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:
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.
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.
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.
A sneeze guard, sneezeguard, or cough shield is an acrylic or glass screen designed to protect food or people from the exposure to respiratory droplets, which are dispensed when coughing, sneezing, or speaking. Sneeze guards have been in use in restaurants for decades. With the rise of the COVID-19 pandemic, sneeze guards have been installed in public places like offices, schools and retail stores to reduce the risk of infection through respiratory droplets.
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.
Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is a strain of coronavirus that causes COVID-19, the respiratory illness responsible for the COVID-19 pandemic. The virus previously had the provisional name 2019 novel coronavirus (2019-nCoV), and has also been called human coronavirus 2019. First identified in the city of Wuhan, Hubei, China, the World Health Organization designated the outbreak a public health emergency of international concern from January 30, 2020, to May 5, 2023. SARS‑CoV‑2 is a positive-sense single-stranded RNA virus that is contagious in humans.
A dental aerosol is an aerosol that is produced from dental instrument, dental handpieces, three-way syringes, and other high-speed instruments. These aerosols may remain suspended in the clinical environment. Dental aerosols can pose risks to the clinician, staff, and other patients. The heavier particles contained within the aerosols are likely to remain suspended in the air for relatively short period and settle quickly onto surfaces, however, the lighter particles may remain suspended for longer periods and may travel some distance from the source. These smaller particles are capable of becoming deposited in the lungs when inhaled and provide a route of diseases transmission. Different dental instruments produce varying quantities of aerosol, and therefore are likely to pose differing risks of dispersing microbes from the mouth. Air turbine dental handpieces generally produce more aerosol, with electric micromotor handpieces producing less, although this depends on the configuration of water coolant used by the handpiece.
Coronavirus disease 2019 (COVID-19) is a contagious disease caused by the virus SARS-CoV-2. The first known case was identified in Wuhan, China, in December 2019. The disease quickly spread worldwide, resulting in the COVID-19 pandemic.
An N95 filtering facepiece respirator, commonly abbreviated N95 respirator, is a particulate-filtering facepiece respirator that meets the U.S. National Institute for Occupational Safety and Health (NIOSH) N95 classification of air filtration, meaning that it filters at least 95% of airborne particles that have a mass median aerodynamic diameter of 0.3 micrometers. This standard does not require that the respirator be resistant to oil; another standard, P95, adds that requirement. The N95 type is the most common particulate-filtering facepiece respirator. It is an example of a mechanical filter respirator, which provides protection against particulates but not against gases or vapors. An authentic N95 respirator is marked with the text "NIOSH" or the NIOSH logo, the filter class ("N95"), a "TC" approval number of the form XXX-XXXX, the approval number must be listed on the NIOSH Certified Equipment List (CEL) or the NIOSH Trusted-Source page, and it must have headbands instead of ear loops.
A cloth face mask is a mask made of common textiles, usually cotton, worn over the mouth and nose. When more effective masks are not available, and when physical distancing is impossible, cloth face masks are recommended by public health agencies for disease "source control" in epidemic situations to protect others from virus laden droplets in infected mask wearers' breath, coughs, and sneezes. Because they are less effective than N95 masks, surgical masks, or physical distancing in protecting the wearer against viruses, they are not considered to be personal protective equipment by public health agencies. They are used by the general public in household and community settings as protection against both infectious diseases and particulate air pollution.
Mechanical filters are a class of filter for air-purifying respirators that mechanically stops particulates from reaching the wearer's nose and mouth. They come in multiple physical forms.
During the COVID-19 pandemic, face masks or coverings, including N95, FFP2, surgical, and cloth masks, have been employed as public and personal health control measures against the spread of SARS-CoV-2, the virus that causes COVID-19. With the progress of the pandemic, the public interest in face masks as a means of protection was greatly increased, often even before governments implemented mandatory mask-wearing.
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.
Linsey Chen Marr is an American scientist who is the Charles P. Lunsford Professor of Civil and Environmental Engineering at Virginia Tech. Her research considers the interaction of nanomaterials and viruses with the atmosphere. During the COVID-19 pandemic Marr studied how SARS-CoV-2 and other airborne pathogens could be transported in air. In 2023, she was elected to the National Academy of Engineering and named a MacArthur Fellow.
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.
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.
FFP standards refer to the filtering half mask classification by EN 149, a European standard of testing and marking requirements for filtering half masks. FFP standard masks cover the nose, mouth and chin and may have inhalation and/or exhalation valves.
Part of managing an infectious disease outbreak is trying to delay and decrease the epidemic peak, known as flattening the epidemic curve. This decreases the risk of health services being overwhelmed and provides more time for vaccines and treatments to be developed. Non-pharmaceutical interventions that may manage the outbreak include personal preventive measures such as hand hygiene, wearing face masks, and self-quarantine; community measures aimed at physical distancing such as closing schools and cancelling mass gathering events; community engagement to encourage acceptance and participation in such interventions; as well as environmental measures such surface cleaning. It has also been suggested that improving ventilation and managing exposure duration can reduce transmission.
Nicole M. Bouvier is an American physician who is Professor of Medicine at Icahn School of Medicine at Mount Sinai. Her research considers the environmental and viral factors that impact respiratory transmission of influenza viruses.
