Selected patients may require specific precautions to limit transmission of potential infecting organisms to other patients. Recommended isolation precautions depend on the route of transmission (1). The main routes are:
Airborne transmission occurs when infectious agents are carried by dust suspended in the air. With airborne transmission, direct contact is not needed to spread disease (as compared with respiratory droplet transmission). Infection may be transmitted over short distances by large droplets, and at longer distances by droplet nuclei generated by coughing and sneezing. Airborne transmission is totally different from respiratory (droplet) transmission. With respiratory disease, the disease-causing bacteria and viruses are carried in the mouth, nose, throat and respiratory tree. They can spread by coming into direct contact with droplets when an infected person coughs or sneezes, or through saliva or mucus on unwashed hands. With airborne transmission, droplet nuclei remain airborne for long periods, may disseminate widely in an environment such as a hospital ward or an operating room, and can be acquired by (and infect) patients directly, or indirectly through contaminated medical devices. Housekeeping activity such as sweeping, using dry dust mops or cloths, or shaking out linen, can aerosolize particles that may contain microorganisms. Similarly, Legionella pneumophila, the organism responsible for legionellosis (Legionnaires’ disease; Pontiac fever), can become airborne during the evaporation of water droplets from air conditioning cooling towers or with aerosolization in patient showers, and subsequently may be inhaled by patients at risk of infection. The number of organisms present in room air will depend on the number of people occupying the room, the amount of activity, and the rate of air exchange. Bacteria recovered from air samples usually consist of Gram-positive cocci originating from the skin. They can reach large numbers if dispersed from an infected lesion, particularly an infected exfoliative skin lesion. However, since the contaminated skin scales are relatively heavy, they do not remain suspended in the air for long. Gram-negative bacteria are usually found in the air only when associated with aerosols from contaminated fluids, and tend to die on drying. Droplets projected from the infected upper respiratory tract may contain a wide variety of microrganisms, including viruses, and many infections can be spread by this route (i.e. respiratory viruses, influenza, measles, chickenpox, tuberculosis). In most cases, these are spread by large droplets, and an infective dose will rarely move more than a few feet from the source patient. Varicella-zoster (chickenpox), tuberculosis, and a few other agents, however, may be transmitted over large distances in droplet nuclei. Fresh filtered air, appropriately circulated, will dilute and remove airborne bacterial contamination. It also eliminates smells. Desirable ventilation rates, expressed in air changes per hour, vary with the purpose of a particular area. High-risk hospital areas (operating rooms, nurseries, intensive care units, oncology, and burn units) should have air with minimal bacterial contamination. Modern operating rooms which meet current air standards are virtually free of particles larger than 0.5 μm (including bacteria) when no people are in the room. For more information, consult our last article regarding the hygienic air treatment, and do not hesitate to contact us through our contact form. * This article comes from the WHO » Prevention of hospital-acquired infections » practical guide. Airborne or aerosol transmission is transmission of an infectious disease through small particles suspended in the air.[2] 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.
Video explainer on reducing airborne pathogen transmission indoors This is the transmission of diseases via transmission of an infectious agent, and does not include diseases caused by air pollution. Aerosol transmission has traditionally has been considered distinct from transmission by droplets, but this distinction is no longer used.[3][4] Respiratory droplets were thought to rapidly fall to the ground after emission:[5] but smaller droplets and aerosols also contain live infectious agents, and can remain in the air longer and travel farther.[4] Individuals generate aerosols and droplets across a wide range of sizes and concentrations, and the amount produced varies widely by person and activity.[6] Larger droplets greater than 100 μm usually settle within 2 m.[6][5] Smaller particles can carry airborne pathogens for extended periods of time. While the concentration of airborne pathogens is greater within 2m, they can travel farther and concentrate in a room.[4] The traditional size cutoff of 5 μm between airborne and respiratory droplets has been discarded, as exhaled particles form a continuum of sizes whose fates depend on environmental conditions in addition to their initial sizes. This error has informed hospital based transmission based precautions for decades.[6] Indoor respiratory secretion transfer data suggest that droplets/aerosols in the 20 μm size range initially travel with the air flow from cough jets and air conditioning like aerosols,[7] but fall out gravitationally at a greater distance as "jet riders".[8] As this size range is most efficiently filtered out in the nasal mucosa,[9] the primordial infection site in COVID-19, aerosols/droplets[10] in this size range may contribute to driving the COVID-19 pandemic. Airborne diseases can be transmitted from one individual to another through the air. The pathogens transmitted may be any kind of microbe, and they may be spread in aerosols, dust or droplets. The aerosols might be generated from sources of infection such as the bodily secretions of an infected individual, or biological wastes. Infectious aerosols may stay suspended in air currents long enough to travel for considerable distances; sneezes, for example, can easily project infectious droplets for dozens of feet (ten or more meters).