Reduction in Indoor Airborne Endotoxin Concentration by the Use of Air Purifier and Its Relationship with Respiratory Health: A Randomized Crossover Intervention Study

Endotoxins are biological components of particulate matter that cause adverse respiratory system effects. Recently, air purifiers have been widely used; however, their effects on endotoxins are not fully understood. We conducted a randomized crossover intervention study to evaluate the effects of air purifiers on indoor endotoxins and occupants’ respiratory health. Thirty-two healthy subjects were randomly assigned to two groups; each group spent four weeks using either a true or sham (filter removed) air purifier. Subsequently, the subjects spent an additional four weeks using the alternative air purifier. The indoor endotoxins in fine (PM2.5) and coarse (PM10–2.5) particulate matter were continuously collected, and pulmonary function was tested repeatedly during the study period. Household characteristics were assessed using a questionnaire. The geometric mean of the PM2.5 endotoxin concentrations was 0.13 EU/m3, which was significantly lower with true purifiers compared with sham purifiers, after adjusting for household characteristics (0.17 EU/m3). In addition, the PM2.5 endotoxin concentrations were significantly greater in reinforced concrete houses than in wooden houses. The PM10–2.5 endotoxin concentrations were significantly greater in homes with two or more household members, and in those with pets. No association was found between endotoxin concentration and respiratory health among the subjects.