How best to diagnose urinary tract infection in preschool children in primary care?BMJ 2011; 343 doi: https://doi.org/10.1136/bmj.d6316 (Published 25 October 2011) Cite this as: BMJ 2011;343:d6316
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Hay and colleagues do, in a recent issue of the BMJ, address the interesting topic how to best diagnose a urinary tract infection in primary care. This is a very important issue as a majority of children with a suspicion of a UTI will first be seen by their GP. There are however a few problems with the authors’ analyses. These problems make their data more difficult to understand and to use in clinical practice. Their recommendations are thus perhaps not totally in the best interest of the child with a suspected UTI.
The authors mention a few major problems in making an accurate diagnosis of UTI in small children – contaminated culture and concurrent asymptomatic bacteriuria (ABU) – but they do not draw any conclusions on how to deal with them. They do also lump all forms of UTI into one which makes any analyses very difficult.
Contaminated cultures are a substantial problem in the diagnosis of any UTI in small children. Hay et al quote a recent study which showed a specificity of 80% for a bag sample compared to a catheter sample.1 This problem is well known since early studies from the 1970s. Varying contaminations rate from 7.5% to 62.8% has been found in different studies.1-4
The biological basis for this contamination is the way that small children pass urine. Small boys have a physiologic phimosis and therefore flush their prepuce when they wee while small girls very often flush their vagina. This is clearly seen on the micturition urethrograms in figures 1 and 2. Many urine samples are thus contaminated when they reach the surface of the child and the urine bag or the urine pad. A clean catch urine sample can be a very good option but it is often not possible in small children and it will not overcome the problem with the physiologic phimosis in the boys. It can help in girls but means that the parents have to sit prepared to take the urine sample while spreading the legs of the girl widely. This is not easy in a febrile crying 9 month old girl!
The very recent guidelines on febrile UTI in children below the age of 2 years from the American Academy of Pediatrics therefore state that bag urine cultures are very unreliable and that they can only be used to rule out a UTI.5 These guidelines emphasise that a urine specimen obtained by a bag applied to the perineum has an unacceptably high false-positive rate and can signify both a true infection and a contaminated culture. They recommend that the urine should be obtained either by a suprapubic puncture or by urethral catherisation.
Asymptomatic Bacteriuria (ABU)
ABU is quite a common in infants. A now quite old study provided urine cultures in all 3581 infants that were born during one year in one specific catchment area. All infants had bag cultures done at two weeks, 3 month and 10 month of age. Positive cultures were always confirmed with a supra-pubic bladder puncture.6
A minimum of 2.5% of the boys and 0.9% of the girls showed ABU during their first year of life, Fig 3 and 4. In the same cohort of children another 1.2% of the boys and 1.1% of the girls developed an episode of febrile symptomatic UTI. Follow-up showed that the ABU lasted between 0.5 and 7.5 month (median 2 month for the girls and 1.5 month for the boys) and cleared spontaneously without out any signs of kidney scarring at six year follow-up.6-8
The need for a level diagnosis
It is important to do a level diagnosis in every case of UTI – febrile upper UTI, lower UTI or cystitis and ABU. A reliable clinical level diagnosis is possible to make in a majority of cases with a UTI. This is essential as these different infections have very different epidemiology, symptoms, treatment and need for follow up.
We would never dream of lumping together tonsillitis, otitis media, a common cold and pneumonia as “respiratory tract infection, RTI, without acknowledging the major differences between these separate conditions.
This lumping of different diagnosis into one is the major reason for some of the author’s “strange” findings. They observed that e.g. neither poor feeding nor vomiting appeared to have a diagnostic value for a UTI. The reason for this is easy to understand if you consider the presentation of children with the different kinds of UTI. An infant with a febrile UTI will very often have poor feeding and vomiting while a typical five year old girl with cystitis will not. And a child with ABU detected when presenting with a febrile viral infection will have no symptoms from the bacteriuria at all. Poor feeding and vomiting are thus only symptoms of one of the three different kinds of UTI, acute pyelonephritis. Similarly voiding pains are mainly a symptom of acute cystitis and not of the other kinds of UTI.
Consequences for recommendations in primary care
The practice recommended by the authors will make the rate of false positive diagnosis of a febrile UTI very high. Calculating from the epidemiology data one of every forth infant boy and one out every sixth infant girl with true bacteriuria and fever will actually have ABU and another infection. If the urine is collected with a bag or a urine pad then the chance of contaminated cultures will increase the number of false positive diagnosis with between 7.5% and 62.8%.
A properly collected urine sample must always be obtained if there are leucocytes in an initial bag sample. It is not accurate to start treatment without a bacterial culture from an uncontaminated urine sample and is equally not accurate to wait for the possibly contaminated urine culture to come back before making a treatment decision.
When the diagnosis of a UTI has been made then a level diagnosis also needs to be established. This will decide which drug to use, how long it should be used and also on the follow-up needed for that child.
The above problems must be taken into consideration when recommendations are made for the diagnosis of a UTI in preschool children. This can make the care of the small children with a suspicion of a febrile UTI difficult in the GP practice but cannot be avoided if the child’s best interest is at centre.
Kjell Tullus MD, PhD, FRCPCH
Consultant Paediatric Nephrologist
(1)Etoubleau C, Reveret M, Brouet D, Badier I, Brosset P, Fourcade L et al. Moving from bag to catheter for urine collection in non-toilet-trained children suspected of having urinary tract infection: a paired comparison of urine cultures. J Pediatr 2009; 154(6):803-806.
(2) Al-Orifi F, McGillivray D, Tange S, Kramer MS. Urine culture from bag specimens in young children: are the risks too high? J Pediatr 2000; 137(2):221-226.
(3)Aronson AS, Gustafson B, Svenningsen NW. Combined suprapubic aspiration and clean-voided urine examination in infants and children. Acta Paediatr Scand 1973; 62(4):396-400.
(4)Hardy JD, Furnell PM, Brumfitt W. Comparison of sterile bag, clean catch and suprapubic aspiration in the diagnosis of urinary infection in early childhood. Br J Urol 1976; 48(4):279-283.
(5)Urinary Tract Infection: Clinical Practice Guideline for the Diagnosis and Management of the Initial UTI in Febrile Infants and Children 2 to 24 Months. Pediatrics 2011.
(6)Wettergren B, Jodal U. Spontaneous clearance of asymptomatic bacteriuria in infants. Acta Paediatr Scand 1990; 79(3):300-304.
(7)Wettergren B, Jodal U, Jonasson G. Epidemiology of bacteriuria during the first year of life. Acta Paediatr Scand 1985; 74(6):925-933.
(8)Wettergren B, Hellstrom M, Stokland E, Jodal U. Six year follow up of infants with bacteriuria on screening. BMJ 1990; 301(6756):845-848.
Competing interests: No competing interests