Some people believed just something about "bad air" (origin of word "malaria" is mala aria from medieval Italian).
This article in 1936 notes that no real way to show until recently. Hence, they wrote this article.
Mr. Wells passed away, having passed the torch to his protege Riley who continued to work on air matters.
I am still trying to locate information about his wife Dr. Wells, but she certianly wrote her own articles about measles,etc.
I checked his book just now and Chapin was the Superintendent of Health for Providence Rhode Island. But no mention of his credentials, so my comment might not be correct. I'll check when have time.
He is also a fascinating read. Pioneered that pathogens live and transmit between hosts instead of throughout the environment. So can study chain of transmission. His book at Internet Archive.
His tech caught tuberculosis.
Answers that Wells' wife had died previously
atsjournals.org/doi/10.1164/aj…