Helen Keller became deaf and blind at the age of 19 months after developing a febrile illness. The exact cause of her illness is not clear, but some historians have attributed it to rubella, scarlet fever, or meningitis. Recent analysis suggests that she likely had bacterial meningitis, caused by Neisseria meningitidis or possibly Haemophilus influenzae. While blindness and deafness could conceivably be sequelae of encephalitis, it would likely be accompanied by evidence of severe global cerebral damage, such as intellectual compromise or persistent seizures, which was not the case for Helen Keller. Scarlet fever was also unlikely to be the cause of her deafblindness, as visual and/or hearing loss were extremely rare sequelae of this infection. Despite the lack of a clear diagnosis, Helen Keller went on to become an accomplished author and activist for people with disabilities, who persevered in the face of adversity.