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The Social Construction of Airborne Infections
Published in AnnaMarie Bliss, Dak Kopec, Architectural Factors for Infection and Disease Control, 2023
Pathogens capable of airborne transmission are those that travel within aerosolized particles small enough to linger in the air for extended periods. This mode is considered indirect person-to-person transmission. While many pathogens can travel through the air, true airborne transmission is delineated by particle size, which is dependent on several factors: the size of the pathogen, the material that carries the pathogen, and the pressure when projected into the air. Particle size is also determined by environmental factors including humidity, temperature, sunshine, and airflow. Larger droplets remain in the air for minutes at most before being overcome by the force of gravity and falling onto surfaces or onto the ground. Droplets tend to transmit in a spray, which is why this mode of transmission is sometimes referred to as spray-borne or droplet-spray. Droplets can infect people in close proximity through deposition on mucous membranes like the nostrils, lips, or eyes. By contrast, finer droplets dry quickly, forming into what is known as droplet nuclei. By virtue of a smaller size, droplet nuclei can stay suspended in the air for hours, travel farther distances, and cause infection through inhalation. Traditionally, the latter phenomenon is considered airborne transmission. As is true for TB, pathogens that are considered airborne spread through the coughing, sneezing, speaking, singing, or laughing of a person with an active infection. Airborne particles, like smoke, float in the air and are transmitted into the lungs of those with whom they share close, poorly ventilated quarters.
Impact of Indoor Air Pathogens on Human Health
Published in Richard B. Gammage, Stephen V. Kaye, Vivian A. Jacobs, Indoor Air and Human Health, 2018
Although most of these infections are of viral etiology, bacterial diseases such as tuberculosis, streptococcal pneumonia, and meningococcal meningitis do occur and have caused substantial problems in hospitals, hotels, day care centers, nursing homes, mental institutions, and schools. Most of these diseases are spread via person-to-person. This is by either close contact such as kissing, hugging, and touching or by “droplets” or “droplet nuclei” present in the air. Droplets emanate from the mouth or the nose during talking, singing, coughing, or sneezing. Those of large size usually drop to the floor within 1 meter. Smaller “droplets” can dry and form “droplet nuclei” which can remain suspended in the air for long periods of time. They are the only ones that should be considered truly airborne [1], Particles less than 5 microns in size can easily penetrate to the alveoli of the human lung [2]. If they are viable, virulent, and in sufficient number, infection can result. Since these particles can be circulated by air-handling systems, they should be the concern of all who are interested in air quality and its effect on human health.
Introduction to Coronaviruses and COVID-19
Published in Joystu Dutta, Srijan Goswami, Abhijit Mitra, COVID-19 and Emerging Environmental Trends, 2020
Joystu Dutta, Srijan Goswami, Abhijit Mitra
There are two basic ways by which an individual can get infected by SARS-CoV-2: one is through the “respiratory droplets,” and the other is through “droplet nuclei” (WHO, 2020a). Respiratory droplets are droplet particles that are >5–10 μm in diameter, whereas droplet particles of size <5μm in diameter are called droplet nuclei (WHO, 2014). Several researchers have reported that respiratory droplets and contact routes are the primary modes of transmission between individuals (Liu et al., 2020; Chan et al., 2020; Li et al., 2020; Burke et al., 2020; WHO, 2020a). Transmission through droplets is possible when an individual is in close contact (generally within 1 m) with the infected person (See Figure 1.6). The infected person may transmit the virus through a cough or sneeze or sometimes just by talking (without protective masks), and as a result, the mucosa (nose and mouth) and conjunctiva (eyes) of the healthy person may get exposed to potentially infective respiratory droplets (Ong et al., 2020). The virus can also get transmitted through fomites (Ong et al., 2020). Fomites are the objects contaminated with infectious agents (in this case the SARS-CoV-2) and serve in their transmission. Therefore, direct contact with an infected individual and indirect contact with fomites are the major ways by which SARS-CoV-2 can get transmitted (See Figures 1.5 and 1.6). Sometimes, the droplet nuclei (containing the pathogen) remains in the air for a long period of time and gets transmitted to individuals over distances greater than 1 meter. This phenomenon is called airborne transmission. Airborne transmission of COVID-19 is possible under specific circumstances in which aerosol production is facilitated. Endotracheal intubation, noninvasive positive pressure ventilation, and disconnecting a patient from the ventilators are some of the situations (among many) that can lead to airborne transmission (WHO, 2020a). A group of researchers from China reported that COVID-19 may give rise to intestinal symptoms and that the viral particles may be present in the feces of the patient (Zhang et al., 2020). According to WHO, no report of fecal–oral transmission of COVID-19 has been reported until June 30, 2020 (WHO, 2020). Figure 1.5 represents the sequence of transmission of COVID-19.
