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Welcome to a WiRED Educational Course
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Airborne Diseases
Additional Resources
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WHO: Infection Prevention & Control of Epidemic and Pandemic-prone Acute Respiratory Infections
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CDC: Understand How Infectious Diseases Spread
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CDC: Global WASH Program
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CDC: Improving Child Development
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Guidance for Schools and Districts about Ebola
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Cover Your Cough
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Field Manual: Communicable Disease Control in Emergencies
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WHO: 4 steps for Sound Management of Healthcare Waste in Emergencies
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WHO: Food Safety
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Community Mitigation Strategy
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CDC: Resources for Households
Terms
Acute respiratory diseases (ARDs) are upper or lower respiratory tract illnesses, usually infectious in etiology, which can result in a spectrum of illnesses ranging from asymptomatic or mild infection to severe and fatal disease, depending on the causative pathogen, environmental, and host factors. However, for the purposes of this module, an ARD is defined as an acute respiratory tract illness that is caused by an infectious agent transmitted from person to person. The onset of symptoms is typically rapid, over a period of hours to several days. Symptoms include fever, cough, and often sore throat, coryza, and shortness of breath, wheezing, or difficulty breathing. Examples of pathogens causing ARDs included in these guidelines are rhinovirus, respiratory syncytial virus, parainfluenza virus, severe acute respiratory syndrome-associated coronavirus (SARS-CoV) and influenza virus.
(ARDs of potential concern) Infections in which the pathogens can cause outbreaks on a large scale or with high morbidity and mortality. Examples include SARS-CoV; new influenza virus causing human infection; and novel ARDs that can cause large-scale outbreaks and outbreaks with high morbidity and mortality.
An acute respiratory tract disease that is caused by an infectious agent. Although the spectrum of symptoms of acute respiratory infection (ARI) may vary, the onset of symptoms is typically rapid, ranging from hours to days after infection. Symptoms include fever, cough and, often, sore throat, shortness of breath, wheezing, or difficulty in breathing. The pathogens that cause this disease include influenza virus, parainfluenza virus, rhinovirus, respiratory syncytial virus (RSV) and severe acute respiratory syndrome coronavirus (SARSCoV).
Acute respiratory infections (ARIs) are the leading cause of morbidity and mortality from infectious disease worldwide, particularly affecting the youngest and oldest people in lowand middle-income nations. These infections, typically caused by viruses or mixed viral– bacterial infections, can be contagious and spread rapidly. Although knowledge of transmission modes is ever-evolving, current evidence indicates that the primary mode of transmission of most acute respiratory diseases is through droplets, but transmission through contact (including hand contamination followed by self-inoculation) or infectious respiratory aerosols at short range can also happen for some pathogens in particular circumstances.
A single room, or a side room in the ward, with ≥ 12 air changes per hour (ACH) without controlled direction of air flow. A room or area that has an adequate ventilation rate without controlled direction of airflow. For a naturally ventilated general ward room, adequate ventilation is considered to be 60 litres/second (L/s) per patient. For a mechanically ventilated single room, adequate ventilation is considered to be at least two outdoor air changes (ACH) per hour and at least six total ACH per hour.
The liquid or solid particles that are dispersed in air or another gas, such as dust, particulate air pollutants and smoke.
Procedures that have been reported to be aerosol-generating and associated with a documented increased risk of pathogen transmission. These include intubation and related procedures, cardiopulmonary resuscitation, bronchoscopy, autopsy and surgery where high-speed devices (e.g. saw) are used.
Volume of air moved in one hour. One air change per hour in a room, home, or building means that all the air in that environment will be replaced in one hour.
Air pollution is contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere. Household combustion devices, motor vehicles, industrial facilities and forest fires are common sources of air pollution. Pollutants of major public health concern include particulate matter, carbon monoxide, ozone, nitrogen dioxide and sulfur dioxide. Outdoor and indoor air pollution cause respiratory and other diseases, which can be fatal.
