When my friend's 4-week-old baby developed a fever, she was admitted to the hospital, where they did blood tests and a spinal tap to see if she had meningitis. The procedure upset my friend a lot. Was it really necessary?
Yes. Meningitis is an infection and inflammation of the meninges, which is the lining that surrounds the brain and spinal cord. The proximity of these membranes to the brain makes this infection potentially very dangerous: It can cause serious residual damage and, though rarely, death. The viral type is much less serious and, fortunately, much more common.
Because evaluating a fever in a very young baby is difficult, most doctors agree that the safest approach is to assume the worst and perform a spinal tap. (This is true for older babies, children and adults as well.) The procedure involves inserting a needle between two vertebrae to withdraw fluid for evaluation. While it's understandably upsetting to parents, it is safe.
To be on the safe side, I usually treat with antibiotics until the results of the spinal tap are known.