London, Apr 30 (IANS): There is an important absence of evidence regarding the effectiveness of a potentially cost-efficient intervention, like air filters, to prevent indoor transmission of respiratory infections, including Covid-19, warns a study.

Controlling how we acquire and transmit respiratory infections is of huge importance, particularly within indoor environments such as care homes, households, schools/day care, office buildings and hospitals where people are in close contact.

"Whilst we found some evidence suggesting use of air filters could theoretically contribute to reducing the spread of Covid-19 and other respiratory infections by capturing airborne particles, there is a complete absence of evidence as to whether they actually reduce the incidence of these infections," said lead author Ashley Hammond, an Infectious Disease Epidemiologist at the Centre for Academic Primary Care, University of Bristol, in the paper published in the journal PLoS One.

Several manufacturers of portable air filters have claimed their products remove potentially harmful bacteria and viruses from indoor air, including Covid-19 viral particles. However, there is often no detailed evidence provided on their websites to corroborate their claims for potential consumers to review before purchasing.

A team of researchers from the Bristol University reviewed previous studies to investigate whether portable air filters used in any indoor setting can reduce incidence of respiratory infections. They also explored whether portable air filters in indoor settings capture airborne bacteria and viruses within them, and if so, what specifically is captured.

Two studies reported removal or capture of airborne bacteria in indoor settings (an office and emergency room), demonstrating that the filters did capture airborne bacteria and reduced the amount of airborne bacteria in the air. Neither tested for the presence of viruses in the filters, nor a reduction in viral particles in the air.