Using Ventilation and filtration to reduce aerosol transmission of COVID-19 in long-term care homes

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In Canada and worldwide, COVID-19 has disproportionately affected residents and staff in long-term care homes (LTCH). Interim guidance on infection prevention and control (IPC) for COVID-19 within LTCHs has been developed to protect LTCH staff and residents. The following guidance on ventilation aims to potentially reduce the risk of COVID-19 transmission within LTCHs and, should be used jointly with the LTCH IPC guidance, not as a replacement. It is important to recognize that although ventilation is an important part of an overall strategy aimed to reduce the risks of COVID-19 transmission, ventilation is not likely to reduce transmission between individuals in close proximity, which is the predominant mode. Individuals who are physically near a person who is infected remain at risk from both droplet and aerosol transmission. This is due to their close proximity to the person who is infected.

The recommendations below are intended for LTCH managers and maintenance personnel. They are meant to complement other recommendations and guidance from public health authorities. The content may be adapted to other settings as appropriate (i.e., retirement homes, elder lodges) and its application may vary depending on the age of the building, building ventilation characteristics, and other factors.

Canadian public health guidance related to COVID-19 has evolved as our understanding of COVID-19 improves. We continually review the evidence as it's produced and work with our partners across the country and around the world to integrate the most up to date and highest quality information into our guidance.

Recommendations for long-term care homes

Assemble an interdisciplinary team to review the ventilation configuration of your facility. Include people with the following expertise that have knowledge of the specific LTCH: Heating, ventilating and air conditioning (HVAC) engineering; Building automation systems (BAS); Infection prevention and control; Administration; Occupational health and safety; and Nursing/clinical practice.

The LTCH administration should implement federal, provincial/territorial or regional infection prevention and control guidance for COVID-19 and best practices for long-term care, which includes outbreak management.

Consult the guidance for essential and general visitors applicable in your jurisdiction.

Ventilation and filtration considerations

Ensure administration and maintenance staff have a good understanding of the design and operation of the building ventilation system, with the system manual available for review. In consultation with an HVAC professional, ensure that your ventilation and filtration systems are properly installed, regularly inspected and maintained. HVAC professionals can measure airflows and other system parameters to ensure that these systems meet, and are running to, design specifications. Always consult an HVAC professional before making any modifications to the HVAC system as these can affect air distribution within the building, cause leakage around HVAC filters, and possibly lead to infiltration of pollutants into the building. HVAC professionals will be able to determine the need to increase the amount of air being delivered to occupied spaces by opening dampers, adding mechanical ventilation equipment (e.g., inline fans) or otherwise modifying airflow. All dampers should be routinely checked for proper operation, and BAS sensors, settings and indicators should be periodically checked against actual conditions in the field.

To improve ventilation, increase the outdoor air intake of the HVAC system to the greatest extent possible, given the system specifications for temperature and relative humidity. Increase the run time of forced-air ventilation systems to filter the air, and increase the dilution of indoor aerosols by drawing in outdoor air and exhausting contaminated indoor air. If the location of outdoor exhaust vents poses a concern given proximity to other spaces (e.g., balconies, patios, smoking areas), close off access to these areas. In consultation with an HVAC professional, minimize or avoid air recirculation through the ventilation systems, if possible.

In consultation with an HVAC professional and according to system specifications, consider using the highest efficiency particulate filter that the HVAC system is capable of handling without impeding airflows. Select a filter with a minimum efficiency reporting value (MERV) of 13 or higher, where possible. These filters capture particulates, including those containing infectious virus, if present. These filters can also reduce particulate pollutants from both indoor and outdoor sources. Ensure that the filters are well seated in their frame, so that air does not bypass the filter. Maintain a schedule for replacement of the HVAC filters, for example, replacing pre-filters every three months and main filters every six months, or as otherwise recommended by the filter supplier, making sure to wear appropriate personal protective equipment when changing filters.

Ensure that each room has adequate air changes. Pressure differentials and directional airflow are important for controlling the movement of air between zones in a building, and may be used to protect residents from being exposed to infectious aerosols. Refer to resources from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) for further information. In addition, consider increasing air exchange rates in the rooms of infected individuals, using only exhaust flow, if possible, as not to contaminate other areas. Check with an HVAC professional to determine if exhaust rates can be increased, ensuring rebalancing if modifying airflows. Prior to re-occupying a room, leave sufficient time to ensure that the air in the vacated room has been refreshed, making use of forced air (HVAC) systems, and potentially opening windows or running portable high efficiency particulate air (HEPA) units.

