Indoor air: A short history of holistic and reductionistic approaches.
The indoor air science community is familiar with both the research and community hygiene efforts of Max Joseph von Pettenkofer (1818-1902). Among his many great achievements and contributions to the science, policy, and practice of hygiene,1 Pettenkofer first observed and demonstrated how carbon dioxide could be used as the main indicator of indoor air quality when determining the required ventilation rate in a building. Today, this indicator remains in use as industry standard practice. To honor the pioneering contributions of Pettenkofer to building ventilation, the International Society of Indoor Air Quality and Climate (ISIAQ) established the Pettenkofer Gold Medal in the late 1990s. This medal has been awarded at each of the Indoor Air conferences since 1999, in recognition of an individual's outstanding work toward advancing the indoor air sciences.2 One of the most frequently told stories of Pettenkofer is a germ swallowing drama. Pettenkofer did not believe in the germ theory set forth by Robert Koch (1843-1910), having developed his own soil miasma theory of cholera. To prove his theory, he requested a sample of Vibrio cholerae bacteria from Koch's team and, on October 7, 1892, at the age of 74, he swallowed an estimated 109 bacteria in front of an audience after emptying and neutralizing his stomach. Remarkably, Pettenkofer suffered only mild symptoms after swallowing this pathogenic solution. Earlier writers suggested that he was lucky and have offered various unverifiable explanations.3 Why would such a leading pioneer and thinker in the field of hygiene have missed the new era of the successful germ theory of disease? Locher 1 summarized that “Pettenkofer postulated the existence of a cholera germ that bred in the intestine and spread by means of human excrement, but that was not contagious. This germ, incapable of triggering an epidemic by itself, had to coincide with certain putrescent materials existing in the soil to produce a highly infectious agent that caused cholera.” In other words, although Pettenkofer did not deny the existence of the microbe, he denied its direct infectivity. Accordingly, the soil miasma theory was a result of a conceptual error even though it was developed following extensive epidemiological investigations, according to Evans.3 But why did Pettenkofer feel the need to perform a dramatic and potentially fatal act such as swallowing a lethal pathogen? On this topic, he said, “I would have died in the service of science like a soldier on the field of honor”.3 This leads to the following question: What are the major differences between his theory, which he defended so passionately, and that of Robert Koch? When some of us first began to learn about the science and engineering of ventilation, we may have read the excellent review written by Jan Sundell, a former editor-in-chief of theIndoor Air journal. Sundell wrote that, “indoor air was believed to be a major environmental factor for more than a hundred years, from the start of the hygienic revolution, around 1850, until outdoor environmental issues entered the scene, and became dominant around 1960”.4 A new researcher in the field of indoor air sciences might wonder why society experienced a sudden shift then in focus away from such an important element as indoor air. What were the major issues with indoor air in Europe around 1850 that are not with us today? This question can be answered by reference to the miasma theory and also to recognizing the role of crowding. People died at much younger ages in the 18th and 19th centuries than at present, and, accordingly, both physicians and the community focused strongly on public health. At that time, foul or polluted air was suspected to spread disease among people, and lethal diseases were given priority. In light of the hypothesis that disease is spread by corrupted air and pollution, improved sanitation standards in all buildings, streets, and cities, which included improving the indoor air quality via better ventilation, comprised one of the major efforts to escape from disease. Indoor air hygiene efforts in Western countries in the 19th century also coincided with the need for improved sanitation in urban areas and for reducing the incidence of disease as urban populations grew. According to Ekici,5 “Starting in the 1830s and 1840s, a growing number of middle-class reformers in Germany, Britain, France, and the United States raised public awareness of health issues. Their agenda included all aspects of urban design, from sewers and water supplies to street layouts and the construction of healthy buildings…When hygiene first emerged as a new science, it was closely associated with physiology. The physiology of the human body dominated nineteenth-century scientific thought, providing visual theoretical models for the laws of life and mind.” Tuberculosis, smallpox, and cholera were probably among the top microbial killers of the 19th century. In 1864, Pasteur demonstrated that the theory of spontaneous generation was incorrect. Specifically, he showed that microscopic life could only originate from other life and could not be generated from inorganic substances or non-living organic debris. This discovery was a major scientific milestone. In the late 19th century, some laboratories began to culture pathogens specifically responsible for different diseases. For example, Robert Koch identified the causal bacterium of tuberculosis in 1882 andVibrio cholera, the causative agent for cholera, in 1883. Humans now understood that each infectious disease resulted from a particular microbe. This discovery was powerful, as it enabled the identification of any location, person, or item harboring a particular infectious microbe as a potential health hazard and target for intervention. This discovery ushered in a new era of targeted interventions for preventing infectious diseases in humans. As described by Barnes,6 “the new public health” since the 1880s “narrowed