Portable air cleaners and residential exposure to SARS-CoV-2 aerosols: A real-world study

Abstract

Individuals with COVID-19 who do not require hospitalization are instructed to self-isolate in their residences. Due to high secondary infection rates in household members, there is a need to understand airborne transmission of SARS-CoV-2 within residences. We report the first naturalistic intervention study suggesting a reduction of such transmission risk using portable air cleaners (PACs) with HEPA filters. Seventeen individuals with newly diagnosed COVID-19 infection completed this single-blind, crossover, randomized study. Total and size-fractionated aerosol samples were collected simultaneously in the self-isolation room with the PAC (primary) and another room (secondary) for two consecutive 24-h periods, one period with HEPA filtration and the other with the filter removed (sham). Seven out of sixteen (44%) air samples in primary rooms were positive for SARS-CoV-2 RNA during the sham period. With the PAC operated at its lowest setting (clean air delivery rate [CADR] = 263 cfm) to minimize noise, positive aerosol samples decreased to four out of sixteen residences (25%; p = 0.229). A slight decrease in positive aerosol samples was also observed in the secondary room. As the world confronts both new variants and limited vaccination rates, our study supports this practical intervention to reduce the presence of viral aerosols in a real-world setting.

Keywords: Air change rate; Airborne transmission; COVID-19 pandemic; COVID-19 symptoms; PTFE filter virus sampling; SARS-CoV-2 aerosols.

FIGURE 1

Flow diagram indicating the number of residents who participated in the single‐blind crossover randomized study; PAC, portable air cleaner

FIGURE 2

Ct values of SARS‐CoV‐2 genes detected in aerosol samples of seventeen residences: (A) primary room during the sham period with no HEPA filter in the PAC; (B) primary room during the filtration period with HEPA filter in the PAC; (C) secondary room during the sham period with no HEPA filter in the PAC; (D) secondary room during the filtration period with HEPA filter in the PAC. Black, orange, and blue bars represent the Ct values for N, ORF1ab, and S genes, respectively. NA (not applicable) refers to samples excluded due to technical malfunction; PAC, portable air cleaner

FIGURE 3

Association between SARS‐CoV‐2 RNA detection in saliva and aerosol (e.g., TSP) samples collected during the sham period (without HEPA filter in the portable air cleaner (PAC)). The clinical samples were stratified into two groups at the 25th percentile Ct values of N and ORF1ab genes: "Low Ct" which indicated higher viral load and "High Ct" which indicated lower viral load. (A) Aerosol samples collected in the primary room of 16 residences (saliva N gene 25th percentile Ct value 18.64; Saliva ORF1ab gene 25th percentile Ct value 18.29); (B) Aerosol samples collected in the secondary room of 15 residences (saliva N gene 25th percentile Ct value: 21.56; saliva ORF1ab gene 25th percentile Ct value: 21.36)

FIGURE 4

Association between SARS‐CoV‐2 RNA in aerosol (e.g., TSP) samples collected in the primary room during the sham period (without HEPA filter placed in the portable air cleaner (PAC)) and symptoms reported by the self‐isolating resident with COVID‐19. (A) Any one of the respiratory symptoms (e.g., cough/sore throat/shortness of breath) and (B) Any one of the following symptoms: fever or cough or sore throat. p‐values from Fisher's exact test are reported to associate the independent categorical variables