Hello Judith, I think you are in the ballpark with your thoughts. Here is a good article, but I would add that this concept was not purely Southern.

"Contemporary physicians and others, however, lived with many forms of "the fever" and were fascinated by their local origin, timing, and relationship: swamp fever, country fever, summer fever, bilious fever, broken bone fever; remittent, intermittent, recurring fever. By the nineteenth century, epidemic yellow fever, too, was seen by most Americans as a southern disease entirely. The turning of the southern seasons, the very lay of the southern land, were more than mere backdrop; they were part of fever's very identity. In this way, fever stood for all disease."

You can read the entire article at:
http://uncpress.unc.edu/chapters/stowe_doctoring.html

Sickness and Health in a Southern Place