Take advantage of natural ventilation by opening windows, depending on outdoor weather and temperature. Opening multiple windows can increase ventilation by promoting a cross-breeze through a room. Before using natural ventilation, consult with an HVAC professional to ensure that doing so will not negatively affect the efficient operation of the HVAC system, or indoor humidity levels. Also, check that there are no air pollution advisories in your area, and that allergens are at safe levels for occupants. Make sure that opening windows and doors does not pose a security or safety risk (e.g., from falling). During extreme heat events, ensure that natural ventilation does not increase risks related to heat exposure.

Utilize zone controls to enhance ventilation in select areas, such as those with higher occupancy, and to minimize the extent that potentially contaminated air is being recirculated (e.g., ensure that contaminated air is not being drawn into air return vents for recirculation, if possible). In warm weather, use central air conditioning, while minimizing recirculation, and incorporating air filtration, if possible. If stand-alone air conditioning units are needed, aim the air stream to avoid blowing directly at or between people in the room, which can increase the risk of infection.

In addition to the above considerations, ensure that all plumbing traps remain full at all times to reduce the possibility of contaminants being passed through shared drainage systems that become dried out from lack of use (i.e., floor drains).

Options if ventilation cannot be improved

Portable or ceiling fans, or single unit air conditioners may circulate air within the room, but they do not exchange air. The use of localized fans or single unit air conditioners should be limited as they can propel infectious aerosols far away from their source and can direct virus-laden air towards residents, increasing infection risk. These types of devices are difficult to decontaminate and can be further sources of transmission. If using these units, aim the air stream to avoid blowing directly at or between people in the room.

High-quality HEPA filters are effective in capturing airborne particles, including some viruses. To date, there is no direct evidence that portable HEPA air cleaners are effective in reducing SARS-CoV-2 transmission in closed spaces. As such, they should not be seen as a replacement for adequate ventilation, physical distancing and hygienic measures, but could be considered as an additional protection in situations where enhancing natural or mechanical ventilation is not possible and in rooms that are not crowded. Even when a portable air cleaner is being used, it is still important that interactions between individuals are as few, as brief, and occur from the greatest physical distance, as possible. To maximize efficiency, portable air cleaners should be run continuously, and positioned to allow unimpeded airflow. Position the air cleaner to avoid blowing directly at or between people in the room, which may increase infection risk. Ensure the device's air intake is unobstructed by furniture or walls.

When purchasing portable air cleaners, make sure to look for certification by a recognized body such as the Association of Home Appliance Manufacturers (AHAM). Select an air cleaner with a clean air delivery rate (CADR) that is high enough for the room where it will be located. Follow the manufacturer's recommendations for operating, maintaining and cleaning the unit, and ensure filters are replaced regularly and as per manufacturer's instructions. Some portable air cleaners can produce by-products that are a health hazard. In particular, ozone producing air cleaners should be avoided.

Other ventilation appliances may be used to improve indoor air quality, such as heat recovery ventilation (HRV) and energy recovery ventilation (ERV) systems. HRV systems exchange stale indoor air for outdoor air while transferring the heat between the expelled indoor air to the incoming outdoor air. In cooler weather the heat is retained in the home, while in the warmer months the heat is expelled outside. This improves indoor ventilation while maintaining energy efficiency. ERVs transfer humidity, in addition to heat. Check that HRVs and ERVs are properly installed, maintained, and operational. Other than for servicing, your HRV or ERV should be running continuously and at the highest settings for fresh air ventilation.

In winter, air humidifiers may be used to increase the relative humidity level, which is often too low during the winter season. Air humidification and de-humidification systems are sometimes integrated into the HVAC system, and should be inspected, along with humidity sensors, as part of general HVAC maintenance. While humidifiers do not remove SARS-CoV-2 virus from the indoor air environment, relative humidity may impact the duration that particles that contain virus are suspended in the air, and how long they remain infectious. It is therefore important to maintain an optimal humidity level, between 40% and 60% in indoor settings. Lower humidity levels can cause droplets to shrink, and smaller particles (e.g., aerosols) can stay suspended in the air for longer. However, increasing humidity too much can lead to condensation on surfaces, as well as inside walls and building areas where it cannot be seen. This can lead to mould growth and the proliferation of mites. For more information, see the Health Canada Factsheet: Relative humidity indoors.

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