Care homes: 1. =30 residents residing in single bedrooms* 2. Care homes that predominantly focus on care for older people (residential home/nursing home) 3. Willing to maintain a register of all residents, to be updated weekly until the end of February (after which new residents will not be invited) 4. Willing to invite residents to receive air filters and/or accept medical notes review until ten agree (“the ten”) per care home 5. Willing to provide anonymised resident infection data, administer brief resident and staff questionnaires, and respond to data queries 6. Care home owner permission to take part in the study 7. Willing to commit to installing air filters in the care home if allocated to the intervention group 8. Willing to commit to not installing air filters if allocated to control group Single bedrooms: residents residing in a room of single occupancy will be referred to as residents in a private and/or single bedroom. Residents may share bathroom facilities. All residents: 1. Expected to reside in the care home for at least 2 months of the care home data collection period Consented residents – ‘the ten’: The following eligibility criteria are for “the ten” residents invited to receive an air filter and/or permit medical notes review only: 1. In a single-occupancy bedroom 2. Expected to reside in the care home for at least 2 months of the care home data collection period 3. Able to give informed consent (or if lacks capacity, a consultee is willing to complete a consultee declaration form)

Care homes: 1. =30 residents residing in single bedrooms* 2. Care homes that predominantly focus on care for older people (residential home/nursing home) 3. Willing to maintain a register of all residents, to be updated weekly until the end of February (after which new residents will not be invited) 4. Willing to invite residents to receive air filters and/or accept medical notes review until ten agree (“the ten”) per care home 5. Willing to provide anonymised resident infection data, administer brief resident and staff questionnaires, and respond to data queries 6. Care home owner permission to take part in the study 7. Willing to commit to installing air filters in the care home if allocated to the intervention group 8. Willing to commit to not installing air filters if allocated to control group Single bedrooms: residents residing in a room of single occupancy will be referred to as residents in a private and/or single bedroom. Residents may share bathroom facilities. All residents: 1. Expected to reside in the care home for at least 2 months of the care home data collection period Consented residents – ‘the ten’: The following eligibility criteria are for “the ten” residents invited to receive an air filter and/or permit medical notes review only: 1. In a single-occupancy bedroom 2. Expected to reside in the care home for at least 2 months of the care home data collection period 3. Able to give informed consent (or if lacks capacity, a consultee is willing to complete a consultee declaration form)