If you ever labored through Homer’s The Odyssey in a high school literature class, you may recall the disturbing homecoming of the eponymous hero, Odysseus. What you may not remember is that the final scenes of Homer’s epic poem include one of the older records of disinfection practices in the western literary canon. Here’s what happens: Odysseus returns to his kingdom, Ithaca, after an unplanned twenty-year absence to find his palace overrun with suitors attempting to woo his seemingly widowed wife. Seeing these impertinent pretenders to his throne, Odysseus disguises himself as a beggar and ultimately competes against the suitors to win his wife’s hand. He bests the suitors before revealing his true identity, and then executes them and other members of his household who dared to doubt his eventual homecoming. Having completed this bloody retribution, Odysseus calls on his faithful servant, Eurycleia, to help him rid the palace of these suitors’ and traitors’ residue. He says to Eurycleia, “Bring sulphur…to cleanse from pollution, and bring me fire, that I may purge the hall.” Only after doing so does Odysseus give in to the emotion of his much-delayed return.
Homer’s inclusion of these disinfection details demonstrates that although the materials people may use have changed, the desire to purge the unwelcome is a long-standing human inclination that persists today. In this blog post, we will explore how disinfection and disease mitigation practices have changed over time thanks to evolving understanding of germs and their transmission. We will also examine how some advances in disinfection have proven detrimental, and how we can offset that detriment with layered approaches to infection prevention that don’t require Odysseus’ fire and sulphur methodology to achieve lasting and cleansing results.
Early Understanding of Disease Transmission
While Homer is believed to have composed The Odyssey sometime in the 8th century BCE, it was not until many centuries later that the beginnings of germ theory (and the need for germ management) would creep into western scientific thought. Hippocrates, who lived c. 460-377 BCE, believed that bad air was equivalent to pestilence. Greek physician, surgeon, and philosopher Galen advanced this thinking during his lifetime (c. 130-210 CE) by suggesting that “seeds of disease” could corrupt air.
This idea of bad air or “mala aria” (the origins of the disease name “malaria”) remained popular through the Middle Ages and came to be known as miasmas – “poisonous emanations, from putrefying carcasses, rotting vegetation or molds, and invisible dust particles inside dwellings.” When the Black Death or bubonic plague ravaged Europe and Asia in the mid-1300s, the disease-causing bacteria, Yersinia pestis, acted so quickly and was so contagious that unwitting disease hosts would go to bed healthy and succumb before morning. While people did not fully comprehend how the disease was able to spread so quickly, one doctor during the Black Death era posited, “Instantaneous death occurs when the aerial spirit escaping from the eyes of the sick man strikes the healthy person standing near and looking at the sick.” Today, we know that the medieval bubonic plague was transmitted through the air (rather than the “aerial spirits” of the dying) and through the bites of infected fleas and rats.
Eventually, officials in the Italian port city Ragusa instituted a practice to control the plague’s spread. They required arriving sailors to remain in isolation on their ships for 30 days (a trentino) or for 40 days (a quaranta) – the origins of what we now know as quarantine. This Venetian law combined with increasing sanitation and public health practices helped bring the Black Death to heel: although the bubonic plague still exists today, only about 1,000-2,000 cases are reported to the WHO annually.
For centuries, quarantine remained a foundational element of disease mitigation strategies. As further contagions and epidemics spread throughout the world, isolation and quarantine remained popular means for managing transmission. These practices remained integral to limiting the spread of other diseases like smallpox, cholera, yellow fever, typhoid fever, and more in later time periods. By the early 20th century, experts considered the battle against infectious diseases over – until influenza emerged during World War I. The Spanish flu pandemic of 1918 killed an estimated 20-50 million people, including roughly 675,000 Americans. Officials in some areas continued to impose quarantines but also added mask mandates and the closure and disinfection of public places like churches, schools, and theaters. They also encouraged people to avoid shaking hands and to stay indoors.
About ten years after the Spanish flu pandemic, Sir Alexander Fleming discovered penicillin in 1928. This discovery ushered in the beginning of “the antibiotic revolution” or “the antibiotic era.”
As the leading causes of death in developed countries shifted from communicable to non-communicable diseases, public health and medical professionals shifted their attention to identifying and fighting pathogens on only two of three vectors of transmission. They focused on ways to mitigate spread via human-to-human and surface contact but neglected to consider the airborne “seeds of disease” and mala aria that had fascinated their predecessors in earlier centuries.
