That depends on how serious the consequences of the disease could be.
In the 1920s, 77 of 78 children at Boston Children's Hospital who had Haemophilus influenzae meningitis died. The prognosis for untreated pneumococcal meningitis was equally bleak: of 300 patients, all died. In the first decade of the 20th century, untreated meningococcal meningitis was associated with a mortality rate of 75 to 80 percent.