Should homes and workplaces purchase portable air filters to reduce the transmission of SARS-CoV-2 and other respiratory infections? A systematic review.

Daniel Dunea,Alastair D Hay,Ashley Hammond,Claire A Woodall,Hannah V Thornton,Tanzeela Khalid

doi:10.1371/journal.pone.0251049

Daniel Dunea, Alastair D Hay + Show 4 more

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https://doi.org/10.1371/journal.pone.0251049

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Abstract

Respiratory infections, including SARS-CoV-2, are spread via inhalation or ingestion of airborne pathogens. Airborne transmission is difficult to control, particularly indoors. Manufacturers of high efficiency particulate air (HEPA) filters claim they remove almost all small particles including airborne bacteria and viruses. This study investigates whether modern portable, commercially available air filters reduce the incidence of respiratory infections and/or remove bacteria and viruses from indoor air. We systematically searched Medline, Embase and Cochrane for studies published between January 2000 and September 2020. Studies were eligible for inclusion if they included a portable, commercially available air filter in any indoor setting including care homes, schools or healthcare settings, investigating either associations with incidence of respiratory infections or removal and/or capture of aerosolised bacteria and viruses from the air within the filters. Dual data screening and extraction with narrative synthesis. No studies were found investigating the effects of air filters on the incidence of respiratory infections. Two studies investigated bacterial capture within filters and bacterial load in indoor air. One reported higher numbers of viable bacteria in the HEPA filter than in floor dust samples. The other reported HEPA filtration combined with ultraviolet light reduced bacterial load in the air by 41% (sampling time not reported). Neither paper investigated effects on viruses. There is an important absence of evidence regarding the effectiveness of a potentially cost-efficient intervention for indoor transmission of respiratory infections, including SARS-CoV-2. Two studies provide 'proof of principle' that air filters can capture airborne bacteria in an indoor setting. Randomised controlled trials are urgently needed to investigate effects of portable HEPA filters on incidence of respiratory infections.

Highlights

Respiratory infections such as coughs, colds, and influenza, are common in all age groups, and can be either viral or bacterial
16 were excluded for the following reasons: ten studies did not use portable filters, three studies were conducted in experimental germ-free chambers only and not identified as commercially available filters, two studies did not report any data on the functionality of the air filters, and one study was conducted in an aircraft
Despite finding very few studies, we adopted a systematic approach with a broad search strategy, and are confident we captured all evidence regarding modern portable high efficiency particulate air (HEPA) filters currently available, including studies related to SARS-CoV-2, of which there were none

Summary

Introduction

Respiratory infections such as coughs, colds, and influenza, are common in all age groups, and can be either viral or bacterial. Viral dimensions range between 0 02–0 3μm, and bacteria 0 5– 10μm [1]. Bacteria and viruses can become airborne via talking, coughing or sneezing which generate aerosols (diameter up to 5μm) or droplets (diameter larger than 5μm) [2, 3]. Some of the most pathogenic viruses such as influenza, respiratory syncytial virus, adenovirus and coronavirus can be aerosolised [2]. There is evidence that respiratory pathogens are carried in aerosols, known as bioaerosols [1], and that vomiting can aerosolise norovirus [4]. Microbes may invade the respiratory or gastrointestinal mucosa, causing infection. Airborne particles may land on surfaces and hands, increasing the chance of direct and indirect transmission

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