In a recent study published in Indoor Air, researchers looked broadly for the origins of resistance to recognition of airborne transmission during the coronavirus disease 2019 (COVID-19) pandemic by major public health organizations, including the ‘World Health Organization (WHO) and the United States. State Centers for Disease Control and Prevention (US-CDC).
Study: What were the historical reasons for resistance to acknowledging airborne transmission during the COVID-19 pandemic? Image credit: Evgenia.B/Shutterstock
background
Early acceptance of the evidence for airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) would have reduced the effort, time and money wasted on adherence to the use of interventions, such as surface disinfection and Plexiglas side barriers, were ineffective in containing COVID-19. Subsequently, the general public would have focused on ventilation, filtration and the use of masks, with a better fit and filters, even indoors where social distancing was feasible.
In part, WHO and CDC hesitated to embrace airborne transmission of SARS-CoV-2 even in the face of evidence because of a conceptual error that occurred more than a century ago and was embedded in the fields of public health, epidemiology and infection prevention. .
About the study
In the present study, researchers surveyed historical theories of disease transmission from antiquity to the present day and relevant literature in PubMed, Google Scholar, and Web of Science to highlight key trends that led to the adoption of the theory of disease transmission. In addition, they consulted with experts to identify other relevant articles on these topics. In addition, the team tracked backward for references in these articles and tracked the source forward in Google Scholar to see which other sources cited it through forward tracking.
In addition, the researchers used hermeneutic methods to develop a narrative of the identified literature and show how scientists originally conceptualized the transmission of some diseases; and what empirical evidence led scientists to revise these models. They refined their interpretation by looking for disconfirming studies that challenged prevailing disease models and hypotheses.
Brief history of disease transmission
The Hippocratic writings of ancient Greece first proposed that miasmas (or bad air) were transmitted through the air to cause mass epidemics. Marcus Terentius Varro, a Roman scholar, proposed that swamps bred tiny creatures that floated in the air and entered the human body through the mouth and nose to cause serious disease. Regardless of the mode of transmission (bad air or tiny creatures), historically, airborne infections were generally not considered contagious and transmissible from human to human. Indeed, establishing modes of transmission was difficult for scientific and sociological reasons. Also, without microscopes and a germ theory of disease, it was difficult to distinguish between various possible modes of transmission.
Girolamo Fracastoro, in 1546, formulated the theory of the transmission of diseases from man to man. He proposed that the seeds of ‘contagion’ or ‘seminaria’ that cause disease are transmitted through three modes: direct, indirect and distance. The contagion, which I thought was a chemical, was strongest at a distance. About 50 years later, Hans and Zacharias Janssen invented the microscope in 1590, which led to the discovery of microorganisms, the real contagions.
During the London cholera epidemic of 1854, John Snow noticed how cases had clustered in a particular London district. He convinced the local authorities to remove the handle of the Broad Street water pump to stop the epidemic. Ignaz Semmelweis, another pioneer of disease transmission, showed that hand washing reduced deaths from infant fever in a maternity clinic.
In 1861, Pasteur conducted experiments to demonstrate the presence of viable microorganisms in the air. However, it was not until the late 1880s that the miasma theory declined in popularity. The discovery of microorganisms as agents of disease did not eliminate the challenge of definitively determining how they were transmitted between humans.
In another example of the complexities involved in inferring modes of disease transmission, most experts believed that tuberculosis was transmitted when dust from dried sputum that had fallen on the floor or other contaminated objects became airborne. In reality, fresh skin secretions from patients floating in the air caused tuberculosis. Flügge and his collaborators were the first to use the term droplet to refer to fresh air particles of all sizes, including aerosols.
In 1905, microbiologist MH Gordon studied the atmospheric hygiene of the UK House of Commons following an influenza epidemic among members. He successfully investigated the spatial extent of aerosols and droplets containing pathogens. Although there were many more bacterial colonies on the plates near the speaker, cultures were evident on some plates up to 21 meters away. He was unable to make further progress due to the unavailability of better experimental techniques at the time.
