There is a distinct form of literary genre called Southern Gothic, which is of course derived from standard American Gothic literature.

Within the larger genre, the macabre, occult, and paranormal interact with the natural world. The classic example of American Gothic would be works by Edgar Allen Poe, The Tale of the Headless Horseman, etc.

With Southern Gothic, you have a unique twist in that it is less "spooky demons" and evil men, and more of a social commentary. Writers such as William Faulkner focused more on peeling away the cultural illusions of the Deep South. Behind the facade of gentile culture, sophistication, and religious morality, there lay a dark heart of people. Themes of decay, betrayal, hidden immoralities, suppressed violence, cults of silence along the lines of "just ignore it and it will go away", and social conformity are strong themes in this genre.

Examples of this genre would include (all these links have spoilers) A Rose for Emily by William Faulkner, Orpheus Descending by Tennessee Williams, for two good examples. You can include Harper Lee, Eudora Welty, and by some arguments some of Mark Twain's darker works.

Most of these writers come from the early and mid 20th Century, but in recent years writers like Anne Rice have popularized south Louisiana and cajun culture mostly due to it's relatively alien nature to the mainstream American. Many people describe New Orleans as "The most European city in America" in its culture and values that tend to lean more French and "old Spanish" (as opposed Latino Spanish such as the Southwest), as opposed to Northern European and English like much of the rest of America.

Even today there are wide swaths of extremely poor and isolated communities of French speaking (as a primary language) people. Cultural mixtures of Spanish, French, Slave (African), and Native American has created a unique culture in the area. With the importation of slaves into the areas plantations from West Africa and carried over from Haiti, an extension of Voodoo grew in the area, which added to the exotic nature (comparable to the existence of Santeria in Southern Florida).

This combination has created a unique atmosphere to allow writers to create new takes on old stories such as vampires, macbre and twisted stories about cultural ostracism and cultish behaviors, and stories about cultural conformity and hidden desires and secrets.

Modern focus on South Louisiana is merely an extension of this Southern Gothic style into a specific region to give it a unique flavor. Think of this as similar to Steven Kings visions of small town New England and it's Lovecraftian conflicts of class, values, and moral decay.