Effect of air cleaner on reducing concentration of indoor-generated viruses with or without natural ventilation
Published in Aerosol Science and Technology, 2021
Jungsuk Lee, Su-Hoon Park, Gi-Bong Sung, Ik-Hyun An, Kyung-Rae Lee, Sung-Pyo Hong, Se-Jin Yook, Hyun Bon Koo
As coronavirus disease (COVID-19), a novel virus, is known to be highly infectious worldwide, the interest in eliminating the virus and reducing its spread has been increasing. In particular, as the probability of infection increases with the increase in the number of people residing in a closed indoor space, proper ventilation is very important for reducing the spread of the viruses generated indoors. The spread of viruses can be caused by droplet transmission, airborne transmission, or fomite transmission (Wei and Li 2016; Chen et al. 2020). Droplets larger than 5 μm are referred to as respiratory droplets, and the droplet transmission from an infected person to a susceptible person can occur within 1 m distance; while droplets smaller than 5 μm are called droplet nuclei or aerosols, and the airborne transmission, meaning the dissemination of aerosols, can occur over long distance and time (World Health Organization 2020). Many studies have reported that the COVID-19 spreads mainly by droplet transmission. However, saliva droplets that reduced in size after evaporation can remain suspended in the air over an extended period of time (World Health Organization 2014). Therefore, the possibility of airborne infection in a limited space has also been raised (Asadi et al. 2020; Mittal, Ni, and Seo 2020; Morawska and Cao 2020).
Aerosol filtration efficiency of household materials for homemade face masks: Influence of material properties, particle size, particle electrical charge, face velocity, and leaks
Published in Aerosol Science and Technology, 2021
Frank Drewnick, Julia Pikmann, Friederike Fachinger, Lasse Moormann, Fiona Sprang, Stephan Borrmann
The fate and hazardousness of potentially virus-containing droplets after exhalation strongly depends on their size. Small droplets, smaller than several tens of µm, evaporate within seconds (Morawska et al. 2009; Gralton et al. 2011; Parienta et al. 2011; Chaudhuri et al. 2020), leaving droplet nuclei of 30–50% of their initial diameter, depending on the amount of dissolved material. Droplet nuclei with dp < 10 µm can remain airborne over extended periods of time and can be inhaled, with smaller particles reaching deeper regions of the respiratory system (Oberdörster, Oberdörster, and Oberdörster 2005). Very large droplets, dp > 100 µm, sediment quickly and are mostly deposited on a surface before they evaporate (Chaudhuri et al. 2020). The number of virions within a single respiratory particle depends on the virus titer in the source region and increases with the cube of the particle diameter. With SARS-CoV-2 viral loads of 4.6·105 copies per mL of nasopharyngeal sample (Bae et al. 2020), about 20% of exhaled 100 µm diameter droplets would contain a virion; for 10 µm droplets only 2 out of 10,000 particles would contain a virion and for dp = 1 µm droplets this fraction would be another 1000 times smaller.
What aerosol physics tells us about airborne pathogen transmission
Published in Aerosol Science and Technology, 2020
Yannis Drossinos, Nikolaos I. Stilianakis
Contact transmission, be it direct or indirect, occurs via contact with pathogen-laden droplets: transfer of pathogens via physical touch between a susceptible and an infected host (e.g., hand contact) is classified as direct contact transmission, whereas transfer mediated by fomites containing settled droplets is classified as indirect contact transmission. Droplet transmission refers to transmission by large droplets (diameter microns) that are transported by the turbulent air flow generated by a violent expiratory event. They are, subsequently, sprayed and directly deposited upon the conjunctiva or mucus membranes of a susceptible host. Since large droplets gravitationally settle rather quickly, droplet transmission is considered important at close range: in still air, a 50-micron droplet crosses a vertical 1.5 m distance in 20 s (Drossinos and Housiadas 2006). Airborne transmission, also referred to as “aerosol transmission,” refers to pathogen transmission via inhalation of small respiratory droplets (typically smaller than 10 microns: a 10-micron droplet settles gravitationally in still air within approximately 9 min). Being relatively small they may deposit deep into the respiratory tract, including the alveolar region. These droplets, often referred to by the confusing term “droplet nuclei,” are small enough to remain airborne for sufficient time to transmit the pathogen. Hence, airborne transmission does not require direct face-to-face contact.