William F. Wells

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William Firth Wells (c. 1886 - 9 September 1963) was an American scientist and sanitary engineer. In his early career, he pioneered techniques for the aquaculture of oysters and clams. He is best known for his work on airborne infections. Wells identified that tuberculosis could be transmitted through air via the nuclei of evaporated respiratory droplets, and developed the Wells curve to describe what happens to respiratory droplets after they have been expelled into the air.

Contents

Biography

Wells was born c. 1886 in Boston, with a sister and two brothers. [1] Wells served in the military during World War I. [2] He married Mildred Weeks, a physician, [3] and had a son. [2]

Wells was chairman of the American Public Health Association's subcommittee on bacteriologic procedures in air analysis, and chairman of the American Society for Heating and Ventilation Engineers' subcommittee on air sanitation. In 1950, the American Public Health Association honored his 40 years of service. [1]

In 1954, Wells' career moved to Baltimore, Maryland, where he was a research associate at Johns Hopkins University, conducted research at the Veterans Administration Hospital, and consulted on respiratory disease for the Veterans Administration. [1] He and his family lived in a remote part of eastern Maryland. One of his colleagues, Richard L. Riley, described him as "an eccentric genius." [2]

In the late 1950s, Wells collapsed, paralyzed from the waist down. After his initial hospitalization, he was transferred to the VA Hospital in Baltimore where he was overseeing a long-term tuberculosis study. He experienced periods of psychosis but continued to advise on research when lucid. [2] He died on September 9, 1963, at the age of 76. [1]

Research

Aquaculture of oysters and clams

Between 1920 and 1926, Wells pioneered aquaculture techniques to culture bivalves. Wells was experimenting with the recently-invented De Laval milk clarifier, and discovered microscopic oyster larvae in the denser portion of clarified seawater. [4] One previous experimenter, William Keith Brooks, had developed a way to harvest oyster gametes, but the resulting oyster larvae starved to death before they grew large enough to be filtered out of the water. [5] Because they were so small, any attempt to change the water (thus providing new food) would remove the larvae too. [6] Wells's innovation was to use the clarifier to concentrate the larvae. He used Brooks' method to acquire gametes, and grew them to adulthood in clarified seawater. By adding fresh seawater each day, and then using the clarifier to concentrate the larvae, Wells was able to resupply their food without losing them. [4]

With this technique, Wells was the first to successfully cultivate Mercenaria mercenaria clams in captivity. Wells also cultivated the oyster Crassostrea virginica , the mussel Mytilus edulis , the clams Mya arenaria and Spisula solidissima , and the scallop Argopecten irradians . [4]

Other work on oysters included oyster purification with chlorination. [1]

Airborne disease transmission

The Wells curve demonstrates that size determines whether respiratory droplets fall to the ground or rapidly dry out and remain airborne after being exhaled. The Wells falling and evaporation curve of droplets (The Wells Curve).png
The Wells curve demonstrates that size determines whether respiratory droplets fall to the ground or rapidly dry out and remain airborne after being exhaled.

Beginning in the 1930s, Wells' research examined respiratory disease transmission. German bacteriologist Carl Flügge in 1899 was the first to show that microorganisms in droplets expelled from the respiratory tract are a means of disease transmission. The term Flügge droplet was sometimes used for particles that are large enough to not completely dry out. [7] Flügge's concept of droplets as primary source and vector for respiratory transmission of diseases prevailed into the 1930s until Wells differentiated between large and small droplets. [8] [9] Wells' major contribution was to show that the nuclei of evaporated droplets can remain in the air for long enough for others to breathe them in and become infected. [10] He and his wife developed the Wells curve, which describes how the size of respiratory droplets influences their fate and thus their ability to transmit disease. [3] [11] With Richard L. Riley, he also developed the Wells-Riley equation "to express the mass balance of transmission factors under steady state conditions." [12]

In 1935, Wells demonstrated that ultraviolet germicidal irradiation (UVGI), which had been used to kill microorganisms on surfaces and in liquids, could also be used to kill airborne infectious organisms. This experiment proved that he had been correct that droplet nuclei could be infectious, and also suggested a route for prevention. In 1935, Wells helped develop UVGI barriers for the Infants' and Children's Hospital in Boston, using cubicle-like rooms subjected to high-intensity UV light to reduce cross-contamination. From 1937 to 1941, Wells implemented a long-term study using upper-room UVGI, that is, UVGI which only sterilized the area above people's heads, allowing the room to be occupied at the time but relying on vertical ventilation to ensure the occupants breathe sterilized air. This study installed upper-room UVGI in suburban Philadelphia schools to prevent the spread of measles. [10]

