key: cord-0894526-wef8nv7e authors: Li, Yuguo; Nazaroff, William W.; Bahnfleth, William; Wargocki, Pawel; Zhang, Yinping title: The COVID‐19 pandemic is a global indoor air crisis that should lead to change: A message commemorating 30 years of Indoor Air date: 2021-10-18 journal: Indoor Air DOI: 10.1111/ina.12928 sha: 37ecae77f0c159538929c912c3487b32d45e7800 doc_id: 894526 cord_uid: wef8nv7e nan died, 1 and the associated disruption caused a 7% economic loss during 2020. 2 Global vaccination is not proceeding rapidly enough to eliminate the virus as it continues mutating into variants of concern. With its unlikely elimination, SARS-CoV-2 will remain an ongoing challenge together with other endemic infections such as influenza. Many reflections about the pandemic have been written, but one major topic seems to have been ignored: What could have been done to prevent the transmission of SARS-CoV-2? No transmission means no pandemic. In 1969, the American author Michael Crichton wrote in his novel The Andromeda Strain about the effort to contain a deadly extraterrestial pathogen, "A crisis is the sum of intuition and blind spots, a blend of facts noted and facts ignored." What are the blind spots and the facts ignored in the COVID-19 pandemic? The infectious disease transmission concepts of airborne, droplet, fomite, and contact routes have remained nearly unchanged since the sixteenth century even though the underlying science developed rapidly starting in the early twentieth century. 3 The terminology is confusing for the public and even scientists are challenged to communicate clearly across disciplines. In some relevant academic workshops we have attended, participants spent disproportionate time attempting to reconcile what is understood to be airborne transmission. The airborne route is easily conflated with long-distance transmission, which is inaccurately perceived to be fearful, dangerous, and very difficult to control. Short-range airborne transmission is often confused with the large droplet route. In a recent Indoor Air editorial, 3 a set of new terms was proposed: aerosol inhalation, droplet (drop) spray, and surface touch. With these three transmission concepts, the associated interventions should be easy to identify-minimize inhalation of infectious agents, avoid contact via drop deposition, and keep surfaces/hands clean. A similar set of terms was recently adopted by US CDC, 4 that is, inhalation, deposition, and touching. WHO 5 and US CDC 4 also have finally accepted that short-range inhalation predominates the transmission of SARS-CoV-2, more than a year into the pandemic. The underlying axiomatic statement in the above analysis is that COVID-19 infection is mainly due to respiratory droplets. During heavy physical activities, an infectious person would exhale more air and produce higher shear stress at the epithelial surface, consequently releasing more infectious droplets. During physical exertion, a susceptible individual also inhales more. The net effect for infection transmission risk is a double multiplier. In an office setting, by contrast, both the infectious and the susceptible breathe at lower rates. Assume in the case of an office, an appropriate ventilation rate is 10 L/s per person. Then, in a gym, the infectious would exhale more, say by 5×, and the susceptible would also inhale more, also by 5×. The exposure rate to exhalations could likely be 25× the office value, and a rational ventilation requirement might therefore also 25× the We may cite two relevant major environmental revolutions during the past few centuries. The first is the sanitary revolution. Rapid industrialization and urbanization in the 18th and 19th century led to spread of infectious diseases in major cities in Europe and United States. This public health crisis was followed by major efforts in revolutionizing wastewater treatment and discharge, water quality improvements, and personal hygiene. Building regulations were introduced with mandatory requirements. Probably due to the defeat of the old miasma hypothesis, some progress was also made toward air hygiene. Second, the deadly Donora smog of 1948 and London fog crisis of the 1950s initiated a new urban air revolution. Strict governmental regulations were adopted, with a lot of new research efforts. Urban air quality in major industrialized countries improved significantly. In China, the city haze or PM2.5 crisis in the early 2010s also had a similar impact, with government acting strongly and urban air quality significantly improving. Government regulation and research are necessary but not sufficient; the economy and technology also need to be sufficiently good to fund required infrastructure improvements. We learned scientifically about air and water in the 18th century, and about germs in the 19th century. Human mortality attributable to infectious diseases has declined markedly following the sanitary revolution. But, importantly, respiratory infections still have broad adverse impacts in both rich and poor countries. 11 Two explanations are suggested, both probably related to indoor air. The first is the increasing inequality between the poor and rich. The health inequality is clearly seen in high COVID-19 infection rates and mortality among Blacks, Hispanics, and Native Americans in the United States, 12 and in the ongoing COVID-19 human disaster in India. 13 Poor housing and crowding are major issues. The second feature is our ability to construct more airtight buildings. Rich countries may have better healthcare facilities, but their indoor air might not be the best. Unlike water, air is everywhere. Ever since we have built tighter buildings, good air is no longer always pres- worldwide. This is also an age of carbon neutral and sustainability. Health is an essential element of sustainability, and developing carbon neutral indoor air technologies is essential. Access to healthy indoor air is a basic human right. 15 It goes with healthy living and sustainable development. The indoor air revolution of the 21st century will not come if we do not act. New research is needed, but more importantly, new regulations, public education champaigns, and new human air hygiene behavior are essential. There is a major difference between handwashing and ventilation. Hand washing may be an individual behavior, but for ventilation, we often have no say in the restaurants we patronize, gyms we visit, and buses we take. Similar to that for water hygiene, voluntary requirements will not be sufficient for indoor air quality, and mandatory regulations should be enacted. An editorial commemorating the 20-year anniversary of Indoor Air included these thoughts 16 : "One might be discouraged about the limited size of our community in relation to the scale of the challenges we face. However, it has always been that great discoveries are made by small and determined groups of explorers." Indoor Air and indoor air scientists have contributed to the scientific understanding of transmission and intervention in the pandemic. However, the COVID-19 crisis suggests that much more must be done. COVID-19 pandemic, indoor air, indoor air crisis, ventilation None of the authors have a conflict of interest. YL involved in writing the original draft, and all authors involved in writing-review and editing. The peer review history for this article is available at https://publo ns.com/publo n/10.1111/ina.12928. Data sharing not applicable to this article as no datasets were generated or analysed during the current study. https://orcid.org/0000-0001-5749-6543 Pawel Wargocki https://orcid.org/0000-0003-3865-3560 World Health Organization WHO Coronavirus (COVID-19) Managing Divergent Recoveries. 2021. Last accessed Basic routes of transmission of respiratory pathogens-A new proposal for transmission categorization based on respiratory spray, inhalation, and touch Scientific brief: SARS-CoV-2 transmission Coronavirus disease (COVID-19): How is it transmitted? 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