And just how did he get meningitis? Nevermind, I don't think I want to know...
A little squeamish? Shopping cart, door handle, anything someone with a bacterial infection might have touched and deposited germs on. Or possibly as a secondary infection following an upper respiratory infection or ear infection.
From the web, Medical Microbiology:
Human immunodeficiency virus can cause acute and progressive CNS disease. HTLV-I causes chronic spastic paraparesis in a small number of infected persons."
One of many possibilities along with other STDs or simple bacterial infection.