Paediatric urinary tract infection

Definition

Infection of the urinary tract. Pretty simple really. Hope this isn't a great surprise to you.

Epidemiology

3% of girls and 1% of boys have a symptomatic UTI before they reach 11, half of whom have a recurrence within 1 year.

Pathophysiology

Generally, the infection comes from outside and travels up the urethra into the bladder. Girls' shorter urethras explain why it is three times more common than in boys. Kidney infection results from the pathogen travelling up the ureter.

E.coli is the most common pathogen and its virulence varies depending on its antigens, endotoxins and P-fimbriae (which are cell wall appendages). Proteus and Pseudomonas are the two next most common pathogen species implicated. Proteus is more common in boys and this is thought to be due to its presence under the prepuce

Risk Factors

Incomplete bladder emptying is a risk factor in UTI. Imagine if you urinated in your toilet and then didn't flush it for quite a few hours. It'd smell good, wouldn't it? Well, that's what happens in your bladder if you don't urinate regularly and it makes UTI more likely. This is can be caused by a variety of factors from the pathological (vesicoureteric reflux obstruction from a loaded rectum, neuropathic bladder) to the more benign (infrequent voiding, hurried micturition). Basically, if there's a suspicion that the bladder isn't being emptied, it's a risk factor for UTI.

Hydronephrosis which is the distention and dilatation of the renal pelvis. It is caused by anything that stops the free flow of urine out of the bladder. The main cause of this is:

Vesicoureteric reflux. In the normal bladder, the ureters enter at such an angle that when the bladder contracts during micturition, urine cannot escape back up the ureters. In vesicoureteric reflux, this doesn't happen and so urine (or "wee" in proper medical jargon) escapes back up the ureters. Thus, this too can be considered a risk factor for UTI

Clinical Features

In adult urinary tract infection, things are much simpler as they will normally have specific urinary symptoms (dysuria). Children, particularly infants, are rubbish for this in that they either can't communicate or cannot, because the pain sensation has not developed properly, localise pain well. The following are features which are possible in children of all ages:

• Fever
• Febrile convulsions
• Tachycardia
• Vomiting/diarrhoea
• Lethargy and irritability
• Poor feeding (possibly failure to thrive)
• Neonatal jaundice
• Sepsis

However, in older children but NOT infants, more specific clinical features can be identified:

• Dysuria
• Frequency
• Rigors
• Abdo/loin pain
• Enuresis
• Haematuria

Investigations

Bloods

• FBC - WCC↑ due to infection
• U+Es - for dehydration
• Blood cultures - exclude sepsis

Urine

• Dipstick

Evidently, testing urine in a UTI seems like an obvious thing to do but young children don't have the capacity to wee into a bucket on demand like adults. (Not like a circus show, mind. I just mean that if you give them a drink, a pot and an hour and they'll generally be fine.) As such there are five different methods:

• a nappy pad which is easy to do but difficult to keep from cross infection due to contaminations from the natural flora of the perineum in both boys and girls
• a 'clean-catch' sample which requires patience and a hell of a lot of luck. You also need to miss the first part of the stream in order that the flora of the urethra don't get into the sample. As such, this should only be done where time is NOT of the essence.
• an adhesive plastic bag can be attached but there's a high chance of conatmination from pernieal flora.
• suprapubic aspirate (SPA) which basically consist of ramming a needle into the bladder through the lower abdomen. Quick, accurate but invasive and traumatic. Useful in an emergency, though.
• catherisation can work but you push all the bugs from the urethra into the bladder which can contaminate the sample. Having a tube pushed into your bladder via your urethra is litte more pleasant than an SPA.

The urine must be then sent for microscopy, sensitivty and culture (M,C&S).

Management

Acute management

Antibiotics - co-amoxiclav orally for 5 days, 10 if the child is still systemically unwell. Change the antibiotics when the sensitivity of the urine culture comes back.

IV therapy is indicated in children who are severely ill using stronger antibiotics (cefotaxime/amoxycillin with gentamicin). Oral therapy is restored when the fever is gone.

Further investigation

A significant proportion of children need to be further investigated for structural abnomalities but which children to do this in remains a controversial topic as the investigations are expensive and invasive. However, children receive an ultrasound of the kidney as this is a cheap and non-invasive investigation.

Triggers for further investigation

These are things that results in further investigation even with a normal ultrasound.

• known antenatal abnormality
• infants
• boys
• >1 UTI
• sepsis
• prolonged clinical course
• fever >48 hours
• FHx of reflux
• organism was not E.coli

High-risk or abnormal ultrasound

What is done depends very much on what the local protocol is so if you want to learn it properly, go and find your local protocols but the following are the possible investigations to rule out a structural abnormality:

• MAG3 - this is the name of the compound which is then radiolabelled so the radiologists can take a look at the kidneys. It is injected intravenously and then the kidneys excrete it.
• MCUG - micturating cystourethrograms involve catherisation in order to fill the bladder with radio-opaque dye. The bladder is seen during micturition and reflux can be identified.
• DMSA scan - a dimercaptosuccinic acid scan will works in a similar way to a MAG3 scan except DMSA is already radio-opaque and so does not need to be radiolabelled to be seen.