A five-week-old with a temperature of 38.4 °C and mottled skin
A 5-week-old boy is brought to the emergency department at 02:00 with a rectal temperature of 38.4 °C recorded at home an hour ago. He was born at term, weighed 3.4 kg, had an uncomplicated delivery and went home at 48 hours; the mother reports no fever, no prolonged rupture of membranes and no group B streptococcus carriage. He has taken half his usual feed volume for two feeds and has been sleepier than usual. Examination: weight 4.1 kg, HR 168, RR 52, BP 78/48, capillary refill 3 seconds with mottled extremities, anterior fontanelle soft, no rash, no focal signs, abdomen soft. He is alert and cries during venepuncture. Urine dipstick is negative for leucocytes. The paediatric resident proposes sending blood and urine cultures, giving intramuscular ceftriaxone 50 mg/kg, observing for four hours and discharging if cultures are negative at 24 hours.
1. Identify the errors in the resident's plan and set out the correct evaluation and disposition.
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The plan is wrong on three counts: the observation period is too short to exclude serious bacterial infection; a lumbar puncture and cerebrospinal fluid analysis are missing; and this infant is not well enough for any discharge pathway regardless of age.
Age band. At 5 weeks (35 days) he falls in the 29–90 day group, where a well-appearing infant with a normal urinalysis and reliable follow-up may sometimes be managed with cultures and parenteral antibiotics without admission. That pathway requires a genuinely well infant. This baby has capillary refill of 3 seconds, mottling, tachycardia and reduced feeding and alertness - he is clinically unwell and the pathway does not apply.
Correct evaluation.
- Blood culture and full blood count, CRP, glucose, electrolytes and blood gas.
- Urine by catheter or suprapubic aspirate, never a bag specimen, for culture and microscopy.
- Lumbar puncture once he is stabilised, with cerebrospinal fluid cell count, protein, glucose, Gram stain and culture; if there are vesicles, seizures or a suggestive maternal history, add herpes simplex virus PCR and surface swabs.
- Chest radiograph only if there are respiratory signs; stool culture if there is diarrhoea.
Disposition. Admit, obtain intravenous access, take cultures, then start empiric intravenous antibiotics - ampicillin plus gentamicin, or ampicillin plus cefotaxime, dosed for age. Observe for at least 24–48 hours and reassess when culture results and the clinical course are known. The intramuscular ceftriaxone-and-review model belongs to selected well-appearing older infants with guaranteed 24-hour review.
2. Which organisms are you covering, and how does the infant's age change the cover and the drug choice?
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Under 28 days. Group B streptococcus, Escherichia coli and other enteric Gram-negatives, and Listeria monocytogenes. Ampicillin covers Listeria and enterococcus; gentamicin or cefotaxime covers Gram-negatives. Ceftriaxone is avoided in this group because it displaces bilirubin from albumin (kernicterus risk) and can precipitate with calcium-containing fluids.
29–90 days. Streptococcus pneumoniae, Neisseria meningitidis, group B streptococcus, E. coli and, less commonly, Salmonella. Listeria becomes rare after about four weeks, but many units still include ampicillin in an unwell infant; in this baby, who looks unwell, ampicillin plus cefotaxime (or gentamicin) is reasonable. Ceftriaxone is acceptable at this age; use meningitic doses (ceftriaxone 80–100 mg/kg/day or cefotaxime 50 mg/kg every 8 hours) when cerebrospinal fluid has been obtained or meningitis cannot be excluded.
Beyond three months. Pneumococcus and meningococcus dominate; ampicillin is not routine.
Always consider herpes simplex virus in the first six weeks. Vesicles, seizures, a sepsis-like picture with negative bacterial cultures, or cerebrospinal fluid pleocytosis with a negative Gram stain should prompt intravenous aciclovir in addition to antibacterials, while PCR results are awaited. Getting the age band right matters because it determines whether Listeria cover and whether ceftriaxone are appropriate.
3. The infant becomes mottled and drowsy while the lumbar puncture trolley is being prepared. How does that change the plan?
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Stabilise first. Airway, breathing and circulation take precedence: oxygen, intravenous or intraosseous access, a 10–20 mL/kg crystalloid bolus, glucose check, and continuous monitoring. A lumbar puncture is deferred in an unstable, drowsy infant until after resuscitation; the procedure can precipitate deterioration, especially with raised intracranial pressure or cardiorespiratory instability.
Do not let the deferred lumbar puncture lower the antibiotic dose. Give meningitic-dose cover blind: cefotaxime 50 mg/kg every 8 hours plus ampicillin, and add aciclovir if herpes simplex is possible. Blood cultures should be taken before antibiotics but must never delay them in a shocked infant.
Then continue. Reassess after the bolus, obtain the lumbar puncture when stable, and consider a fluid-refractory shock pathway and involvement of the paediatric intensive care team if hypotension persists. Document explicitly why the lumbar puncture was deferred and when it will be repeated - this is exactly the situation where a note of "LP deferred, meningitic dose cover given" prevents both undertreatment and later criticism.