the range of factors identified as potential causes of disease. Just as clearly, it broadened the range of official interventions that could be brought to bear on the prevention of infectious disease, as well as the laws, regulations, and institutions that could facilitate those interventions.” The old miasma theory was concerned with possible associations between environmental factors (eg, polluted air) and diseases, whereas the new germ theory addressed the causation of disease by a particular pathogen. Accordingly, once the specific pathogen was well controlled, the disease spread could be stopped. It was difficult to believe that a highly intelligent person such as Pettenkofer could not appreciate such a simple but powerful idea. Therefore, one might ask: Was he preoccupied with a more powerful idea? The development of germ theory was indeed rapid in the late 19th century, and scientists were excited about its potential applications for disease control. People quickly realized that germs were present not only invisibly in the air but also, importantly, to a greater extent in some environments more than others. In this context, indoor air quality became important. In the late 1870s and early 1880s, researchers at the Montsouris Observatory measured the airborne microbe concentrations at various locations in Paris (6, Page 42). Since then, humans have not only identified the microbes, but have also determined how to count these organisms. In Paris, indoor air from hospitals was found to harbor 100,000 microbes per cubic meter, compared to 10,000 and 1000 per cubic meter in outdoor air from the city center and from a park on the southern edge of the city, respectively (6, Page 129). Chauvel thus estimated that a tenth of the city air microbes detected in Paris were derived from the countryside (6, Page 130). Chauvel also reported that the incidence rates of some diseases, such as typhoid fever, smallpox, and measles, “followed almost exactly with one week's lag” behind the relative numbers of detected bacteria, “so that a rise in the latter announces an increase in these diseases, just as the falling barometer announces bad weather.” However, Chauvel did not provide a reference for the location or methodology related to this finding. Interestingly, people in France learned that ocean and mountain air were microscopically cleanest, whereas hospital air was dirtiest. Scientists at that time even recognized that wind could carry and transport dusts and microbes over long distances (the exact distances were not specified). Further, Marie-Davy (6, Page 136) reported in 1882 that not all microbes were equally dangerous. “By what special grace…would these microbes all be harmless to us…If these microbes were all inoffensive, why would we see, every season, variations in mortality by [infectious] disease follow in such a…regular manner the variations of the total number of microbes contained in the air that we breathe?” Pasteur and his colleagues concurred by stating that “not everything that stinks kills, and not everything that kills stinks” (6, Page 47). The miasma theory appeared to be related to early developments in chemistry and microbiology. Pringle7 wrote: “I conceive that the miasma or septic ferment (consisting of the effluvia from putrid substances) received into the blood, has a power of corrupting the whole mass. Its resolution and sometimes even its smell in the advanced state of a malignant fever, the offensiveness of the sweats and other excretions, the livid spots, blotches, and mortifications incident to this distemper, are proofs of what is here advanced.” Black 8 recalled that “in the seventeenth and eighteenth centuries, intelligent observers of contagious diseases, after much study of the subject, came to the conclusion they were caused and propagated by a process identical with or similar to fermentation and decomposition.” Of course not all early scientists agreed with the miasma theory; for example, Bell9 rejected the concept of a miasma. Schroeder (8, Page 28) tested the concept that air filtered “with cotton batting” would “catch any solid particles in the shape of spores or germs.” Thus, he “conclusively disproved the existence of gaseous ferments claimed by chemists, by admitting air filtered through cotton batting to sterilized fluids without causing fermentation.” The miasma theory existed long before the filth theory, and the latter may be considered as a modification of the former. Without knowing the exact causes of diseases, people adopted the filth theory and considered everything dirty to be lethal. Since then, of course, the success of the germ theory of disease has become well-known. One may also appreciate the contributions of the miasma theory of disease to the development of the germ theory. Based on the miasma theory, bacteriologists knew where to find the causative pathogens of specific diseases (eg, sick patients or dead bodies). The well-known successes of the miasma and filth theories of disease likely led to broad efforts to improve sanitation and hygiene. By the early 20th century, Chapin10 recognized that “until very recently it was thought that the air was the chief vehicle of infection. This was but natural. No one could see infection and what was more natural than to think it gaseous like the invisible air.” Equipped with knowledge about targeted pathogens, “we are no longer in terror of some all-pervading epidemic influence from which there is no escape. We do not worry about the ‘fall fever’ which came regularly and mysteriously, for we now know just how typhoid fever is spread and how it can be avoided…Science allays fear by substituting light for darkness.” We can certainly imagine the terror and fear that a “fall fever” would have caused at that time. From the viewpoint of health, I have personally divided history in a simplistic manner. In the 18th and 19th centuries, urbanization in Europe and subsequently in the United States led to the general filth theory (association) of diseases. Since the 1870s