General Hospital

Competing interests: none declared

What I will do now What I will do now

Dr Sabby Kant considers the responses to his questions

I think this is a very important update as the key concepts in the management of UTI in children have changed considerably over the past 10 years. Anatomically, it's easy to see why girls are more at risk but interesting to note that boys are at considerably greater risk in infancy.
It is helpful to be reminded that not only is resistance to amoxicillin on the rise, but also to trimethoprim. And on a practical note it is important to dipstick test urine as soon as possible in order to minimise the risk of contaminants brewing nitrates.
I think it's also important to be aware that children over six months with an uncomplicated UTI that responds within 48 hours do not need to be sent for imaging.
Managing other patients depends upon age and whether the patient ‘responds well' or has ‘atypical UTI' or a ‘recurrent UTI'. So it is useful to have definitions of these terms as some investigations will need to be done during the infection phase. Antibiotic prophylaxis has a much lesser role than vigilance and prompt treatment of infection.
Dr Sabby Kant is a GP in Hillingdon, Middlesex

thps Swollen left kidney in boy with UT obstruction

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