Efficacy of Portable Air Cleaners and Masking for Reducing Indoor Exposure to Simulated Exhaled SARS-CoV-2 Aerosols — United States, 2021

Abstract

Release on the MMWR website (https://www.cdc.gov/mmwr).SARS-CoV-2, the virus that causes COVID-19, can be spread by exposure to droplets and aerosols of respiratory fluids that are released by infected persons when they cough, sing, talk, or exhale. To reduce indoor transmission of SARS-CoV-2 between persons, CDC recommends measures including physical distancing, universal masking (the use of face masks in public places by everyone who is not fully vaccinated), and increased room ventilation (1). Ventilation systems can be supplemented with portable high efficiency particulate air (HEPA) cleaners* to reduce the number of infectious particles in the air and provide enhanced protection from transmission between persons (2); two recent reports found that HEPA air cleaners in classrooms could reduce overall aerosol particle concentrations by ≥80% within 30 minutes (3,4). To investigate the effectiveness of portable HEPA air cleaners and universal masking at reducing exposure to exhaled aerosol particles, the investigation team used respiratory simulators to mimic a person with COVID-19 and other, uninfected persons in a conference room. The addition of two HEPA air cleaners that met the Environmental Protection Agency (EPA)-recommended clean air delivery rate (CADR) (5) reduced overall exposure to simulated exhaled aerosol particles by up to 65% without universal masking. Without the HEPA air cleaners, universal masking reduced the combined mean aerosol concentration by 72%. The combination of the two HEPA air cleaners and universal masking reduced overall exposure by up to 90%. The HEPA air cleaners were most effective when they were close to the aerosol source. These findings suggest that portable HEPA air cleaners can reduce exposure to SARS-CoV-2 aerosols in indoor environments, with greater reductions in exposure occurring when used in combination with universal masking.A breathing aerosol source simulator was used to mimic a meeting participant exhaling infectious particles (source), and three breathing simulators were used to mimic a speaker and two participants exposed to these aerosol particles (receivers) (Figure 1). The methods used were similar to those used in previous studies of aerosol dispersion and transport in indoor spaces (3,4,6). The simulators were placed in a 584-ft 2 (54-m 2 ) * HEPA air cleaners consist of a filter capable of removing ≥99.97% of particles from the air and a fan or blower to draw air through the filter. HEPA air cleaners are commercially available, relatively inexpensive, and easy to use.

Airborne transmission of respiratory viruses

“…The WHO has recently recommended a ventilation rate of 10 liters per second per person (149). Proper placement of portable high-efficiency particulate air (HEPA) purifiers, which are capable of removing ≥99.97% of aerosol particles ≥0.3 mm, is also effective in reducing exposure of infectious aerosols, especially when combined with ventilation and universal masking (150)(151)(152). Although ventilation and filtration help to remove virus-laden aerosols, they must be implemented correctly to reduce the spread and risk of aerosol inhalation (93,151).…”

Guidance for Implementing COVID-19 Prevention Strategies in the Context of Varying Community Transmission Levels and Vaccination Coverage

“…No one strategy is sufficient to prevent transmission, and multiple interventions should be used concurrently to reduce the spread of disease ( 6 ). Proven effective strategies against SARS-CoV-2 transmission, beyond vaccination, include using masks consistently and correctly ( 7 , 8 ), maximizing ventilation both through dilution ( 9 , 10 ) and filtration ( 11 ) of air, and maintaining physical distance and avoiding crowds ( 12 , 13 ). Basic public health measures such as staying home when sick, handwashing, and regular cleaning of high-touch surfaces should also be encouraged.…”

School Operation for the 2021-2022 Academic Year in the Context of the COVID-19 Pandemic

“…The use of portable air cleaners with high efficiency particulate air (HEPA) filter units in classrooms may be considered in spaces/classrooms with limited ability to achieve adequate ventilation (i.e., unable to open windows, no/insufficient HVAC ventilation), taking into consideration the transmission risk (e.g., age, classroom activities, community epidemiology). [90][91][92] Commercially available air cleaners with HEPA filter units can provide supplemental filtration in an indoor space. 89,93 Portable air cleaners can also be constructed by attaching a MERV13 (or other high efficiency) filter to a box fan.…”