Ripped from Warning Sign (1985) -- **SPOILERS**
Warning Sign (1985) http://www.imdb.com/title/tt0090293/combined
has the same basic plot -- germ warfare lab disguised as agro station --
but it's much more developed, as are the characters, and it has
Jeffrey DeMunn in a great role that's totally missing from Patient Zero.
PZ instead is padded with a lot of yakking about a wedding, and being
chased by zombies and murdered by soldiers.
Warning Sign has been allowed to go out of print, but you can find it
on the Net if you know where to look.
Human knowledge belongs to the world!
Antitrust (2001)
http://www.imdb.com/title/tt0218817/combined