A rectal temperature of 38.0°C or above in an infant under three months is an investigation pathway, not a symptom to be interpreted. The reason is that the physical examination in this age group does not reliably separate the infant with bacteraemia or meningitis from the one with a virus: the septic neonate can look unremarkable for hours, and the reassuring examination at 2 a.m. is the one most often regretted.
So the rule is procedural. Under 28 days: full septic screen including lumbar puncture, and empirical antibiotics, regardless of how well the baby looks. Between 28 and 90 days: a full assessment with urine, blood culture and inflammatory markers, with the lumbar puncture threshold set by the markers and by appearance — but low. A clean urine dipstick does not exclude urinary infection at this age; send the sample for culture.
Two specifics that get missed. A history of fever at home counts even if the infant is afebrile in front of you — do not discount it because your thermometer disagrees. And ask about maternal group B streptococcus status, intrapartum antibiotics and prolonged rupture of membranes; in a two-week-old, that history changes the organisms you are covering for.
- Under 28 days: septic screen with lumbar puncture and empirical antibiotics, however well the baby looks
- Take a reported fever at home as real, even if the infant is afebrile on arrival
- Send urine for culture regardless of the dipstick result
- Ask about maternal group B streptococcus, intrapartum antibiotics and rupture of membranes
- Record a clear reassessment interval — deterioration in this age group is measured in hours
Why it matters
The examination that reassures you in a young infant is the least reliable examination in paediatrics.
Read the rest in the app
You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.
Scan to keep reading on your phone. No account needed to start.
Tomorrow morning, before your first patient
One edition a day for paediatrics, written by the desk, every claim tied to its paper. Six minutes.
Get the app — free