An Old Defence Against New Infections: The Open-Air Factor and COVID-19

Abstract

Outdoors, the risks of transmission of COVID-19 and many other respiratory infections are low. Several environmental factors are known to reduce the viability of viruses and other infectious pathogens in the air. They include variations in temperature, relative humidity, solar ultraviolet radiation, and dilution effects. But one agent that reduces the viability of both viruses and bacteria outdoors, the germicidal open-air factor (OAF), has not been properly recognized for decades. This is despite robust evidence that the OAF can influence both the survival of airborne pathogens and the course of infections.The germicidal effects of outdoor air were widely exploited during the late 19th and early 20th centuries. Firstly, in the treatment of tuberculosis patients who underwent 'open-air therapy' in sanatoria; and secondly by military surgeons during the First World War. They used the same open-air regimen in specially designed hospital wards to disinfect and heal severe wounds among injured soldiers. It was also used on influenza patients during the 1918-19 pandemic. Later, in the 1950s, open-air disinfection and treatment of burns were proposed in the event of nuclear warfare. During the 1960s, the OAF briefly returned to prominence when biodefence scientists conducted experiments proving that open air has a potent germicidal effect. When this work ended in the 1970s, interest in the OAF again fell away, and it remains largely ignored.The COVID-19 pandemic has revived interest in understanding the transmission dynamics and survival of viruses in the air. The pandemic has also stimulated research in the science and practice of improved ventilation to control respiratory infections. Such work is incomplete without an appreciation of the inactivation of viruses and other pathogens by the OAF, but this needs further investigation as a matter of urgency. Research to better understand the conditions under which the OAF can be preserved indoors is urgently needed. We need to review building design with better regard to infection control and patient recovery. But we need to act without delay, as there is already sufficient evidence to show that public health generally would improve if more emphasis was placed on increased exposure to outdoor air.

Homelessness, Politics, and Policy: Predicting Spatial Variation in COVID-19 Cases and Deaths

“…This counterintuitive result may reflect the underlying bicoastal pattern of homelessness, which is higher where government intervention, legitimate rules, support for the common welfare, and Democratic partisanship are also greater. Another possibility is that people living on the street actually benefit from the germicidal open-air factor and relatively rare person-to-person COVID-19 transmission outdoors [ 35 , 36 ].…”

Triggering of an Epidemic Outbreak via Long-Range Atmospheric Transport of Bio-Aerosols—Application to a Hypothetical Case for COVID-19

“…The recent COVID-19 pandemic has reactivated the interest in OAF, and a few papers have appeared on this question [71,72]. There are no laboratory results, and they do not offer any further evidence beyond the very few results reported around fifty years ago.…”

Correlation between UV Index, Temperature and Humidity with Respect to Incidence and Severity of COVID 19 in Spain

“…Solar UV radiation reaching earth's surface does not contain UVC, due to its absorption by atmospheric oxygen (wavelengths below 200 nm) and the stratospheric ozone layer (wavelengths of 200-290 nm). However, solar UVB as well as UVA radiation reaching the earth's surface has been proposed to be an environmental determinant shaping COVID-19 transmission at the seasonal timescale [10] and has been reported to be clearly negatively correlated with infection levels and mortality of patients [11][12][13][14]. Moreover, wavelengths other than solar UVB have been demonstrated to be involved in COVID-19 inactivation.…”

“…Temperature seems also to be important for SARS-CoV-2, which has been reported to be highly stable at 4 • C but sensitive to heat [11]. Several studies suggest that environmental conditions may have affected the COVID-19 pandemic, although the results are controversial.…”