This book provides good information for introducing diseases into any RPG. However it is written from a modern perspective, so insights in how healers of the Middle Ages viewed diseases and would have treated them are not included. That has left me a bit disappointed, but it wasn't promised.
The author also has a very high powered world as default setting, where fifth level clerics are abundant even in small communities and fifteenth level clerics common enough for the Heal spell to be considered a standard treatment. As such all magical healing is focused on what really are powerful spells being abundant and no magical treatments short of these spells are included. Again, nothing else was promised, but it's an opportunity lost.
The shortcoming that made me consider giving the product a lower rating was the complete lack of diagnosis section; sure, symptoms are discussed, but some guideline of how likely a doctor is to diagnose the disease correctly or how he could miss-diagnose it would be useful. Likewise treatments for some diseases like Malaria are listed as poisonous, but the health effects of that poison are not discussed.
As such the book falls short of being the definitive work for diseases in fantasy settings, but it remains the best work I have found to date.
[5 of 5 Stars!]