Renowned American epidemiologist Charles V. Chapin first conceptualized contact infection, that is, infection that did not come from the environment, but from other humans directly or by proximity. It was the turning point in the history of airborne disease transmission. Chapin conceived of airborne infections as infections from afar, and his unproven ideas and hypotheses were accepted as evidence of droplet transmission. This error remained entrenched for years to come, even at the onset of the COVID-19 pandemic.
The droplet transmission paradigm dominated until the start of the COVID-19 pandemic
Although some public health announcements in China early in the COVID-19 pandemic reported that SARS-CoV-2 was airborne, a paper published in Nature concluded that “the disease could be transmitted by airborne transmission, although we cannot rule out other possible routes.” of transmission”. Despite a lack of evidence supporting modes of transmission of SARS-CoV-2 in droplets or fomites, the WHO concluded that COVID-19 was transmitted by these mechanisms, continuing Chapin’s error.
Aerosol-generating procedures (AGPs) were the only circumstance in which WHO accepted airborne transmission; consequently, WHO did not change this misconception until January 2022. WHO and other public health organizations around the world ignored the airborne mode of transmission of SARS-CoV-2 for almost a year. They remained entrenched in the old gout paradigm and continued to ignore the 70-year delay in recognizing measles and chicken pox as airborne, and that pulmonary tuberculosis was exclusively ‘air and yet less infectious than COVID-19.
Several studies during the COVID-19 pandemic showed that patients produced more aerosols through breathing, speaking and coughing, which required caution, but WHO continued to emphasize AGPs. Accumulating evidence that COVID-19 is a predominantly airborne disease made it clear that it was a logical fallacy to try to control the pandemic only through droplet/fomite measures such as physical distancing, hand washing and the disinfection of surfaces.
The studies published multiple cases of long-range airborne transmission, such as in quarantined hotels. Also, there were cases of COVID-19 in hospitals despite surgical masks and eye protection and among patients sharing a room despite physical barriers. It was only in May 2021 that WHO and CDC partially accepted airborne transmission of SARS-CoV-2. However, as of January 2022, despite acceptance, it did not receive enough publicity and changes in mitigation measures only partially reached most of the world.
The five micron error and its implications
Aerosols or inhalable particles must be smaller than ~100 μm to travel beyond the vicinity of the infected person. Milton first proposed avoiding the ambiguous term droplet and using the terms aerosols for smaller (inhalable) particles. The July 2020 WHO scientific paper on the transmission of COVID-19 repeated a long-standing error in previous guidelines and the scientific literature. They placed the separation between the droplets that fall on the ground at one or two meters and the aerosols that remain in the air at five microns. The correct value is on the order of 100 μm, published by Wells in 1934.
Conclusions
The miasmatic paradigm prevailed for two millennia and weakened only after the discovery that various diseases (eg, cholera, malaria) that had been thought to be airborne were, in fact, by other means and by the acceptance of the germ theory. Chapin then wrote a book that classified the modes of disease transmission, thus bringing germ theory into the study of disease transmission. The success of his unproven theories led to the paradigm of droplet transmission for all respiratory diseases and dismissed airborne transmission as unimportant for disease transmission in the 1930s. Consequently, in the second half of the 20th century, there was great resistance to accepting diseases as airborne.
The COVID-19 pandemic re-popularized the fallacies inherent in the droplet theory, piloting a more objective paradigm for airborne transmission. However, the overwhelming dominance of the Chapin paradigm led to a persistent lack of attention to the details of the physics of airborne transmission and the opinions of experts in aerosol science and occupational medicine. However, it remains puzzling that the five-micron error persisted and was present in the latest WHO scientific report on the transmission of SARS-CoV-2.
The authors of the current review found no reviews (so far) summarizing the evidence supporting droplet transmission, although it is indicated by the WHO as the main mode of transmission of SARS-CoV-2. Fortunately, the intense research and debate associated with the…