On the importance of hygienic measures in the control of airborne infectious diseases

Dear Editors,

Infectious diseases have spread primarily in the form of epidemics throughout the history of mankind and pathogenic microorganisms have long been held responsible for their occurrence. However, pathogenic microorganisms make up only a small portion of the microbiome of humans, animals and plants [1].

In order to understand the role of microorganisms in disease etiology, we have to remember that the environmental conditions in which microorganisms are found play a decisive role in their functioning in relation to the environment, and thus in relation to their hosts, as their specific environment.

In acute infectious diseases, the pathogenic microorganism most commonly stimulates various lytic, primarily proteolytic reactions, through various proteases [2],[3],[4],[5], thus it has a role of catalyst in the pathological process. The role of catalyst is only to accelerate the reaction, it cannot initiate the reaction, nor can it change the equilibrium position of the reaction [6]. Therefore, at least when it comes to the inflammatory process, the so-called biological causes of disease are not the actual causes, but only catalysts of an already existing pathological process, while the real immediate causes are, by their nature, only physical or chemical factors. Hence, the extreme variability of both the location and intensity of pathological processes with the same biological causative agent in different individuals of the same host species. Consequently, the clear designation of most microorganisms that can "cause" the disease as opportunistic pathogens, as opposed to the so-called strict pathogens [7]. However, "strict" pathogens are basically also opportunistic, conditional pathogens, in the sense that they need appropriate environmental conditions in order to manifest their pathogenicity. However, they differ from conditional pathogens only in that they cannot survive in different conditions, due to their poor adaptability to changes in their environment. Thus, pathogenicity and virulence of microorganisms are not their inherent and invariable properties, they are merely the result of pathogenicity of inanimate environmental factors, which act on the host, and which usually remain out of the focus of medical research.

“Life’s teacher” – history, offers the answer to the question of key practical significance: how do we prevent the occurrence of infectious diseases? Even before the discovery of infectious agents and specific antimicrobial drugs, many hygienic measures were sufficient to reduce most infectious diseases, such as cholera and plague in earlier centuries, which broke out in the form of epidemics that decimated the human population. These infections were reduced to a negligible incidence in the environments where such measures were applied. In particular, the introduction of the sewage system and the regular removal of solid, especially organic waste from populated areas have contributed to the past epidemics of cholera and plague falling into oblivion. Thus, for example, plague was successfully controlled by direct deratization and disinsection measures [8], and regular solid waste removal certainly contributed to the control of vectors of both plague and other dangerous infectious diseases, by removing the substrate necessary for the preservation and the multiplication of the appropriate vectors. The control over cholera was established by the introduction of a hygienically safe supply of drinking water [9] and, in Serbia, in 1915, a terrible epidemic of spotted fever was eliminated by developing and systematically using the so-called Serbian barrel, without significant contribution of any specific antimicrobial or immunostimulating drugs [10].

So far, the community has made significant strides in the improvement of hygienic standards of personal and family housing, processes in food production and animal husbandry, the safe disposal of municipal solid and liquid waste, as well as in the domain of the hygiene of business facilities and processes. However, one important segment of hygiene practice has remained quite undeveloped and neglected to this day, and that is the care for the hygiene of the atmosphere, primarily the atmosphere of human settlements. Today, the atmosphere is constantly and systematically polluted with specific gases, vapors as well as particles, including radioactive, toxic and infectious particles. The direct result of this state of development of hygiene practice is that, nowadays, the only type of epidemic affecting the general population are epidemics of diseases that spread through the atmosphere, i.e., epidemics of respiratory (airborne) diseases. While the majority of the public sees the specific vaccine as the only hope of salvation from the current respiratory COVID-19 pandemic, very few understand that the vaccine might be only a temporary solution to the problem. For example, some medical professionals have recently publicly expressed the opinion that, even after the possible elimination of COVID-19 solely by means of vaccination, subsequently, a COVID-22, -23 or -24, may follow, and so on, indefinitely. This prediction can be deduced directly from the lessons of history, including those mentioned above. For example, what would happen if, at this day and age, we fought plague and cholera only with vaccines and antibiotics, and on the other hand continued to live in settlements where human and animal excrements and solid organic waste accumulated continuously? The answer is that in that case we could certainly expect a constant emergence of new, more resistant strains of pathogenic bacteria or other pathogens and the reappearance of diseases in altered forms, because vaccines and antibiotics alone would not be sufficient to nullify the favorable conditions for disease persistence and development.

For the purpose of achieving permanent control over the epidemics of airborne diseases, there is a need to introduce permanent and systematic measures to maintain the hygiene of the atmosphere of human settlements. For a start, we should focus on removing particle pollution, as we mustn’t forget that viruses and bacteria causing respiratory diseases are, in their physical form, particles. However, what would be more important than physically removing infectious agents from the atmosphere is the removal of toxic particles from the atmosphere, which themselves cause a pathological process, which is then merely accelerated by microorganisms. Regarding harmful ingredients in the atmosphere of modern cities, a group of experts of the US Environmental Protection Agency concluded that the current PM2.5 standards are insufficient to protect public health, and this conclusion was based on substantial and comprehensive evidence from epidemiologic studies, toxicologic studies on animals, and controlled human exposure studies [11].

While public response to particulate matter toxicity, as an obscure risk that mainly has consequences in the long term, may be delayed for some time, recent research indicates that toxic particles in the atmosphere play an essential role in spreading the current COVID-19 pandemic, and that therefore their systematic removal is a high public health priority. Thus, for example, an undeniable and high correlation was found between the concentration of PM2.5 particles in the air, on one hand, and both incidence and mortality from COVID-19, on the other [12],[13],[14],[15].

The largest areas where particles of organic and inorganic origin are deposited are open public spaces, streets, squares, parks, etc. The deposited particles are washed away by natural precipitation and drained to lower areas, so that the settlements on elevated terrain are at an advantage, in that respect, over the settlements located on lower terrain. However, in dry periods, regardless of the ground surface configuration, particles remain on the ground and are then constantly lifted into the atmosphere by air flow. In the past, public utility companies occasionally washed the streets, primarily roads, which is obviously a rare practice nowadays. Today, it is visible to the naked eye that dust is constantly being generated in larger settlements, both in traffic, as well as during the activities of construction companies, during processes of burning fuel in heating plants and companies, as well as by burning solid materials in houses, private and public areas. Therefore, there is a need for regular (e.g., every night after a dry day with no strong wind) washing of public areas. It should preferably be done with chlorinated or ozonated water so as to inactivate infectious dust, as well as to detoxify toxic organic particles [16],[17]. This certainly implies a permanent increase in the extent of regular work as well as the standardization of performance quality of public utility companies, or companies whose task would be based on public-private partnership, with permanent public control of the performance quality of these companies.

In addition to the regular cleaning of public areas from particulate matter, it is necessary to compel major particle generators (construction companies, heating plants, vehicles) to apply all available measures for retaining particles at their source, and safely disposing of them. Due attention should also be paid to regular disinfection of closed public spaces (public administration buildings, hospitals, schools, cultural institutions, etc.). As a current practical option, there is a procedure of night ozonation of rooms with arc-based ozonizers [18] or UV lamps of 185 nm [19]. These measures should certainly be carefully planned and prepared for implementation, and, upon verification of their effect at sentinel sites, they should cease to be seen as temporary measures, but rather measures that are as permanent and sustainable as personal hygiene measures, water supply, and sewage system and solid waste disposal.

Health professionals should certainly take every possible step to advocate and help to introduce these and other necessary hygiene measures aimed at protecting the air we breathe and defending against airborne infections, and thus contribute in the best way to the further improvement of public health.