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New clues about the household spread of Covid-19

A recent study led by Imperial College London (ICL) that examined 279 households in London during the alpha and pre-alpha Covid-19 waves (August 1, 2020 to March 31, 2021) has provided the first empirical evidence for the transmission of SARS-CoV-2 via people’s hands and frequently touched surfaces in households, where most transmission of the coronavirus occurs. These findings support the use of frequent handwashing, regular surface disinfection, physical distancing, and mask wearing to mitigate the spread of Covid-19. 

“There’s no doubt that if you have Covid-19 you’re emitting the virus into the air as micro-aerosols as well as large droplets that land on your hands and the surfaces around you. What hasn’t been shown, until now, is that the presence of the virus on people’s hands or household surfaces predicts transmission to contacts,” said senior author Ajit Lalvani, an expert in Infectious Diseases at ICL.

“Our real-life study in London households provides the first empirical evidence to show that the presence of SARS-CoV-2 on people’s hands and surfaces contributes significantly to spread of Covid-19. Since we didn’t systematically sample household air, we cannot rule out airborne transmission occurring in parallel.”

All contacts of the infected study participants were regularly tested for Covid-19 and the scientists took swabs from primary cases’ and contacts’ hands, as well as the most frequently touched surfaces in households, such as fridge doors, kettle handles, or kitchen taps, to examine the correlations between microbiological detection of the virus on the hands and surfaces and transmission to household contacts.

 “In houses in which we found the virus on surfaces and the hands of participants, infection among contacts, and thus transmission, was significantly higher,” reported lead author Nieves Derqui, a PhD student in Epidemiology, Evolution, and Control of Infectious Diseases at ICL.

For instance, if the virus was detected on primary cases’ hands, contacts in their households were 1.7 times more likely to get infected than those in households where primary cases did not have the virus on their hands, and if the virus was detected on frequently touched surfaces, contacts were 3.8 times more likely to have detectable virus particles on their hands and 1.7 more likely to be infected.

“Our new understanding of the pathways of household transmission now enables us to prioritize simple measures to interrupt spread of the virus. Our data strongly suggest that as well as frequent handwashing, decontamination of frequently touched surfaces could prevent transmission,” Lalvani concluded.

The study is published in the journal The Lancet Microbe. 

By Andrei Ionescu, Staff Writer

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