Not necessarily. My daughter had not had contact with anyone who had meningitis. Of course, she was reported to the health department for monitoring. Her pediatrician took to calling her the "World Famous Baby". She recovered beautifully, except that her teeth were a little damaged from the week of heavy-duty antibiotics. We caught it early.
Doctors don't mess around with infants this young who present with a high fever and irritability. As an earlier poster pointed out, they can't complain of the classic symptoms of stiff neck, light sensitivity, headache.