In a new study, researchers found that wearing face masks at home might help ward off the spread of COVID-19 infection among family members living in the same household, but only before symptoms develop.
This practice was 79% effective at curbing transmission before symptoms emerged in the first person infected, but it wasn’t protective once symptoms had developed.
The research was conducted by a team at Beijing Normal University and elsewhere.
The figures in China suggest that most of the person to person transmission of SARS-CoV-2, the coronavirus responsible for COVID-19 infection, has occurred in families.
But it’s not clear if the wearing of face masks might help curb household transmission rates, along with social distancing and disinfection.
The World Health Organization (WHO) and Public Health England haven’t endorsed the wearing of face masks indoors or outdoors, on the grounds that there’s little good-quality evidence to warrant recommending this.
To explore whether face masks might make a difference, the researchers questioned 460 people from 124 families in Beijing, China, on their household hygiene and behaviors during the pandemic.
Each family had at least one laboratory-confirmed case of COVID-19 infection between late February and late March 2020.
The average family size was 4, but ranged from 2 to 9, and usually comprised three generations.
Family members were defined as those who had lived with the infected person for 4 days before and more than 24 hours after that person’s symptoms first appeared.
The researchers wanted to know what factors might heighten or lessen the risk of subsequently catching the virus within the incubation period—14 days from the start of that person’s symptoms.
During this time, secondary transmission—spread from the first infected person to other family members—occurred in 41 out of the 124 families.
A total of 77 adults and children were infected in this way, giving an ‘attack rate’ of 23% or around 1 in 4.
Around a third of the study, children caught the virus compared with more than two-thirds of the adults.
Twelve of the children had mild symptoms; one had none. Most (83%) of the adults had mild symptoms; in around 1 in 10, symptoms were severe, and one person became critically ill.
Daily use of disinfectants, window opening, and keep at least 1 meter apart were associated with a lower risk of passing on the virus, even in more crowded households.
But daily contact and the number of family members wearing a face mask after the start of symptoms in the first person to develop them were associated with a heightened risk.
Of all the behavioral and hygiene factors, four were significantly associated with the secondary transmission of the virus.
Diarrhea in the first person to become infected and close daily contact with them increased the risk of passing on the virus:
diarrhea was linked to a quadrupling in risk, while close daily contact, such as eating meals around a table or watching TV together, was associated with an 18-fold increased risk.
Frequent use of bleach or disinfectants for household cleaning and the wearing of a face mask at home before symptoms emerged, including by the first person to have them, was associated with a reduced risk of viral transmission.
A face mask worn before symptoms started was 79% effective, and disinfection 77% effective, at stopping the virus from being passed on.
The researchers suggest the findings back universal face mask use, not just in public spaces, but also at home.
And the findings may also be relevant for families living with someone in quarantine or in enforced social isolation, and for the families of health workers who may face an ongoing risk of infection.
The study is published in BMJ Global Health.
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