An airborne precaution room is a room with ≥ 12 air changes per hour (ACH) and controlled direction of air flow, and can be used to contain airborne infections and ARDs caused by a novel agent with the potential to have a high public health impact. An airborne precaution room can be naturally or mechanically ventilated. In addition to the requirement of ≥ 12 ACH, in a mechanically ventilated airborne precaution room, negative pressure is created to control the direction of air flow. It is equivalent to the “airborne infection isolation room” described by the United States Centers for Disease Control and Prevention (CDC). In naturally ventilated airborne precaution rooms the air flow should be directed to areas free of transit, or permit the rapid dilution of contaminated air into the surrounding areas and the open air.
Airborne transmission of infectious agents refers to the transmission of disease caused by dissemination of droplet nuclei that remain infectious when suspended in air over long distance and time. Airborne transmission can be further categorized into obligate or preferential airborne transmission.
• Obligate airborne transmission refers to pathogens that are transmitted only by deposition of droplet nuclei under natural conditions (e.g. pulmonary tuberculosis).
• Preferential airborne transmission refers to pathogens that can initiate infection by multiple routes, but are predominantly transmitted by droplet nuclei (e.g. measles, chickenpox).
An alcohol-containing preparation designed for application to the hands for hand antisepsis.
Asthma is a chronic disease characterized by recurrent attacks of breathlessness and wheezing, which vary in severity and frequency from person to person. During an asthma attack, the lining of the bronchial tubes swells, causing the airways to narrow and reducing the flow of air into and out of the lungs. The causes of asthma are not completely understood. However, risk factors for developing asthma include inhaling asthma “triggers”, such as allergens, tobacco smoke and chemical irritants. Asthma cannot be cured, but appropriate management can control the disorder and enable people to enjoy a good quality of life.
A person who provides support and assistance, formal or informal, with various activities to people with disabilities or long-term conditions, or elderly people. This person may provide emotional or financial support, as well as hands-on help with different tasks.
Chronic respiratory diseases (CRDs) are diseases of the airways and other structures of the lung. Some of the most common are chronic obstructive pulmonary disease (COPD), asthma, occupational lung diseases and pulmonary hypertension. In addition to tobacco smoke, other risk factors include air pollution, occupational chemicals and dusts, and frequent lower respiratory infections during childhood. CRDs are not curable, however, various forms of treatment that help dilate major air passages and improve shortness of breath can help control symptoms and increase the quality of life for people with the disease.
Coronaviruses are a large family of viruses that can cause diseases ranging from the common cold to Severe Acute Respiratory Syndrome (SARS). Viruses of this family also cause a number of animal diseases. Novel coronavirus is a particular strain of coronavirus that has not been previously identified in humans. There is very limited information on transmission, severity and clinical impact with only a small number of cases reported thus far.
A process that eliminates all pathogenic microorganisms, with the exception of bacterial spores, from inanimate objects, for the purpose of minimizing risk of infection.
Small particles of pathogen containing respiratory secretions expelled into the air by coughing, which are reduced by evaporation to small, dry particles that can remain airborne for long periods; one possible mechanism for transmission of infection from one individual to another.
Droplets are generated from an infected (source) person primarily during coughing, sneezing, and talking. Transmission occurs when these droplets containing microorganisms are propelled a short distance (usually < 1m) through the air and deposited on the conjunctivae, mouth, nasal, throat or pharynx mucosa of another person. Because droplets do not remain suspended in the air, special air handling and ventilation are not required to prevent droplet transmission.
Use of mechanical fans to introduce and distribute outdoor and/or properly treated recycled air into a building or a room.
Natural ventilation uses natural forces to introduce and distribute outdoor air into a building. These natural forces can be wind pressure or pressure generated by the density difference between indoor and outdoor air.
A general term that applies to hand washing, antiseptic hand washing, antiseptic hand rubbing, or surgical hand antisepsis.
