Infection is caused by ….
I came across this Rudolf Steiner lecture recently published in “The Presence of the Dead” Chapter 3. Awakening Spiritual Thoughts given in 5 May 1914. https://rsarchive.org/Lectures/19140505p01.html
At the core of Steiner’s ideas is the effect of fear of infection.
“However, the important point we want to make today is that germs can become dangerous only if they are allowed to flourish. Germs should not be allowed to flourish. Even materialists will agree with this statement, but they will no longer agree with us if we proceed further and, from the standpoint of proper spiritual science, speak about the most favorable conditions for germs. Germs flourish most intensively when we take nothing but materialistic thoughts into sleep with us. There is no better way to encourage them to flourish than to enter sleep with only materialistic ideas, and then to work from the spiritual world with the ego and the astral body on those organs that are not part of the blood and the nervous system. The only other method that is just as good is to live in the center of an epidemic or endemic illness and to think of nothing but the sickness all around, filled only with a fear of getting sick. That would be equally effective. If fear of the illness is the only thing created in such a place and one goes to sleep at night with that thought, it produces afterimages, Imaginations impregnated with fear. That is a good method of cultivating and nurturing germs. If this fear can be reduced even a little by, for example, active love and, while tending the sick, forgetting for a time that one might also be infected, the conditions are less favorable for the germs.”