Urinary Tract Infection (UTI) in Pediatric

The urinary tract is a common site of infection in children. The annual incidence is up to 1% in girls, but less common in boys. Radiological abnormalities are present in about 40% of children with UTIs, the most common being reflux. Asymptomatic bacteriuria in schoolgirls is about 1–2%. It is often difficult to diagnose a UTI on history or examination alone in children and a high index of suspicion must be held. The consequences of missing a UTI in a child with even minor urinary tract abnormalities may be significant.

Positive dipstick for leucocytes and nitrites in a sick child does not exclude another site of serious infection (e.g. meningitis). Organisms may also spread from the urinary tract to elsewhere including the meninges. Therefore further investigations as part of a septic work-up (e.g. LP) should not be omitted in a sick child who returns a positive dipstick.

Source pict: http://www.tipdisease.com/2013/12/urinary-tract-infection-in-children.html

History

Symptoms of serious urinary infections are often non-specific and include fever, irritability, poor feeding and vomiting. More specific features may include loin or abdominal pain, frequency and dysuria. These localising signs are often absent in younger patients. Some children with UTIs may look quite well, while others may appear very unwell.

Examination

This is often normal other than the presence of fever. Loin or suprapubic tenderness may be present. Urinary dipstick testing is only a screening test for a UTI. It has poor sensitivity and specificity (see below).

Initial investigations

A UTI cannot be diagnosed on symptoms alone, nor by culture of urine from a bag specimen. A definitive diagnosis can only be made by culture of urine obtained in a sterile fashion from a mid-stream urine (MSU), suprapubic aspiration (SPA), or a catheter specimen of urine (CSU). Prior antibiotic therapy may lead to negative urine culture in patients with UTI. The laboratory will test for antibacterial activity in the urine. Any child who is unwell or is under 6 months old should also have blood culture and electrolytes tested and should be considered for lumbar puncture.

a. Dipstick urine tests

Dipsticks can detect urinary protein, blood, nitrites (produced by bacterial reduction of urinary nitrate), and leucocyte esterase (an enzyme present in white blood cells). They are a screening test only. If you really suspect UTI you must send a specimen for microscopy and culture. Blood and protein are unreliable markers of UTI. Not all organisms produce nitrites and nitrites take time to develop in urine and so have poor sensitivity. Nitrites may appear in the urine in the presence of infections in other body systems.

Not all patients with UTI have pyuria. Leucocyte esterase can only be detected with relatively high WBC counts in urine, so the test has low sensitivity. Leucocytes from local sources (vagina, foreskin) may contaminate urine. Leucocytes appear in the urine in many other febrile illnesses, e.g. upper respiratory tract infection, pneumonia, etc. So the specificity is low. Overall combined sensitivity for both nitrites and leucocytes is around 50%, i.e. dipsticks may miss 50% of infections.

b. Urine specimen collection

There are several ways to collect urine specimens in children, each with its benefits and problems. Practice differs around the world. In the UK, SPA is the method of choice in

infants if a clean catch specimen is not possible. However, in North America, SPA is rarely practised. Parents are offered a choice between awaiting bag screening, confirmed

by CSU on positive specimens, or immediate catheterisation. 

- Urine bag. A urine bag is useful for collecting urine for screening purposes in children who cannot void on request (approximately 0–3 years). The genitalia should be washed with water and dried before application of the bag. Urine is tested with a dipstick for leucocytes and nitrites. If it is positive for either, you should obtain a definitive specimen by SPA (or CSU if SPA fails). If clinical suspicion is high, send a definitive specimen for culture regardless of the dipstick result. A negative dipstick result does not exclude a UTI. Do not send bag specimens for culture in acute presentations. Antibiotics should not be given unless a definitive urine specimen has been obtained.

- Suprapubic aspiration (SPA). SPA remains the preferred method in the UK to collect a minimally contaminated specimen. It should be considered in children too young to obtain an MSU, and with a high probability of UTI, or who are unwell and who warrant a more invasive investigation. The child should be offered fluid to drink. Bedside ultrasound equipment, if available, can improve the success rate of SPA by detecting a full bladder. One author reports 60% success collection rate of SPA and this increases to 80% if bladder ultrasound is used. The specimen should be screened with a dipstick and then sent for culture. Any growth from SPA urine usually indicates infection (but note possible contamination by skin commensals and fecal flora may occasionally produce a mixed growth).

- Catheter specimens. These are useful if SPA fails. The first few drops of the specimen should be discarded and the remaining specimen should always be sent for culture. Any growth of over 103 organisms per ml indicates infection. 

- Mid-stream urine (MSU). A mid-stream urine can be obtained from children who can void on request. The genitalia should be washed with water and dried before the specimen is taken. The first few millilitres should be voided and not collected and then a specimen is obtained. A pure growth of over 108 organisms per ml indicates infection. Apure growth of over 105 organisms per ml may indicate early infection and requires a repeat 

Treatment of UTI

Antibiotics may be given orally or intravenously for a UTI. Oral medication is appropriate for those over the age of 6 months who are not systemically unwell. Cotrimoxazole (200/40 mg in 5 ml) 0.3 ml/ Kg weight b.d. orally for 1 week is a suitable antibiotic. Alternatives include cephalexin 15 mg kg−1 (500 mg) orally three times a day. Any child who is unwell, and most children under 6 months, should be admitted for i.v. antibiotics. Treatment options vary around the world but suitable regimens include cefuroxime 50 mg/Kg weight per dose (maximum 2g) or gentamicin 7.5 mg/Kg weight (maximum dose 240 mg) i.v. daily and benzylpenicillin 50 mg/Kg weight (maximum dose 3 g) i.v. 6 hourly for children over 1 month of age. Gentamicin levels should be taken to ensure appropriate time between subsequent doses. All children should have antibiotic sensitivities checked at 24–48 hours and therapy adjusted accordingly. For children who are still in nappies a prophylactic dose of antibiotic, e.g. co-trimoxazole (200/40 mg in 5 ml) 0.15 ml/Kg weight in a single daily dose, or nitrofurantoin 3 mg/Kg weight at night should be maintained until the child is seen for follow up. If the child is not settling, repeat the urine culture to determine eradication of organism. A shocked child will require fluid resuscitation. Any child with underlying urinary  tract abnormalities should be discussed with the registrar or consultant.

Follow up investigations

All children with proven UTI should be referred for follow up in the general pediatric clinic, or by the child’s own pediatrician. All those with their first UTI should have a renal ultrasound. A micturating cysto-urethrogram (MCU), abdominal X-ray and DMSA (dimercapto-succinoacetic acid) scan may be necessary, but the decision needs to be considered on an individual basis. They are usually done in children under 1 year of age, and may be necessary for older children according to circumstances. For older children, discussion of the need for MCU should be deferred to the outpatient follow up visit.