Researchers said that people who are at most risk should consider the measures to prevent passing on the disease to members of their household.
Professor Raina MacIntypre, head of the Biosecurity Research Programme, at the University of New South Wales, said: “I think in a community where there is a lot of infection, or where one family member is at high risk of infection, for example if they are a health worker working on a Covid-19 ward, it is possible to observe hygiene measures at home such as daily disinfection of commonly touched surfaces, wearing a mask and avoiding close contact.
“It may vary culturally, but it is possible, as shown in the study. The families which did not have onward infection observed these measures. Interestingly, household crowding did not increase risk if hygiene measures were followed.”
The World Health Organization (WHO) and Public Health England (PHE) still does not recommend the wearing of face masks indoors or outdoors, on the grounds that there is little good quality evidence to suggest it helps.
To determine whether face masks do make a difference, researchers questioned 460 people from 124 families in Beijing, China, on their household hygiene and behaviours during the pandemic.
Each household had at least one laboratory confirmed case of Covid-19 infection between late February and late March 202 and a secondary transmission spread to 77 other family members, occuring in 41 out of the 124 families.
The researchers wanted to know what factors might heighten or lessen the risk for people living alongside a person with the virus.
Diarrhoea was associated with a quadrupling in risk, while close daily contact, such as eating meals round a table or watching TV together, was associated with an 18-fold increased risk.
Frequent use of bleach lowered the risk by 77 per cent and a face mask by 79 per cent.
The researchers say the findings back universal face mask use, not just in public spaces, but also at home.
Commenting on the findings, Trish Greenhalgh Professor of Primary Health Care Services, at the University of Oxford, said: “Of all the measures tested, mask-wearing seemed the most effective. Disinfecting, opening windows and keeping one metre apart also seemed to help.
“The mask-wearing is perhaps the most interesting as it’s something that few people currently do in their own homes, especially when not symptomatic.
“The findings must be weighed against the practicalities and the absolute risks involved. In localities where the incidence of Covid-19 is high, people might feel this measure is worth the inconvenience, especially if there is a vulnerable family member.
“Where the incidence of the disease is low, the balance between benefits and hassles may lean more towards the latter.”