I think that more than any other category of illness (with the possible exception of cancer) infectious diseases, because of their penchant to be explosive, mysterious, and sometimes deadly, attract faith healers to the scene. It's not surprising since the germ theory of disease has really been an accepted part of medical practice for only about 150 years.
The germ theory supplanted fallacious ideas about the four humors, miasmas, and even the evil eye as well as evil spirits. So it is not surprising that faith healers and mystics had roles in prior plagues, epidemics, and pandemics. Even in the modern era, witch doctors were prominent in the West Africa Ebola outbreak.
A few facts about the 1918 Spanish Flu:
- Caused by an H1N1 virus
- Spread was likely fostered by WWI
- Killed at least 50 million people worldwide
In 6 Souls, a faith healer offers his "skills" to those who fear the pandemic while having his own children inoculated (an anachronism since the influenza vaccine was not available at that time). The townspeople figure out this hypocrisy and punish the faith healer accordingly.
It's important to remember that during the time of the 1918 pandemic the cause of influenza--so named because it was originally thought to be due to the influence of the stars--had not been established. There was no vaccine, no antivirals, and no antibiotics to treat the secondary bacterial infections that were the chief cause of death. I am sure that desperate individuals, like those in the film, unfortunately turned to faith healers who preyed upon the relative ignorance and desperation of the world at that time.
To me the pathbreaking nature of the germ theory stems from its ability to provide a rational, natural, and causal explanation for illness, sweeping away any appeal to the mystical and cutting off faith healers at the root. Even today, let alone in 1918, there are pockets of the population where the germ theory has not penetrated fully into the populace as evidenced by those who forego vaccination and the practitioners of Christian Science who eschew antibiotics.