Yes, you’re all right. They suffered from encephalitis lethargica which was epidemic in the 1920s. As far as we know, around five million people died from causes related to it. Its aetiology (=causes) is unclear but a leading theory says that it was caused by streptococcal (paciorkowiec) infection.
What made Dr Sayer administer a medicine for parkinsonian patients to the catatonic, post-encephalitic patients?