WHO has contributed to guidance on ventilation and air-conditioning systems in the context of COVID-19, available here. WHO works closely with the World Meteorological Organization Joint Office for Climate and Health and the United States National Oceanic and Atmospheric Administration (NOAA) through the Global Heat Health Information Network to develop and update this guidance.
Additional information is available in the WHO interim guidance on infection prevention and control (IPC) strategies during health care when coronavirus disease (COVID-19) is suspected or confirmed. This guidance is intended for health workers, including health-care managers and infection prevention and control teams at the facility level, but is also relevant for the national and district/provincial levels.
In health facilities, large quantities of fresh and clean outdoor air are required to control contaminants and odours. There are three basic criteria for ventilation:
For health facilities in general, where aerosol generating procedures are not performed, ventilation of 60 litres/second per patient (L/s/patient) is adequate for naturally-ventilated areas, or 6 air changes per hour for mechanically-ventilated areas.
For areas where aerosol generating procedures are performed, recommended ventilation rates are as follows:
Air from the facility/area or patient room can be exhausted directly to the outdoors, where droplet nuclei will be diluted in the outdoor air, or passed internally through a special HEPA filter that removes most (99.97%) of droplet nuclei (aerosols) before it is returned to general circulation. If a HEPA filter is not used, the air should be exhausted directly to the outside away from air-intake vents, people and animals.
Some health facilities may use heating, ventilation and air-conditioning (HVAC) systems to maintain indoor air temperature and humidity at healthy and comfortable levels for staff, patients and visitors. A well-maintained and operated system may reduce the risk of transmission in indoor spaces by increasing the rate of air change, reducing recirculation of air and increasing the use of outdoor air.
HVAC systems should be regularly inspected, maintained, and cleaned. Rigorous standards for installation and maintenance of ventilation systems are essential to ensure that they are effective and contribute to a safe environment within the health facility as a whole.
In health facilities, use of desk or pedestal fans for air circulation should be avoided if possible unless it is in a single occupancy room when there are no visitors or staff present. If the use of desk or pedestal fans is unavoidable, ensure that the fan is directed away from the corridor or any area where people may pass by since the unfiltered air could potentially expose a passerby to the COVID-19 virus. In addition, outdoor air exchange should be increased by opening windows when fans are used.
The use of ceiling fans can improve circulation of outside air and avoid pockets of stagnant air in occupied space. However, it is critical to maintain good outdoor ventilation when using ceiling fans. An efficient way to increase outdoor air exchange is by opening windows. However, doors should be closed to avoid air from COVID-19 patient rooms to other areas in the health facility.
Some medical procedures can generate infectious aerosols and have been associated with a higher risk of transmission of coronaviruses (MERS-CoV, SARS-CoV-1, and SARS-CoV-2). Although there is no comprehensive list of aerosol-generating procedures, current data suggest that the following procedures can generate infectious aerosols:
It is not yet known whether aerosols generated by nebulizer therapy or high-flow oxygen delivery are infectious, as data on this is still limited.