The Modernization of Disease Mitigation and Disinfection
One positive outcome of the Spanish flu pandemic was a significant improvement to public health efforts worldwide. Strategies like health education, isolation, sanitation or disinfection, and surveillance continue to inform epidemiological practices today. When paired with antibiotics, these practices create a layered approach to addressing the ongoing challenges of bacterial and viral epidemics. However, antibiotics alone are not a pandemic panacea. Public health education must continue to focus on appropriate antibiotic use and while also encouraging other infection prevention measures via personal and environmental hygiene practices.
While personal hygiene practices such as hand-washing and mask-wearing may be very familiar to us, environmental hygiene practices often get overlooked. Nevertheless, it is a critically important component of any mitigation strategy. Surface disinfection is one of the most common environmental hygiene practices. Chemicals used for this disinfection are most often quaternary ammonium compounds (QACs or quats). Early in the twentieth century, researchers Walter Jacobs and Michael Heidelberger of the Rockefeller Institute worked with chemicals that were the products of ammonia and formaldehyde and could become germicidal or selectively toxic (or what they called bacteriocidogenic). However, due to pressure they received from their institution to focus on polio treatments, Jacobs and Heidelberger did not pursue their discoveries further.
When Gerhard Domagk took up Jacobs and Heidelberger’s work again in the 1930s, he was working under different conditions that encouraged his experimentation. Domagk was in the employ of a large chemical company looking to profit from chemical discovery, while Jacobs and Heidelberger had been working within an academic institution. The compound Domagk created, benzyldimethyldodecylammonium chloride, became known commercially as “Zephirol” and was introduced as a sterilizing agent for hands and instruments. The advent of Zephirol led to many other chemical companies exploring the commercial applications of QACs, which were increasingly called “surface active agents.”
This industry-wide exploration yielded the creation of benzalkonium chloride, which is still used in products ranging from cosmetics to wet wipes to hand and surface sanitizers. Today, the U.S. is the largest producer of chemicals in the world. Yahoo! reports that 96% of manufactured goods rely on chemicals, with 25% of the U.S. GDP supported by the chemicals industry. Major chemical manufacturers in the U.S. include Dow, LyondellBasell, Linde, and DuPont. These manufacturers have made their chemical products indispensable to other sectors like consumer goods, agriculture, manufacturing, computing, telecommunications, and construction. In 2019 and 2020 alone, major U.S. chemical manufacturers spent over $61 million on lobbying efforts for per- and polyfluoroalkyl substances (PFAS), which are “persistent, highly mobile and potentially toxic compounds.” These compounds are used in consumer products ranging from water-resistant clothing to cleaning products.
The Chemicals Industry and Chemical Disinfection Today
Today’s disinfectants draw from the work of Jacobs, Heidelberger, and Domagk in that they use chlorine, hydrogen peroxide, phenols, and QACs. More than 13,000 chemical companies in the U.S. produce over 70,000 products at 11,114 chemical manufacturing facilities throughout the country. 34% of those facilities are owned and operated by smaller businesses employing fewer than 500 people. Between these smaller facilities and their larger counterparts, chemical distributors in the U.S. deliver over 9 tons of chemical products every 8.4 seconds.
For the general consumer, chemicals most often factor into their lives through consumer products like detergents, soaps, personal care products, cosmetics, and even paints. During the first 6 months of the COVID pandemic, many of these subcategories saw dramatic increases in spending. Hand sanitizer spending increased by 838%; bar and liquid soap spending increased by 65%; antiseptics & disinfectants spending increased by 61%; household cleaning spending increased by 62%; and bleach spending increased by 43%.
Most of the products purchased through this increased spending were wipes, sprays, and other surface-focused disinfectants, which have varying degrees of efficacy when used around the home. As The New York Times noted in an article from October 2020, “Disinfectant wipes and spray cleaners have different instructions on their labels for how long a cleaner should stay on a surface to effectively kill germs, ranging from 30 seconds to four minutes or even as long as 10 minutes. What’s more, some labels recommend cleaning before using a disinfectant . . . You probably need to let your disinfectant stay on the surface you’re cleaning for far longer than you think.”
