What Glasseye wrote is true. I read about that myself. Hospitals were overwhelmed so they set up field hospitals. The people in the field hospitals fared far better than the patients indoors. Recovered at a much higher percentage and at a faster rate.
I know all about the Spanish Flu. My son went through an illness with symptoms like COVID-19. He went through all the cytokine storm issues. He has spent nearly 300 days in the hospital in the last three years.
It can’t be fixed by sunlight and fresh air. Back then it was probably all they knew how to do.