I had always heard, from a number of sources over the years, that the ratio of death by wounds was one third to one fourth of the deaths by disease. I was surprised this may not always be the case. The 18th Georgia had 184 men killed in battle, and 180 die of disease, including my GGF. There were 533 wounded, among them my grat uncle Frank, wounded twice.
http://homepages.rootsweb.ancestry.com/~allenatk/history.html
A study of Michigan units also found a closer ratio. See this site: http://www.civilwarnews.com/watchdog/wd_100901.html
The ratio was 2.4 to one, disease to battle deaths. This was a much larger sample, and the ratio varied depending on conditions. So, as the man said, "It all depends..." Stan