TORONTO -- A new study has found that wearing a face mask in your home could help reduce the risk of spreading the coronavirus among those you live with.

Researchers from China, the U.S., and Australia carried out the retrospective cohort study between Feb. 28 and March 27, surveying 335 people from 124 families in Beijing, China, that had lived in the same house for at least four days prior and for more than a day after a person who had tested positive for COVID-19 started showing symptoms.

The researchers specifically focused on secondary cases of transmission of the virus, and how it spread in close contact situations, such as eating around a table or watching television, from someone in a household to other family members before the infected person became symptomatic.


Data was collected in three stages using a questionnaire that asked participants to share details about their living arrangements and self-report their practices around mask-wearing and physical distancing activities at home. The majority of participants ranged in age from 18 to 59, and about a quarter of them reported being over the age of 60. There were 13 children reported as secondary cases, with an average age of three years old.

Results of the study, published in the BMJ Global Journal on Thursday, concluded that wearing a face mask inside the home was 79 per cent effective in preventing transmission of COVID-19 between an infected person and other family members, but only before symptoms of the virus were present. It also found that the use of a face mask after symptoms of the coronavirus were present did little to provide additional protection.

When asked to clarify what kinds of masks were included in the research, one of the study’s authors and a professor of global biosecurity at the University of New South Wales, Raina MacIntyre, told in an email that participants wore surgical masks.

The study also found that daily disinfection habits in the household using chlorine or ethanol-based products also helped to curb transmission rates by 77 per cent. This was supported by another key finding in the study that showed the risk of close-contact transmission increased by four times if the infected person was experiencing diarrhea as a symptom. In the report, researchers said this finding established the importance of regularly cleaning the bathroom and toilet, as well as closing the toilet lid during flushing “to prevent the aerosolization of the virus.”


While the study may reinforce some key messaging public health officials in Canada and around the world have been giving around the use of face coverings to help limit the spread of COVID-19, Cynthia Carr, an epidemiologist and health policy expert with EPI Research Inc., says the biggest question she has with these findings is how achievable it will be for families to actually wear masks inside their homes and do so safely.

In Carr’s opinion, the feasibility and real-world applications of the study will depend on a number of factors. “I think we need to understand more about how long we have to wear the mask, given what we know about asymptomatic carriers,” Carr told in a phone interview from Winnipeg.

Whether young children and infants should wear masks and how to properly clean and maintain masks at home are other important questions Carr flagged, pointing out that most Canadians also don’t have easy access to surgical masks like people in countries like China do, where she says the practical use of face masks in daily life is much more established and accepted. “We’re still very much in the learning phase of wearing masks,” Carr added.

Carr also noted a critical shortage of personal protective equipment for front line health-care workers in Canada as another reason why an average family might not be able to access medical-grade face masks to protect against the virus.

But even with those concerns, Carr believes the study does well to serve as a reminder and enhances what the public is already being told about proper hygiene, disinfecting in the home, the use of masks and physical distancing. ”Masks do matter, and we should wear them in public. You should absolutely be wearing them if you’re living with someone, or taking care of someone who is infected,” Carr said. “It’s good to keep researching non-pharmaceutical options [for COVID-19], but we should keep a focus on hygiene, cleaning, and reducing our risk outside the home with masks and distancing,” she added.