Urinary Tract Infection in Infancy
A 4-month-old formula-fed girl has 4 days of intermittent non-bilious vomiting, poor feeding, and irritability, and the urine in her nappy is dark and offensive smelling. Her temperature is 38.6 °C and her weight has fallen 300 g in 2 weeks. The abdomen is soft with no palpable mass or visible peristalsis, and there is no rash or focal source of infection. Which is the most likely diagnosis?
- A.Urinary tract infectionCorrect
- B.Diabetic ketoacidosis
- C.Cyclical vomiting syndrome
- D.Nephrotic syndrome
Explanation
Urinary tract infection is the classic great imitator of infancy, because young infants cannot localise symptoms and instead present with non-specific fever, vomiting, poor feeding, irritability, poor weight gain, or prolonged jaundice. A change in urine colour and odour together with fever and vomiting, in the absence of any other identifiable source, points strongly to the urinary tract, and infection is far more common than any of the alternatives at this age. Diagnosis requires a properly collected specimen, meaning catheterisation or suprapubic aspiration in an infant, sent for dipstick, microscopy, and culture before antibiotics. Diabetic ketoacidosis can present at 4 months but is exceedingly rare in that age group and would be accompanied by Kussmaul breathing, marked dehydration, hyperglycaemia, and ketosis rather than isolated urinary odour. Cyclical vomiting syndrome is a diagnosis of exclusion typically starting between 3 and 7 years, characterised by stereotyped self-limited attacks of vomiting separated by entirely symptom-free intervals, and it does not cause fever. Nephrotic syndrome presents with periorbital and dependent oedema, heavy proteinuria, and hypoalbuminaemia, none of which is described, and its peak onset is between 2 and 6 years. Because febrile infection at this age carries a real risk of pyelonephritis and renal scarring, empirical antibiotics should follow specimen collection, with a renal ultrasound arranged as the initial imaging study.
Why each option
- A.
- Correct. Urinary tract infection in infancy presents non-specifically with fever, vomiting, poor feeding, and malodorous or discoloured urine.
- B.
- Diabetic ketoacidosis is very rare at 4 months and would include Kussmaul breathing, hyperglycaemia, and ketosis.
- C.
- Cyclical vomiting syndrome begins in the preschool to school years, is afebrile, and features completely symptom-free intervals.
- D.
- Nephrotic syndrome causes oedema with heavy proteinuria and hypoalbuminaemia and typically presents between 2 and 6 years.
Reference: Nelson Textbook of Pediatrics, 22nd ed., 2024; AAP Clinical Practice Guideline, Urinary Tract Infection in Febrile Infants and Young Children, reaffirmed 2024
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