How high does a fever have to be to take a 3 month old back to the emergency room? just left the emergency room at 10pm last night they done a spinal tap and blood work and urine test. he is only three months old i can not give any tylenol fever is 99.9

Assuming : Assuming the er physician felt your infants fever was due to a viral illness, you can observe at home if your infant is alert, eating well, having his usual number of wet diapers every few hours, no breathing difficulty and not fussy or irritable. 99.9 is not considered a fever. No need to give tylenol (acetaminophen) for 99. Always call your regular physician to see if a trip to the er is needed.