I agree with Dr Baptist's critique that a smile may not be a 100% accurate test to rule out meningitis in a febrile infant, but I hope no one thought I was failing to obtain a full history and results of a physical examination before deciding whether or not to initiate laboratory studies. My only contention is that in 45 years as a solo suburban pediatrician, I have never yet seen a febrile infant with meningitis who smiled.
However, what test ever is 100% accurate? Even results of an initial lumbar puncture that show CSF free of cells and normal results of chemistry studies do not rule out meningitis. I have examined a 3-month-old infant with purulent otitis media and suspicious meningeal signs whose initial CSF findings were normal, only to be told 12 hours later that the CSF culture was growing pneumococci.
I think Dr McCarthy's reply
Rogers WB. Meningitis in the Child With a Smile-Reply. Arch Pediatr Adolesc Med. 1995;149(10):1179. doi:10.1001/archpedi.1995.02170230133030