Urinary tract infections and malformations

18.1 Urinary tract infections and malformations



Colin Jones, Joshua Kausman



Urinary tract infections


Urinary tract infection (UTI) is the second most common bacterial infection affecting children. UTI can cause septicaemia or chronic ill-health with failure to thrive, and is often an indication of an underlying urinary tract malformation.



Epidemiology


Epidemiological studies have shown that 2% of boys and 8% of girls have had a UTI by the age of 7  years; 75% of UTIs occur under the age of 1  year in males and 50% under the age of 1  year in females. The prevalence of UTI in febrile infants under the age of 3  months presenting to emergency departments is 20–30%, and boys outnumber girls. After the age of 3  months, the prevalence of UTI in febrile children falls to around 8% in female and 2% in male children. The incidence of UTI in uncircumcised boys is 4–10 times that in circumcised boys in the first 3  months of life. Common clinical patterns of UTI are described in Table 18.1.1.



Table 18.1.1 Common clinical patterns of urinary tract infection

image


Diagnosis


The frequency of symptoms of UTI in a recent series of 304 children less than 5  years of age presenting to a Sydney hospital emergency department is listed in Table 18.1.2. The presentation varies with age because of the developmental status of the child. Although a wide range of symptoms can occur, an infant will probably have an acute illness with fever and vomiting or a chronic illness with failure to thrive, reflecting the systemic response to infection at this age. The preschool child, who has usually achieved continence, will often show wetting or frequency, complain of generalized abdominal pain and sometimes indicate dysuria. The teenage girl will usually present with symptoms of cystitis (fever, frequency, dysuria, strangury and accurately localized pain) or pyelonephritis (fever, often with rigor, and loin pain and tenderness). At any age, symptoms of fever, vomiting and systemic unwellness occur with pyelonephritis.


Table 18.1.2 Frequency of symptoms in children under 5  years with symptomatic urinary tract infections






















































Symptom %
History of fever 79.6
Axillary temperature > 37.5 °C 59.5
Irritability 52.3
Anorexia 48.7
Malaise/lethargy 44.4
Vomiting 41.8
Diarrhoea 20.7
Dysuria 14.8
Offensive urine 13.2
Abdominal pain 13.2
Family member with past history of UTI* 11.2
Previous unexplained febrile episodes 10.5
Frequency 9.5
Urinary incontinence† 6.6
Macroscopic haematuria 6.6
Febrile convulsion 4.6

UTI, urinary tract infection.


*  First-degree relative.


†  Defined as a noticeable increase in the frequency of daytime wetting.


Source: Craig JC, Irwig LM, Knight JF et al 1998 J Paediatr Child Health 34:154–159.



Urinalysis and microscopy


Microscopy for bacteria with Gram stain has the highest accuracy for rapid detection of UTI (sensitivity 91%, specificity 96%) but requires laboratory facilities. The finding of a positive urinary dipstick test for leukocyte esterase is sensitive for urinary infection (approximately 80% of urine infections detected) and urinary nitrite testing is specific (97% of positive tests indicate infection). Taking the prevalence rates for urine infection at different ages (see Epidemiology) into account, positive tests for both nitrites and leukocyte esterase in a child under 3  months of age predicts a 90% chance of a urine infection. Negative rapid test results are found in 10% of infants with infection. This is not good enough to use negative tests to exclude urinary infection for clinical purposes, because the diagnosis would be missed in a significant number of ill infants. In a child aged 3 years or more or in a circumcised male, the prevalence of urine infection is much lower and the finding of negative tests (leukocyte esterase and nitrites) is reassuring as there is then only a 1% chance of urine infection. Thus, negative test results are quite useful in this older age group in excluding urinary infection and at least justifying withholding antibiotic treatment until the results of urine culture are available.


Microscopy will usually reveal leukocytes and non-glomerular red cells (red cells that appear normally haemoglobinized and of uniform size and shape under phase-contrast microscopy) in freshly examined urine. The presence or absence of bacteria on microscopy can be unreliable: the presence of bacteria on microscopy of a fresh, well collected specimen (e.g. by suprapubic aspiration of urine) can be sensitive and specific for UTI, particularly if the white cell count is high (more than 10 white cells/μl). The finding of epithelial squamous cells indicates a poorly collected sample, and the absence of leukocyturia in a sample with mixed growth or low colony count on culture may indicate a contaminated sample.


