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Wearing face masks at home, opening windows and frequently disinfecting surfaces are key to stopping the spread of Covid-19 in the home, a new study has found.

Researchers questioned 460 people from 124 families in Beijing on their household hygiene and behaviours during the pandemic. It’s thought most of the person-to-person transmission of Covid-19 in China occurred in families.

Each family had at least one confirmed case of Covid-19 between February and March. The average family size was four, but ranged from two to nine people, and was usually made up of three generations.

Researchers wanted to know what factors might increase or decrease the risk of catching the virus within the incubation period – 14 days from the start of the infected person’s symptoms.

Secondary transmission – where the virus 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. A third of the children caught the virus, compared with more than two thirds of the adults.

What reduced infection risk?

Opening windows and keeping at least one metre apart was associated with a lower risk of passing on the virus, even in more crowded households.

Frequent use of bleach or disinfectants for household cleaning and wearing a face mask at home before symptoms emerged – including by the first person to have them – were also associated with a reduced risk of transmission.

A face mask worn before symptoms started was 79% effective, and disinfection 77% effective, at stopping the virus from being passed on.

The World Health Organisation (WHO) and Public Health England (PHE) haven’t endorsed people wearing face masks indoors or outdoors, on the grounds that there’s little good quality evidence to warrant recommending this.

That said, Public Health England (PHE) does recommend face masks should be used by people with symptoms of coronavirus. However, with a third of people predicted to being asymptomatic, the researchers believe wearing a face mask in the home, full stop, may reduce the spread.

The UK government has recommended the use of face covers (not masks) when people visit public places where social distancing is hard to do. 

What increased infection risk?

Diarrhoea in the first person to become infected and close daily contact with family members increased the risk of passing on the virus. Diarrhoea was associated with a quadrupling in risk.

Close daily contact, such as eating meals around a table or watching TV together, was associated with an 18-fold increased risk of catching the virus.

So, what did the researchers conclude?

The study confirms that precautionary non-pharmaceutical interventions, such as mask use, disinfection and social distancing in households, “can prevent Covid-19 transmission during the pandemic, independent of household size or crowding”.

“Household transmission is a major driver of epidemic growth,” the researchers added.

The findings may be relevant for families living with someone in quarantine or in enforced social isolation – or for the families of health workers who may face an ongoing risk of infection, they said.