All persons employed or contracted to provide health services.
Any establishment that is engaged in direct patient care on site.
Clinical context where health care is provided (e.g. hospital, outpatient clinic, home).
A variety of professionals (medical practitioners, nurses, physical and occupational therapists, social workers, pharmacists, spiritual counsellors, etc) who are involved in providing coordinated and comprehensive care.
An acute contagious viral infection, commonly occurring in seasonal epidemics (seasonal influenza) or rarely pandemics (pandemic influenza), characterized by inflammation of the respiratory tract, and typically manifested by the sudden onset of fever, chills, muscular pain, severe prostration, sore throat, and cough. Transmission of infection occurs at close range, mainly through droplets and occasionally through contact. To date, there is a lack of evidence to suggest that the infection is airborne-transmitted among humans in health-care settings.
Respiratory aerosols which contain infectious particles. Aerosol size is determined by the force and pressure involved in the generation of the particles. The final size depends on the nature of the fluid containing the organism(s), the force and pressure at emission, the initial size of the aerosol, environmental conditions (e.g. temperature, relative humidity, and air flow), the time spent airborne, and the size of the organism(s) within a droplet. The distance and length of time particles remain suspended in the air is determined by the types of organisms, particle size, settling velocity, relative humidity and air flow.
• Large particles typically remain suspended in the air for limited period of time and settle within 1 m (3 feet) of the source.
• Smaller particles evaporate quickly, and the resulting dried residues settle from the air slowly, and may remain suspended in the air for variable lengths of time.
The definitions and classification of the different types of infectious respiratory aerosols are evolving, and the implications for the infection control measures are not yet clear. However, for the purpose of this document, infectious respiratory aerosols will be classified into:
• Droplets: Respiratory aerosols > 5 µm in diameter.
• Droplet nuclei: Respiratory aerosols ≤ 5 µm in diameter. the residue of dried respiratory aerosols (≤ 5 m in diameter) that results from evaporation of droplets coughed or sneezed into the atmosphere or by aerosolization of infective material.
A surgical or procedure mask protecting caregivers against droplet-transmitted pathogens and/or as part of facial protection for patient-care activities which are likely to generate splashes or sprays of blood, body fluids, secretions or excretions.
A room in which the air pressure differential between the room and the adjacent indoor airspace directs the air flowing into the room (i.e. room air is prevented from leaking out of the room and into adjacent areas such as the corridor).
A new strain of influenza virus that has not previously been circulating among human hosts. For example, avian influenza is an infection of birds caused by avian influenza viruses from one of the 16 type A subtypes. All birds are thought to be susceptible to infection with avian influenza viruses; certain avian influenza viruses (H5 and H7) may cause lethal outbreaks in poultry. Humans can occasionally be infected with avian influenza A viruses.
An epidemic occurring worldwide or over a very wide area, crossing boundaries of several countries, and usually affecting a large number of people.
Also known as a filtering face piece respirator, a particulate respirator is a type of mask that uses a filter as an integral part of the face piece or with the entire face piece composed of the filtering medium and a means of sealing to the face.
The practice of covering the mouth and nose during coughing or sneezing (using a medical mask, cloth mask, tissues, a sleeve or flexed elbow), followed by hand hygiene, to reduce the dispersal of respiratory secretions that may contain infectious particles.
Respiratory tract diseases are diseases that affect the air passages, including the nasal passages, the bronchi and the lungs. They range from acute infections, such as pneumonia and bronchitis, to chronic conditions such as asthma and chronic obstructive pulmonary disease.
A means of reducing the emission of droplets when a patient with ARD coughs or sneezes, such as covering of mouth and nose with hands or other materials (e.g. tissues, handkerchiefs, cloth masks, or medical masks), in order to reduce the dispersion of droplets from the infected/colonized patient. Hand hygiene should be performed immediately after contact with respiratory secretions.