Particle Air Cleaning and Respiratory Infections

Common communicable respiratory diseases, such as common colds and influenza, are transmitted indoors, in part, due to inhalation of small airborne particles containing viruses or bacteria produced during coughing, sneezing, and talking. The portion of total disease transmission that occurs via this mechanism is uncertain and a subject of debate. Tuberculosis and measles are other respiratory diseases common in many parts of the developing world and transmitted, at least in part, via infectious aerosols. Particle filtration systems can reduce indoor airborne concentrations of these particles; thus, filtration may decrease the incidence of the associated communicable respiratory infections. No published studies were identified that investigated whether particle filtration, or improvements in particle filtration, outside of health care facilities, reduced communicable respiratory infections.

Data from health care facilities have often involved highly susceptible subjects, such as those with compromised immune systems, and infections associated with surgeries or other medical procedures, thus, these data are not necessary applicable to other buildings. The results of modeling applicable to buildings outside of the health care sector suggest that having filters in heating, ventilating, and air conditioning systems, relative to having no filters, will substantially decrease the portion of disease transmission caused by these small particles [1]. Because most of the particles containing viruses and bacteria are not exceedingly small, they can be removed with filters having a moderate efficiency rating almost as well as they are removed by high efficiency filters. Increasing the filter efficiency above that of a moderate efficiency filter is predicted to provide minimal additional reduction in respiratory infection. However, the model inputs and model have a high level of uncertainty and experimental data are not available to confirm the model predictions. 

1.Stevens, B., HVAC filtration and the Wells-Riley approach to assessing risks of infectious airborne diseases. 2012, Illinois Institute of Technology: Chicago, IL Available from: https://www.nafahq.org/wp-content/uploads/WellsRileyReport.pdf.