Wells first proposed the idea of airborne droplet nucleus transmission of tuberculosis in the 1930s. He demonstrated that rabbits could be infected with bovine TB through droplets. [2] In 1954, Wells began a long-term experiment to demonstrate that tuberculosis could be transmitted through air. At the VA Hospital in Baltimore, collaborating with Riley, John Barnwell, and Cretyl C. Mills, he built a chamber for 150 guinea pigs to be exposed to air from infectious patients in a nearby TB ward. After two years, they found that an average of three guinea pigs a month were indeed infected. Although this was exactly the rate Wells had predicted, skeptics complained that other methods of transmission (such as the animals' food and water) had not been conclusively ruled out. A second long-term study was begun, this time with a second chamber for an additional 150 guinea pigs, whose air was sterilized with UVGI. The animals in the second room did not become ill, proving that the only transmission vector in the first room was the air from the tuberculosis ward. The study was completed in 1961, and published in 1962, though Wells did not see the final paper. [2]

Wells' 1955 book Air Contagion and Air Hygiene has been described as the authoritative book on the subject and a "landmark monograph on air hygiene." [10] It drew on 23 years of research. [1]

Posthumous relevance to COVID-19 pandemic

A major area of scientific inquiry during the COVID-19 pandemic was the disease's method of transmission, and especially the distinction between "droplet" transmission or "airborne" transmission, since different public health measures would be required depending on the transmission vector. Wells' work on droplet size and the airborne transmission of tuberculosis has been cited as important and influential research to support the identification of COVID-19 as airborne, even when particles exceeded 5 microns in size. [3] [13]

Major works

Related Research Articles

In medicine, public health, and biology, transmission is the passing of a pathogen causing communicable disease from an infected host individual or group to a particular individual or group, regardless of whether the other individual was previously infected. The term strictly refers to the transmission of microorganisms directly from one individual to another by one or more of the following means:

<span class="mw-page-title-main">Surgical mask</span> Mouth and nose cover against bacterial aerosols

A surgical mask, also known by other names such as a medical face mask or procedure mask, is a personal protective equipment used by healthcare professionals that serves as a mechanical barrier that interferes with direct airflow in and out of respiratory orifices. This helps reduce airborne transmission of pathogens and other aerosolized contaminants between the wearer and nearby people via respiratory droplets ejected when sneezing, coughing, forceful expiration or unintentionally spitting when talking, etc. Surgical masks may be labeled as surgical, isolation, dental or medical procedure masks.

<span class="mw-page-title-main">Natural reservoir</span> Type of population in infectious disease ecology

In infectious disease ecology and epidemiology, a natural reservoir, also known as a disease reservoir or a reservoir of infection, is the population of organisms or the specific environment in which an infectious pathogen naturally lives and reproduces, or upon which the pathogen primarily depends for its survival. A reservoir is usually a living host of a certain species, such as an animal or a plant, inside of which a pathogen survives, often without causing disease for the reservoir itself. By some definitions a reservoir may also be an environment external to an organism, such as a volume of contaminated air or water.

<span class="mw-page-title-main">Hard clam</span> Species of bivalve mollusc native to the east coast of North and Central America

The hard clam, also known as the round clam, hard-shellclam, or the quahog, is an edible marine bivalve mollusk that is native to the eastern shores of North America and Central America from Prince Edward Island to the Yucatán Peninsula. It is one of many unrelated edible bivalves that in the United States are frequently referred to simply as clams. Older literature sources may use the systematic name Venus mercenaria; this species is in the family Veneridae, the venus clams.

Infection prevention and control is the discipline concerned with preventing healthcare-associated infections; a practical rather than academic sub-discipline of epidemiology. In Northern Europe, infection prevention and control is expanded from healthcare into a component in public health, known as "infection protection". It is an essential part of the infrastructure of health care. Infection control and hospital epidemiology are akin to public health practice, practiced within the confines of a particular health-care delivery system rather than directed at society as a whole.

<span class="mw-page-title-main">Carl Flügge</span> German bacteriologist and hygienist

Carl Georg Friedrich Wilhelm Flügge was a German bacteriologist and hygienist. His finding that pathogens were present in expiratory droplets, the eponymous Flügge droplets, laid ground for the concept of droplet transmission as a route for the spread of respiratory infectious diseases.

Aerobiological engineering is the science of designing buildings and systems to control airborne pathogens and allergens in indoor environments. The most-common environments include commercial buildings, residences and hospitals. This field of study is important because controlled indoor climates generally tend to favor the survival and transmission of contagious human pathogens as well as certain kinds of fungi and bacteria.

