What were some things that people in the story Fever 1793 think caused yellow fever?

In
chapter 8, Mr. Carris reads the mayor's orders from a broadsheet newspaper. From these orders we
can infer some of the factors which people in the story think of as possible causes of yellow
fever.

The first order is that everybody "should avoid those that are
infected." The implication here is that people think that yellow fever is contagious via
direct contact with those already infected. This thought is confirmed by the second order, which
states that "The homes of the sick should...