air changes per hour

personal protective equipment

Special Administrative Region

severe acute respiratory disease

tuberculosis

World Health Organization

Set of managerial measures to warrant the needed conditions for the application of infection control principles in health care. These include establishment of sustainable infection control infrastructures and activities, clear policies on early recognition of infections, implementation of appropriate infection control measures, regular supplies and organization of services (e.g. creation of patient triage system and placement). The health-care facility management should also have staff planning to promote an adequate patient-to-staff ratio, provide staff training, and establish staff health programmes (e.g. vaccination, prophylaxis) to enhance the general health of the healthcare workers (WHO, 2007).

High-risk procedures that may increase the potential of generating droplet nuclei because of the mechanical force of the procedure (e.g. intubation, cardiopulmonary resuscitation, bronchoscopy, autopsy, and surgery where high-speed devices are used) (WHO, 2007).

A procedure that can induce the production of fine respiratory droplet in the patient.

A room with ≥12 air changes per hour (ACH) and controlled direction of air flow. 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. 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 (WHO, 2007).

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 and 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) (WHO, 2007).

For a positive pressure room — the ratio of the volume of outdoor air flowing into a given space in an hour divided by the volume of that space.

For a negative pressure room — the exhaust airflow rate is used for calculation.

A small room leading from a corridor into another room, often an isolation room.

A system where supplies and exhausts have been tested and adjusted to meet particular design specifications.

Dried-out residuals of droplets <5 μm in diameter.

Inspirable particles larger than 5 μm in diameter, which can be deposited on upper respiratory tract levels and mucosa.

Purpose-built openings in buildings for natural ventilation (e.g. windows, doors, solar chimneys, wind towers, trickle ventilators).

Outflow through unintended leakages in buildings.

A natural ventilation system that uses modern computer control systems, and may be assisted by mechanical ventilation systems.

Combination of both mechanical and natural ventilation (also called mixed-mode ventilation).

Air flow through unintended leakages into buildings.

See hybrid ventilation.

Use of natural forces to introduce and distribute outdoor air into or out of a building. These natural forces can be wind pressures or pressure generated by the density difference between indoor and outdoor air.

A mechanical ventilation system that uses an exhaust fan through which air is released.

The difference in air pressure between two areas. A room that is under negative pressure has a lower pressure than adjacent areas, which keeps air from flowing out of the room and into adjacent rooms or areas.

Transmission of droplet nuclei at short range during special circumstances, such as the performance of aerosol-generating procedures associated with pathogen transmission.

The ideal displacement in which ventilation air is pushed from one side of the room to the other without any recirculation and minimal air mixing. The piston ventilation system is the most efficient method of air exchange.

A mechanical ventilation system that uses a supply fan through which air is pushed into the room.

A quantity or an amount of particles.

The amount of the returned air (for recirculation). Although recirculated air can be filtered, its air quality is often worse than the outdoor air for most conventional applications. Therefore, filtered, recirculated air cannot replace outdoor air for ventilation.

Depending on the size of the particles (which range from large droplets to small droplet nuclei), respiratory droplets can be divided into large droplets, fine inhalable aerosols and droplet nuclei (see Annex C for more details).

The pattern of airflow that occurs when part of the air is stagnant in a ventilated room, and the ventilation air can bypass the stagnant air and move directly to the exhaust outlets.

A set of practices that apply to hospital inpatients with specific infections for which precautions beyond the standard precautions are needed to control infection in the health-care setting.

Ventilation provides outdoor air into a building or a room and distributes air within the building. The purpose of ventilation in buildings is to provide healthy air for breathing by diluting pollutants originating in the building with clean air, and by providing an airflow rate to change this air at a given rate. Ventilation is also used for odour control, containment control and climatic control (temperature and relative humidity).