@redleg – I think you are misinformed.
One hundred years ago germ theory was not far past its infancy. Although Semmelweis (1818-1865) had pioneered antiseptic procedures introducing handwashing to medicine, it was not until the 1870s that Louis Pasteur (1822–1895) established the foundation for germ theory, showing that microorganisms were the cause of disease, bolstered by the studies of Joseph Lister (1827-1912) who expanded upon limiting infection in wounds by use of antiseptics.
These scientific practices and theories were not universally understood by the time of the 1918 epidemic, and more primitive remedies and treatments were still in use. Although I can’t address how the poskim ruled at the time, my understanding of public health practices of that time allow me to assert that even civil health authorities did not have a handle on the disease. Soldiers had the flu in early 1918 yet were sent to Europe. They carried it with them. Further, witness the ravages caused by a mass gathering in Philadelphia during the September 28, 1918 Liberty Loans parade. Military deaths were written off as being “the old-fashioned grippe” by Philadelphia’s director of public health!
A good reference article is Philadelphia Threw a WWI Parade That Gave Thousands of Onlookers the Flu
sorry, smithsonian link removed
In 1918, my Bubba and Zayda in Russia didn’t have running water let alone modern communications. You overestimate how well news and scientific information spread 100 years ago.