All his books are listed here http://www.fantasticfiction.co.uk/g/richard-go rdon/
The only other one about Cholera I can think of is
The Medical Detective.
John Snow and the Mystery of Cholera by Sandra Hempel
JOhn Snow the Cholera fella was also anaesthetist and it is possible that cholera is treated in any of the non fiction books listed.
I mean it makes a good story - J SNow noticed some old bat in a non cholera area got it, and learnt that she shipped in her water from her old childhood area (high cholera)
I've checked out all the books on the "fantasticfiction" site and none of those listed seems to be the book I'm looking for. Friend swears she hasn't made a mistake about author or topic. Many thanks for you help!