and mostly in the 20th century, the discoveries by Pasteur and Koch of specific microbes responsible for particular infectious diseases led to the germ theory (cause) of disease, which eventually led engineers and physicians to work separately and to achieve wonderful progress. I prefer to describe the filth or miasma theory as the general environment theory, or the assumption that all filth can spread disease and thus all filthy places and objects (eg, air, water, food, soil, clothing, dwellings, streets, and cities) must be cleaned. To some degree, one may also argue that the general environment theory is more holistic than the germ theory of the 19th century. Although recent knowledge has demonstrated the inaccuracy of the filth theory, it provides a foundation upon which humans can implement measures of hygiene at all levels and scales (ie, individual and community, buildings and cities). The filth theory led to hygiene improvement efforts on all fronts in Europe and America and to a significant reduction in disease through various efforts, including those made by Pettenkofer. Locher summarized that, “the measures Pettenkofer recommended to combat the epidemic not only drastically reduced the risk of cholera outbreaks, but also contributed to a substantial reduction of the morbidity rate for typhoid fever”.1 Reports of many of these early works are now readily accessible online. For example, my search of Google Books and archive.org for books and articles published before 1900 with titles containing the keyword “ventilation” or “foul air” produced a long list of relevant texts. Some of these books were written by physicians with different levels of sophistication. Notably, few textbooks on building ventilation have been written by physicians since 1900. The field of building ventilation has become an engineering specialty. In fact, building ventilation design has become so specialized that it is practiced by a special group of engineers, including mechanical engineers in the Americas, building services engineers in the UK and Hong Kong, China, and HVAC engineers in mainland China. It is important to recognize that the broad view of the environment in the 18th and 19th centuries along with new discoveries in chemistry and microbiology and the development of associated research tools led to the study of many aspects of the environment, including ventilation. Pettenkofer's discovery of carbon dioxide as an indicator of indoor ventilation is a good example.2 Scientific communities often divide the world into pieces, aiming to understand one piece at a time (ie, the basic reductionism approach). Such analyses of one pathogen, one chemical, one component, or one aspect have enabled indoor air science efforts to focus on one attribute and thus pinpoint exact mechanisms and specific intervention methods. Other scientists may choose a different approach and study several or all aspects of an issue concomitantly, rather than a single aspect in a piecemeal manner. This latter approach may describe the attitude of Pettenkofer, who seemed to have preferred what is currently called a holistic approach. Pettenkofer believed that clean drinking water, pure air, good food, and a “good dwelling” were necessary for a “healthy, comfortable life.”1 According to Fang and Casadevall, “reductionism may prevent scientists from recognizing important relationships between components or organisms in their natural settings”.11 According to traditional Chinese wisdom, this concept is referred to as “treating the head when the head aches, and treating the foot when the foot hurts” (in Chinese, 頭痛醫頭、腳痛醫腳). “Holism, on the other hand, is inherently more challenging due to the complexity of living organisms in their environment”.11 Fang and Casadevall11 also cited Richard Dawkins, who said that “reductionism is one of those things, like sin, that is only mentioned by people who are against it.” As demonstrated here, reductionism and holism coexist in the history of the indoor air sciences. Indoor air is an environmental system, and studies of this system must consider many aspects, including physical, chemical, biological, psychological, behavioral, social, and architectural. Indoor air also interacts with the human body, thereby influencing human wellbeing. Effective studies in the indoor air sciences require both reductionism and holism. Currently, we are facing the challenges of the 21st century, and both holistic and reductionist approaches toward diseases and health, and specifically for the indoor air environment and health, are needed more than ever. There is an apparent need for multidisciplinary and interdisciplinary research in the field, consistent with the background against which the Indoor Air journal was first established. A combined consideration of holism and reductionism can be powerful and synergistic. I recently read a paper by Wildner and Hofman,13 who further explained the dramatic germ swallowing event by Pettenkofer. Below, I have reproduced some interesting excerpts from that paper: This story led me to imagine the germ swallowing event as a nonverbal “debate” about the holistic and reductionist approaches. Although this may be an overstatement, it appears that Pettenkofer indeed preferred “broader epidemiologic considerations” and refused to accept “Robert Koch's exclusive focus on bacteriology.” I consider this to be a major difference between the two theories, or at least between the approaches and philosophies underlying the theories. As we revisit the history of indoor air science while standing on the shoulders of giants in the field, we will hopefully be able to see further, wider and deeper into the roles of indoor air environment for human health. Indoor air sciences require both breadth and depth. That we collectively incorporate both holistic and reductionist perspectives is consistent with the wisdom of the founders of the Indoor Air journal in its multidisciplinary and scientific nature. None.
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