Objective Describe the etiologies and clinical characteristics of febrile infants with a bulging fontanelle.

Methods Medical charts of all infants aged 3-18 months who underwent a lumbar puncture during the years 1/2000–2/2008 were identified. One hundred fifty three infants who had a bulging fontanelle and fever were included in the study. General status on admission referred to the worst description from the emergency department or pediatric ward.

Results One infant had bacterial meningitis. History was positive for anorexia, vomiting and restlessness. On physical exam she was described as septic looking and lethargic. Blood count revealed leukopenia and neutropenia. CSF culture was positive for streptococcus pneumonia.

Other diagnoses were: aseptic meningitis (26.7%), upper respiratory tract infection (18.3%), viral not otherwise specified (15.6%), roseola infantum (8.5%), acute otitis media (AOM) (6.5%) and pneumonia (4.5%). The general appearance on presentation of 113 (73.8%) infants was described as good to excellent. Neither one of these infants had bacterial meningitis. Thirty two had aseptic meningitis and 17 had other bacterial disease (pneumonia, AOM, pyelonephritis, bacteremia, shigella or salmonella gastroenteritis). The latter infants had upon admission symptoms, signs or lab tests that suggested a bacterial etiology: bloody diarrhea, AOM, pyuria, elevated leukocyte count on CBC or focal infiltrate on chest X-ray.

Conclusions In well appearing infants, in whom there is no suspicion of a bacterial disease, it is reasonable to observe the infant and withhold a lumbar puncture. Prospective controlled studies should be done in the future in order to confirm this approach.