No intervention will be administered in this arm. Investigators will give families a CO2 monitor to measure average CO2 levels in the home. Investigators will provide a link to the basic CDC isolation guidelines which would be part of standard of care. Investigators will test family members at day 0-1 for baseline testing; and again on day 7 for assessing secondary transmission among susceptible contacts.

Families are provided with one filtration fan unit per room in their home (and one for the index case; if the family lives in a studio, they would receive 2 units). Investigators will advise families on ventilation improvements in their home. Investigators will provide an instructional pamphlet that describes how the fans work and the importance of ventilation. Investigators will follow-up on day 3-4 to check in and run through a checklist to ensure the fans are working and ventilation improvements are being attempted. Investigators will give families a CO2 monitor to measure average CO2 levels in the home. Investigators will test family members at day 0-1 for baseline testing; and again on day 7 for assessing secondary transmission among susceptible contacts.

Investigators are using box fans with attached MERV16 filters, a design that has been tested and published in the scientific literature.

Investigators will measure the incidence of Covid19 in susceptible contacts on day 7.

Investigators will measure reported new upper respiratory symptoms in susceptible contacts.