Unfortunately, one of the inherent issues with these products is that this “dwell time” on surfaces can prove hazardous to users’ health. The American Lung Association (ALA) explains, “Many cleaning supplies or household products can irritate the eyes or throat, or cause headaches and other health problems, including cancer. Some products release dangerous chemicals, including volatile organic compounds (VOCs). Other harmful ingredients include ammonia and bleach. Even natural fragrances such as citrus can react to produce dangerous pollutants indoors.” According to the ALA, these dangerous reactions can create formaldehyde, ozone gas, and fine particles, all of which can be life-threatening, inflicting damage on key organ systems like the lungs. Of the ~1.6 million deaths due to chemicals recorded by the World Health Organization (WHO) in 2016, over 47% were due to cardiovascular- or lung-related issues, while 26% were due to cancers.
Given the risks and hazards associated with chemicals, the U.S. government closely regulates this industry. Federal agencies like the Department of Labor Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA) oversee the manufacturing, storage, processing, transportation, and use of chemicals in both the public and private sectors. This oversight of common household products used to disinfect surfaces has been particularly relevant during the COVID pandemic. For liquid and dilutable liquid disinfectants used on hard surfaces, the EPA focuses on “contact time.” Using the Association of official Analytical Chemists (AOAC) Use-Dilution Method, the EPA tests these products’ efficacy by “immersing stainless steel carriers in bacteria (e.g. Staphylococcus aureus), treating them with the disinfectant for a prescribed time, and then placing the carriers in growth media to determine if there are any surviving bacteria. With this test, all microbes on a carrier (e.g., ≥1,000,000 S. aureus on a stainless steel carrier) must be inactivated to result in a negative carrier.”
For towelettes or wipes, the EPA uses a modification of the AOAC’s Germicidal Spray Products Test. For this test, the test organism is applied to a glass surface before the disinfecting wipe or towelette is used on that surface. Following towelette or wipe contact (for 1-2 minutes), “the carrier (i.e., glass slides) is placed in the growth medium for 48 hours to determine if all of the test organisms (e.g., at least 105 S. aureus or Pseudomonas aeruginosa) have been inactivated. During the contact time, the liquid delivered on the glass surface by the wipe is open to drying.” Consequently, the treatment time for the wipe disinfectant includes the wet time plus physical removal of microorganisms by wiping as well as the drying time. To pass the test, the wiped surface must show no detectable growth.
Learning from Chemicals and COVID for Future Success
The fine print (“contact time” or “dwell time”) of chemical disinfection combined with the potentially hazardous side effects (like ozone exposure) demonstrate some of the shortcomings of this disinfection method. In the context of our current pandemic, it is worth noting that when using wipes and sprays, the time required to kill coronavirus can last anywhere from four to ten minutes. That also means four to ten minutes of potentially harmful chemical exposure for anyone in the vicinity of the surface being cleaned.
A further shortcoming of chemical disinfection is that it fails to address and even exacerbates other impacts to health, like air quality. Ongoing public health and household-level efforts to mitigate risk through disinfection need to address all vectors of transmission to be effective. Beyond surfaces, those vectors include human-to-human contact and airborne communicability. The good news is that we have come a long way since Odyssesus relied on sulphur and fire and our medieval forebears relied on quarantine alone to stop the spread of pathogens. Advances in disease management through antibiotics and through a greater understanding of transmission have coincided with advances in understanding how to harness other technologies, like UV light, for its germicidal properties on both air and surfaces.
While Gerhard Domagk was tinkering with QACs in Germany in the 1930s, some of his scientific colleagues in the U.S. were looking at non-chemical means of disinfection. W.F. Wells and M.G. Fair demonstrated in 1935 that ultraviolet germicidal irradiation (UVGI) could inactivate airborne microorganisms, and they went on to demonstrate that upper-room UVGI was able to prevent the spread of measles in suburban Philadelphia schools. These discoveries served as a reminder of what Wells and Fair’s ancient predecessors had suspected: that the “seeds of disease,” as Galen put it, could be sown via the air.
The journey to understand and manage disease has proven a significant and centuries’ long endeavor complete with twists, turns, and detours similar to the journey Odysseus himself took. And just like Odysseus’ lengthy journey, ongoing and holistic infection prevention efforts, particularly when combined with UV disinfection, can prove truly epic in scope. Sustainable disinfection practices layered with transmission mitigation across human-to-human, surface, and airborne vectors will yield better outcomes and a healthier world where mala aria and the “seeds of disease” remain where they belong: in the ancient past.
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