<span class="mw-page-title-main">Isolation (health care)</span> Measure taken to prevent contagious diseases from being spread

In health care facilities, isolation represents one of several measures that can be taken to implement in infection control: the prevention of communicable diseases from being transmitted from a patient to other patients, health care workers, and visitors, or from outsiders to a particular patient. Various forms of isolation exist, in some of which contact procedures are modified, and others in which the patient is kept away from all other people. In a system devised, and periodically revised, by the U.S. Centers for Disease Control and Prevention (CDC), various levels of patient isolation comprise application of one or more formally described "precaution".

<span class="mw-page-title-main">Airborne transmission</span> Disease transmission by airborne particles

Airborne transmission or aerosol transmission is transmission of an infectious disease through small particles suspended in the air. Infectious diseases capable of airborne transmission include many of considerable importance both in human and veterinary medicine. The relevant infectious agent may be viruses, bacteria, or fungi, and they may be spread through breathing, talking, coughing, sneezing, raising of dust, spraying of liquids, flushing toilets, or any activities which generate aerosol particles or droplets. This is the transmission of diseases via transmission of an infectious agent, and does not include diseases caused by air pollution.

Influenza prevention involves taking steps that one can use to decrease their chances of contracting flu viruses, such as the Pandemic H1N1/09 virus, responsible for the 2009 flu pandemic.

Transmission-based precautions are infection-control precautions in health care, in addition to the so-called "standard precautions". They are the latest routine infection prevention and control practices applied for patients who are known or suspected to be infected or colonized with infectious agents, including certain epidemiologically important pathogens, which require additional control measures to effectively prevent transmission. Universal precautions are also important to address as far as transmission-based precautions. Universal precautions is the practice of treating all bodily fluids as if it is infected with HIV, HBV, or other blood borne pathogens.

A number of possible health hazards of air travel have been investigated.

<span class="mw-page-title-main">Wells curve</span> Science of medicine

The Wells curve is a diagram, developed by W. F. Wells in 1934, which describes what is expected to happen to small droplets once they have been exhaled into air. Coughing, sneezing, and other violent exhalations produce high numbers of respiratory droplets derived from saliva and/or respiratory mucus, with sizes ranging from about 1 µm to 2 mm. Wells' insight was that such droplets would have two distinct fates, depending on their sizes. The interplay of gravity and evaporation means that droplets larger than a humidity-determined threshold size would fall to the ground due to gravity, while droplets smaller than this size would quickly evaporate, leaving a dry residue that drifts in the air. Since droplets from an infected person may contain infectious bacteria or viruses, these processes influence transmission of respiratory diseases.

<span class="mw-page-title-main">Respiratory droplet</span> Type of particle formed by breathing

A respiratory droplet is a small aqueous droplet produced by exhalation, consisting of saliva or mucus and other matter derived from respiratory tract surfaces. Respiratory droplets are produced naturally as a result of breathing, speaking, sneezing, coughing, or vomiting, so they are always present in our breath, but speaking and coughing increase their number.

A toilet plume is the dispersal of microscopic particles as a result of flushing a toilet. Normal use of a toilet by healthy individuals is considered unlikely to be a major health risk. However this dynamic changes if an individual is fighting an illness and currently shedding out a virulent pathogen in their urine, feces or vomitus. There is indirect evidence that specific pathogens such as norovirus or SARS coronavirus could potentially be spread by toilet aerosols, but as of 2015, no direct experimental studies had clearly demonstrated or refuted actual disease transmission from toilet aerosols. It has been hypothesized that dispersal of pathogens may be reduced by closing the toilet lid before flushing, and by using toilets with lower flush energy.

Lydia Bourouiba is an Esther and Harold E. Edgerton Professor, an Associate Professor in the Civil and Environmental Engineering and Mechanical Engineering departments, and in the Institute for Medical Engineering and Science at the Massachusetts Institute of Technology. She is also a Harvard-MIT Health Sciences and Technology Faculty, and Affiliate Faculty of Harvard Medical School. She directs the Fluid Dynamics of Disease Transmission Laboratory at MIT.

<span class="mw-page-title-main">Source control (respiratory disease)</span> Strategy for reducing disease transmission

Source control is a strategy for reducing disease transmission by blocking respiratory secretions produced through speaking, coughing, sneezing or singing. Surgical masks are commonly used for this purpose, with cloth face masks recommended for use by the public only in epidemic situations when there are shortages of surgical masks. In addition, respiratory etiquette such as covering the mouth and nose with a tissue when coughing can be considered source control. In diseases transmitted by droplets or aerosols, understanding air flow, particle and aerosol transport may lead to rational infrastructural source control measures that minimize exposure of susceptible persons.

