Research shows that outdoor air is a natural disinfectant. Fresh air can kill the flu virus and other harmful germs. Equally, sunlight is germicidal and there is now evidence it can kill the flu virus.
Open-air therapy, as it was known, was widely used on casualties from the Western Front. And it became the treatment of choice for another common and often deadly respiratory infection of the time; tuberculosis. Patients were put outside in their beds to breathe fresh outdoor air. Or they were nursed in cross-ventilated wards with the windows open day and night. The open-air regimen remained popular until antibiotics replaced it in the 1950s.
Patients treated outdoors were less likely to be exposed to the infectious germs that are often present in conventional hospital wards. They were breathing clean air in what must have been a largely sterile environment. We know this because, in the 1960s, Ministry of Defence scientists proved that fresh air is a natural disinfectant. Something in it, which they called the Open Air Factor, is far more harmful to airborne bacteria — and the influenza virus — than indoor air. They couldn’t identify exactly what the Open Air Factor is. But they found it was effective both at night and during the daytime.