Contingent contagionism was a concept in 19th-century medical writing and epidemiology before the germ theory, used as a qualified way of rejecting the application of the term "contagious disease" for a particular infection.
[1] Contingent contagionism covered a wide range of views between "contagionist", and "anti-contagionist" such as held by supporters of the miasma theory.
Anticontagionists, for example, argued that infection could be at a distance, from a cause that could be sporadic and possible diffused through the air, and taking advantage of "predisposed" individuals.
[7] It has been commented that those involved in public health at this time, successful in bringing down death rates, "often attributed disease causation to levels farther up the causal chain than direct biological mechanisms".
Having mentioned William Pym (contagionist) and Edward Nathaniel Bancroft (anti-contagionist) as extremists, it went on to say (italics in the original) That the yellow fever of the West Indies [...] is rarely contagious, under common circumstances of cleanliness and ventilation, is as well ascertained as any fact in medicine.