Febrile 5-week-old infant in a busy emergency department
A 5-week-old boy is brought to the emergency department at 2 am with a rectal temperature of 38.4°C. He was born at term, had an uncomplicated delivery and has received only the vaccines scheduled at birth. For the past 12 hours he has fed poorly, been sleepy and had fewer wet nappies. On examination he is lethargic but consolable, heart rate 180/min, respiratory rate 50/min, capillary refill 2 seconds, anterior fontanelle flat. There is no rash. His mother has a recurrent cold sore on her lip. Urine output has been nil for 6 hours. The department is busy and the paediatric ward has one isolation bed. The mother is exhausted and asks if she can take him home after blood tests.
1. What investigations would you order, and what empirical antibiotics would you start? Justify your choice.
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- Sepsis screen before antibiotics: blood culture, catheter urine culture, FBC, CRP, glucose, lactate, electrolytes, renal and liver function, clotting. Lumbar puncture if stable. Chest X-ray only if respiratory signs.
- Empirical IV antibiotics: ampicillin 50 mg/kg plus cefotaxime 50 mg/kg (or ceftriaxone) to cover group B Streptococcus, E. coli and Listeria. Add gentamicin only per local protocol.
- Add aciclovir 20 mg/kg IV every 8 hours if HSV risk is considered significant (maternal cold sore, seizures, vesicles, raised transaminases).
- Rationale: at 5 weeks the infant has immature immunity and is at risk of late-onset GBS and Gram-negative sepsis; Listeria coverage is still recommended in this age group.
- Do not delay antibiotics for the lumbar puncture.
2. Should a lumbar puncture be performed now? What about testing and treating for herpes simplex virus?
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- Perform LP now if he is stable, has no coagulopathy, no cardiorespiratory instability and no local skin infection. It is the only way to confirm meningitis and guide duration.
- If LP is deferred, start antibiotics first and perform LP when safe; document the reason.
- HSV: maternal cold sore is a risk factor, but at 5 weeks HSV encephalitis is uncommon. Send CSF HSV PCR, surface swabs and maternal lesion PCR. Start aciclovir if there are vesicles, seizures, focal signs, raised LFTs or CSF pleocytosis.
- Do not perform LP if there is shock, respiratory compromise or coagulopathy; treat empirically.
3. What is your disposition plan, and how would you counsel the mother?
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- Admit for at least 48 hours for observation and culture review; use the isolation bed if HSV is suspected.
- If he remains well, cultures are negative at 36–48 hours and feeding is established, discharge with clear safety advice.
- Counsel the mother: return immediately if fever, poor feeding, lethargy, irritability, rash, breathing difficulty, seizures or reduced wet nappies. Explain that blood tests alone cannot exclude serious bacterial infection at this age.
- Arrange follow-up and document the discussion.