Evaluation of the effectiveness of air purification in reducing indoor air pollution and asthma deterioration in households with a member who has asthma: a randomized control trial.

The proposed study is a randomised placebo-controlled crossover trial Twenty households including at least one member with asthma will be recruited so that half of the households have actively used wood heaters and the other half have an electrical form of heating (e.g., reverse cycle/split system air conditioning). The households will be initially randomised into two groups (A- air purifiers with filters-intervention) & (B-air purifiers without filters-placebo) at a 1 (wood heater):1 (non-wood heater) ratio. After two weeks, the groups will be switched: Group A will have their active filter changed for a dummy filter, and Group B will have their dummy filter changed for an active filter. This will occur two more times so that each of the two groups experience two intervention periods (2 x 2 weeks) and two placebo periods (2 x 2 weeks). The study team will change the filter on the air cleaner in each participating household each fortnight, at the same time as the fortnightly visits. All households will have air quality measurements collected in the main living room or the room containing the wood heater. Both the participants and investigators will be blinded to the intervention assignment in each of the study-groups. To ensure that the study is double blind (and the air purifiers are indistinguishable from each other) someone unrelated to the study will install either a HEPA filter or blank cartridge in each purifier. The date and time the filter is changed will be recorded by the study team. The air quality monitoring will run continuously over the intervention period. Each household member will record in a daily diary the time spent at home. There is no minimum requirement for exposure to air purification to reflect the fact that this is a real-world intervention and as such the study team aims to replicate real world exposures.