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Study Backs Handwashing and Disinfecting to Cut COVID Transmission at Home

Scientists produced new evidence to support frequent handwashing and taking other precautions to prevent the spread of SARS-CoV-2 in what they said was a "pragmatic" part of a toolkit for living with COVID-19.

A study led by Imperial College London (ICL) offered real-world data to show how contamination of hands and surfaces with SARS-CoV-2 contributed significantly to the spread of COVID in people's homes.

Professor Ajit Lalvani, director of the NIHR Health Protection Research Unit in Respiratory Infections at ICL, who led the investigation, said: "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."

Study Involved Households in London

The longitudinal cohort study, published in The Lancet Microbe, was based on 414 susceptible household contacts, from 279 households with newly diagnosed primary cases, during the 'pre-alpha' wave of September to December 2020 and the B.1.1.7 'alpha' wave of December 2020 to April 2021.

Contacts were recruited regardless of symptom status and serially tested for SARS-CoV-2 infection by PCR testing and, in a sub-cohort of 134 individuals, by serial serology. Hands and frequently touched household surfaces were tested for the presence of SARS-CoV-2 as well as the number of virus particles. 

Household infection rate was 51∙8% in the full household contacts cohort and 73∙5% in the serology sub cohort for contacts exposed to alpha variant-infected primary cases.

After accounting for other potentially influential factors such as sex, vaccination status, underlying illnesses, and contacts' relationship to the primary case, the researchers found that if the virus was detected on primary cases’ hands, then contacts in their household were 1.7 times more likely to get infected than those in households where primary cases did not have the virus on their hands. If SARS-CoV-2 was present on household surfaces, such as fridge doors, handles, and taps, contacts were 3.8 times more likely to have detectable virus on their hands.

Contacts' risk of infection increased with a closer relationship to the primary case, with the household infection rate ranging from 16∙9% for non-related housemates to 48∙8% for partners of primary cases or bedroom-sharing relatives.

'First Real-world Evidence'

The study team, that included the UK Health Security Agency and the University of Oxford, said they had provided "the first empirical evidence to correlate presence of SARS-CoV-2 on candidate vectors with risk of infection in household contacts". 

However, they cautioned that the results might not translate to all variants of the SARS-CoV-2 virus, including the more stable Omicron variant, and that non-white ethnicities and older age groups were under-represented in the study.

Prof Lalvani said: "Our new understanding of the pathways of household transmission now enables us to prioritise 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."

This study was supported by the NIHR Health Protection Research Units in Respiratory Infections, in partnership with the UK Health Security Agency. NMF reports grants from the UK Medical Research Council, UK National Institute of Health and Care Research, UK Research and Innovation, Community Jameel, Janssen Pharmaceuticals, Bill & Melinda Gates Foundation, and Gavi, the Vaccine Alliance; consulting fees from the World Bank; payment or honoraria from the Wellcome Trust; travel expenses from WHO; advisory board participation for Takeda; and is a senior editor of the eLife journal. All other authors declare no competing interests.