<span class="mw-page-title-main">Transmission of COVID-19</span> Mechanisms that spread coronavirus disease 2019

The transmission of COVID-19 is the passing of coronavirus disease 2019 from person to person. COVID-19 is mainly transmitted when people breathe in air contaminated by droplets/aerosols and small airborne particles containing the virus. Infected people exhale those particles as they breathe, talk, cough, sneeze, or sing. Transmission is more likely the closer people are. However, infection can occur over longer distances, particularly indoors.

Droplet nuclei are aerosols formed from the evaporation of respiratory droplets. They are generally smaller than 5 μm in diameter. Droplet nuclei are formed by the "dried residua of larger respiratory droplets". These particles are "the vehicle for airborne respiratory disease transmission, which are the dried-out residual of droplets possibly containing infectious pathogens". Diseases such as tuberculous and COVID-19 can be transmitted via droplet nuclei.

The Wells-Riley model is a simple model of the airborne transmission of infectious diseases, developed by William F. Wells and Richard L. Riley for tuberculosis and measles.

References

  1. 1 2 3 4 5 6 "William Firth Wells". The Evening Sun. 1963-10-10. Retrieved 2021-03-24.
  2. 1 2 3 4 5 6 Riley, Richard L. (2001-01-01). "What Nobody Needs to Know About Airborne Infection". American Journal of Respiratory and Critical Care Medicine. 163 (1): 7–8. doi:10.1164/ajrccm.163.1.hh11-00. ISSN   1073-449X. PMID   11208616.
  3. 1 2 3 "The 60-Year-Old Scientific Screwup That Helped Covid Kill". Wired. ISSN   1059-1028 . Retrieved 2021-05-15.
  4. 1 2 3 Kraeuter, J.N.; Castagna, M., eds. (2001). Biology of the hard clam. Elsevier. p. 675. ISBN   978-0-444-81908-6. OCLC   162130961.
  5. ↑ Steele, Ralph Emory (5 June 1927). "Sets Up an Oyster Aristocracy". The Brooklyn Daily Eagle.
  6. ↑ "The Popular science monthly. v.098 yr.1921 mo.JAN-JUN". HathiTrust. Retrieved 2021-03-24.
  7. ↑ Hare, R. (1964-03-01). "The transmission of respiratory infections". Proceedings of the Royal Society of Medicine. 57 (3): 221–230. doi:10.1177/003591576405700329. ISSN   0035-9157. PMC   1897886 . PMID   14130877.
  8. ↑ Wells, W. F. (1934). "On air-borne infection: study II. Droplets and droplet nuclei". American Journal of Epidemiology. 20 (3): 611–618. doi:10.1093/oxfordjournals.aje.a118097.
  9. ↑ Bourouiba, Lydia (2020-03-26). "Turbulent Gas Clouds and Respiratory Pathogen Emissions: Potential Implications for Reducing Transmission of COVID-19". JAMA. 323 (18): 1837–1838. doi: 10.1001/jama.2020.4756 . ISSN   0098-7484. PMID   32215590.
  10. 1 2 3 Reed, Nicholas G. (2010). "The History of Ultraviolet Germicidal Irradiation for Air Disinfection". Public Health Reports. 125 (1): 15–27. doi:10.1177/003335491012500105. ISSN   0033-3549. PMC   2789813 . PMID   20402193.
  11. ↑ World Health Organization; Y. Chartier; C. L Pessoa-Silva (2009). Natural Ventilation for Infection Control in Health-care Settings. World Health Organization. p. 79. ISBN   978-92-4-154785-7.
  12. ↑ Donald, P. R.; Diacon, A. H.; Lange, C.; Demers, A.-M.; von Groote-Biddlingmeier, F.; Nardell, E. (2018-09-01). "Droplets, dust and guinea pigs: an historical review of tuberculosis transmission research, 1878–1940". The International Journal of Tuberculosis and Lung Disease. 22 (9): 972–982. doi:10.5588/ijtld.18.0173. PMID   30092861. S2CID   51952262.
  13. ↑ Randall, Katherine; Ewing, E. Thomas; Marr, Linsey; Jimenez, Jose; Bourouiba, L. (2021-04-15). "How Did We Get Here: What Are Droplets and Aerosols and How Far Do They Go? A Historical Perspective on the Transmission of Respiratory Infectious Diseases". Rochester, NY. SSRN   3829873.{{cite journal}}: Cite journal requires |journal= (help)
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