Urinary nitrite tests are frequently used to monitor the urine of children prone to recurrent UTI (e.g. continent children with vesicoureteric reflux). Nitrite testing of early morning urine on a weekly basis has been reported to detect UTI in asymptomatic children, enabling treatment to be initiated earlier than would otherwise occur.



image Practical points



Dipstick testing




• Positive leukocyte esterase is a reasonably sensitive test but is not at all specific for urinary tract infection (UTI).


• Positive nitrites are less sensitive but quite specific for UTI.


• Negative testing for leukocyte esterase and nitrites does not exclude UTI, especially in babies. Some 10% of babies with UTI will have negative dipstick testing.


• Always send urine for culture if UTI is suspected.


• Negative dipstick testing may reasonably be used in making the decision to withhold antibiotics from children over 3  years of age while awaiting urine culture results.



Urine culture


Urine culture is the ‘gold standard’ for diagnosis, but management decisions often have to be made before the results are available.


The five common forms of urine collection are compared in Table 18.1.3.



Table 18.1.3 Comparison of methods of urine collection

image


Microbiology


Escherichia coli accounts for 80–90% of pathogens isolated. Proteus species are the cause of infection in 30% of boys over 1  year of age. Coagulase-negative Staphylococcus species are common in teenagers and Klebsiella is frequent in the neonatal period. Pseudomonas species are frequently isolated in children with more complicated anatomical malformations and in those who have had surgical procedures, especially where foreign materials (e.g. urinary stents) have been left in situ. Enterococci cause around 5% of UTIs and are the most common organism found that is resistant to gentamicin. Approximately 5% of children have two organisms isolated. Viral causes of infection have been thought to be rare in children who were not immunosuppressed, but recent urinary polymerase chain reaction (PCR) testing for adenovirus has shown a number of children with classical symptoms and often macroscopic haematuria have this cause.



Initial treatment


Once the urine culture has been obtained, a decision on acute treatment must be made. Intravenous therapy is required if: the child is systemically unwell (dehydrated, signs of septic shock such as hypotension, tachycardia and decreased conscious state); vomiting and unable to retain oral medications; and in infants under the age of 6  months generally, because oral absorption is unreliable. In the child in whom an infection is likely on the basis of urinalysis and presentation, and the child is reasonably well (generally older and not vomiting), oral antibiotics may be commenced, with review once the culture is through in 24–48  hours. In the child in whom urinary infection is a possibility and the child is not unwell, culture results should be awaited before starting treatment. The intravenous antibiotics and oral antibiotics used acutely are listed in Table 18.1.4. Intravenous antibiotics are usually ceased within 2–3  days once culture results have been obtained and the child has improved clinically. Acute treatment is completed with oral antibiotics, usually of 5  days’ duration.


Table 18.1.4 Antibiotic treatment of urinary tract infection









































































Antibiotic Dose Organisms sensitive* (%)
Acute    
Intravenous    
(sick, < 6 months old, pyelonephritis)    
1. Benzyl penicillin 50 mg/kg (max. dose 2 g) 6 hourly Covers Enterococcus
and    
2. Gentamicin 7.5 mg/kg daily for age < 10 years, 6 mg/kg daily for age > 10 years (max. dose 360 mg)
Monitoring: trough level < 1 mg/L taken on 3 rd day and serum creatinine 3 rd day		 ≥ 95
Oral
Trimethoprim 4 mg/kg (max. dose 150 mg) 12 hourly ≥ 85
or
Co-trimoxazole (40 mg/200 mg per 5 mL) ≥ 85
0.5 mL/kg (max. dose 20 mL) 12 hourly
or
Cefalexin 15 mg/kg (max. dose 500 mg) 8 hourly 95
or
Augmentin† 10–25 mg/kg 8 hourly 95
Prophylactic
Co-trimoxazole (40 mg/200 mg per 5 mL) ≥ 85
0.25 mL/kg nightly
Nitrofurantoin 1–2 mg/kg nightly ≥ 85
Cefalexin‡ 5 mg/kg nightly ≥ 95

*  Percentage of bacteria causing urinary tract infection diagnosed in the emergency department of major Australian hospitals that are sensitive to antibiotics.


†  Amoxicillin alone only covers 60% of organisms encountered, so Augmentin is preferred.


‡  The suspension forms of the cephalosporins and penicillins lose activity after a few weeks.

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Aug 4, 2016 | Posted by in PEDIATRICS | Comments Off on Urinary tract infections and malformations

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