[11] Airborne pathogens or allergens typically enter the body via the nose, throat, sinuses and lungs. Inhalation of these pathogens affects the respiratory system and can then spread to the rest of the body. Sinus congestion, coughing and sore throats are examples of inflammation of the upper respiratory airway. Air pollution plays a significant role in airborne diseases. Pollutants can influence lung function by increasing air way inflammation.[12] Common infections that spread by airborne transmission include COVID-19;[13] measles morbillivirus,[14] chickenpox virus;[15] Mycobacterium tuberculosis, influenza virus, enterovirus, norovirus and less commonly coronavirus, adenovirus, and possibly respiratory syncytial virus.[16] Poor ventilation enhances transmission by allowing aerosols to spread undisturbed in an indoor space.[17] Crowded rooms are more likely to contain an infected person. The longer a susceptible person stays in such a space, the greater chance of transmission. Airborne transmission is complex, and hard to demonstrate unequivocally[18] but the Wells-Riley model can be used to make simple estimates of infection probability.[19] Some airborne diseases can affect non-humans. For example, Newcastle disease is an avian disease that affects many types of domestic poultry worldwide that is airborne.[20] Airborne transmission can be classified as obligate, preferential, or opportunistic. Obligate airborne infections spread only through aerosols; the most common example of this category is tuberculosis. Preferential airborne infections, such as chicken pox, can be obtained through different routes, but mainly by aerosols. Opportunistic airborne infections such as influenza typically transmit through other routes; however, under favourable conditions, aerosol transmission can occur.[21] Because the drying process can damage the pathogens, the number of airborne diseases is limited.[15] Environmental factors influence the efficacy of airborne disease transmission; the most evident environmental conditions are temperature and relative humidity.[22][23] The transmission of airborne diseases is affected by all the factors that influence temperature and humidity, in both meteorological (outdoor) and human (indoor) environments. Circumstances influencing the spread of droplets containing infectious particles can include pH, salinity, wind, air pollution, and solar radiation as well as human behavior.[24] Airborne infections usually land in the respiratory system, with the agent present in aerosols (infectious particles < 5 µm in diameter).[25] This includes dry particles, often the remnant of an evaporated wet particle called nuclei, and wet particles.
A layered risk-management approach to slowing the spread of a transmissible disease attempts to minimize risk through multiple layers of interventions. Each intervention has the potential to reduce risk. A layered approach can include interventions by individuals (e.g. mask wearing, hand hygiene), institutions (e.g. surface disinfection, ventilation, and air filtration measures to control the indoor environment), the medical system (e.g. vaccination) and public health at the population level (e.g. testing, quarantine, and contact tracing).[4] Preventive techniques can include disease-specific immunization as well as nonpharmaceutical interventions such as wearing a respirator and limiting time spent in the presence of infected individuals.[37] Wearing a face mask can lower the risk of airborne transmission to the extent that it limits the transfer of airborne particles between individuals.[38] The type of mask that is effective against airborne transmission is dependent on the size of the particles. While fluid-resistant surgical masks prevent large droplet inhalation, smaller particles which form aerosols require a higher level of protection with filtration masks rated at N95 (US) or FFP3 (EU) required.[39] Use of FFP3 masks by staff managing patients with COVID-19 reduced acquisition of COVID-19 by staff members.[40] Engineering solutions which aim to control or eliminate exposure to a hazard are higher on the hierarchy of control than personal protective equipment (PPE). At the level of physically based engineering interventions, effective ventilation and high frequency air changes, or air filtration through high efficiency particulate filters, reduce detectable levels of virus and other bioaerosols, improving conditions for everyone in an area.[4][41] Portable air filters, such as those tested in Conway Morris A et al. present a readily deployable solution when existing ventilation is inadequate, for instance in repurposed COVID-19 hospital facilities.[41] The United States Centers for Disease Control and Prevention (CDC) advises the public about vaccination and following careful hygiene and sanitation protocols for airborne disease prevention.[42] Many public health specialists recommend physical distancing (also known as social distancing) to reduce transmission.[43] A 2011 study concluded that vuvuzelas (a type of air horn popular e.g. with fans at football games) presented a particularly high risk of airborne transmission, as they were spreading a much higher number of aerosol particles than e.g., the act of shouting.[44] Exposure does not guarantee infection, as infection is dependent on host immune system competency plus the quantity of infectious particles ingested.[37]Antibiotics may be used in dealing with airborne bacterial primary infections, such as pneumonic plague.[45]
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