Just half of babies under three months of age who have potentially deadly bacterial meningitis show symptoms of the fever which, for decades, has been the trigger for further medical investigation, according to new research.
Other features associated with meningitis in infants, such as a bulging fontanelle - the gap on the top of skull where the bones have not yet come together - coma, seizures and neck stiffness, were found to be uncommon.
Clinical presentation in young babies is often non- specific and hard to distinguish from mild illnesses, said the study by St George's, University of London, which looked at infants in the UK and Ireland.
Common features were found to be poor feeding, lethargy and irritability, the findings revealed.
Doctors are in danger of missing deadly bacterial meningitis as they may assume infants without a fever do not have the illness.
There are around 200 cases of bacterial meningitis and septicaemia every year in Ireland and they can kill within hours or cause serious, life-long disabilities if not treated in time.
As many as one in 10 of those affected will die and a third of survivors will be left with after-effects, some as serious as brain damage, amputations, blindness and hearing loss.
Since December 2016, all babies born on or after October 1 that year are routinely vaccinated against the B strain of meningitis. No catch-up was introduced for older children.
Prof Paul Heath, one of the study investigators at St George's, University of London, said: "The classic features of meningitis were uncommon in many cases. The symptoms displayed by young infants when they are seen by doctors at first in hospital are often non-specific and only half of cases showed signs of a fever.
"Guidelines focusing on serious infections in children - including meningitis - have been introduced in the UK and the USA but all specify fever as a key feature of infection.
"Unfortunately, neither the rates of bacterial meningitis in babies, nor the numbers of deaths, has changed since the 1980s.
"Clinicians must, therefore, still consider bacterial meningitis in the diagnosis of an unwell infant that doesn't present with fever."
The study, 'Clinical Characteristics and Risk Factors for Poor Outcome in Infants Less Than 90 Days of Age with Bacterial Meningitis in the United Kingdom and Ireland', is published in the 'Paediatric Infectious Diseases' journal.
The study, which was funded by the charity Meningitis Research Foundation, involved 263 infants across the UK and Ireland and found that fever - a temperature above 38C - was reported in only 54pc of cases, seizures in 28pc, bulging fontanelle in 22pc, coma in 6pc and neck stiffness in only 3pc.
Babies under three months of age are 70 times more likely to get bacterial meningitis than adults. Newborn babies are at the highest risk of all.
The study found that infants who did present with fever tended to be older than infants without fever. The median age for this symptom was around 21-days-old.
The research suggests there should be a low threshold for performing investigations on young infants when they arrive at hospital.
A spokeswoman for the meningitis charity said: "Young babies are particularly vulnerable to meningitis."
Its teaching package, including the eTool and Babywatch, can be accessed at www.meningitis.org/HCPresources.