@damYankee I believe we may be agreeing more than differeing
I was pointing out that the big city boys---New York, Chicago, Philadelphia and Boston to mention a few---were exposed to several diseases before the country boys and so the rural soldiers were hit the hardest in camps. I have read several articles and a few books dealing with health concerns about soldiers and will share an article below that states my view better than I can.
Regards
David
"Socioeconomic background affected soldier's chances of survival during the Civil War in the areas of previous residency, occupation and skin color for blacks. The mortality of a white Northern solider was better if he was not a farmer and lived in the city because he was probably exposed to other infections and his body had built immunity to the disease. The mortality from disease for slaves formerly engaged in other nonfarm occupations such as house servants was as low as the death rate for those in elite occupations, but their advantages over field hands resulted exclusively from their lower probability of contracting diseases."
The Impact of Disease on the Civil Ware by Intisar K. Hamidullah
https://teachers.yale.edu/curriculum/viewer/initiative_10.06.02_u