Covid-19 Spreads In Households Through SARS-CoV-2 On Hands, Surfaces: First-Of-Its-Kind Study

The study is the first to link the presence of SARS-CoV-2 on people's hands and frequently touched household surfaces to the risk of infection among contacts. 

The study authors have suggested that when someone in a household has Covid-19, other members should frequently wash their hands, disinfect surfaces regularly, maintain 'physical distancing', and wear masks, to prevent the spread of SARS-CoV-2. 

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Covid-19 is known to spread through aerosols and large droplets in the air, but the risk of fomite-borne transmission is generally considered to be low, according to the Centers for Disease Control and Prevention. Now, a new study has provided the first empirical evidence for the transmission of SARS-CoV-2, the causative organism of Covid-19, in households through people's hands and frequently touched surfaces.

The study, led by Imperial College London, was recently published in the journal The Lancet Microbe. 

What makes study a first-of-its-kind?

The highest transmission of SARS-CoV-2 occurs in households. The study, which sheds new light on the spread of Covid-19 in households, is the first to link the presence of SARS-CoV-2 on people's hands and frequently touched household surfaces to the risk of infection among contacts. 

The study authors have suggested that when someone in a household has Covid-19, other members should frequently wash their hands, disinfect surfaces regularly, maintain 'physical distancing', and wear masks, to prevent the spread of SARS-CoV-2. 

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How the study was conducted

As part of the study, the researchers analysed 279 households. The study was conducted at the height of the Covid-19 pandemic during the alpha and pre-alpha waves.

In a statement released by Imperial College London, Professor Ajit Lalvani, who led the research, and is the Director of the National Institute of Health and Care Research (NIHR) Health Protection Research Unit (HPRU) in Respiratory Infections, a research partnership between Imperial College London and the United Kingdom Health Security Agency (UKHSA), said there is no doing that if one has Covid-19, they are emitting SARS-CoV-2 into the air as micro-aerosols as well as large droplets that land on their hands and the surfaces around them. However, it had not been shown, until now, that the presence of SARS-CoV-2 on people's hands or household surfaces predicts transmission of Covid-19 to contacts. 

Lalvani explained that the 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 the spread of Covid-19. He said that since the researchers did not systematically sample household air, they cannot rule out airborne transmission occurring in parallel. 

Study was conducted early in the pandemic

The first-of-its-kind study recruited 414 susceptible household contacts living in the same households where a person was infected. Each household had one person who was infected with Covid-19 for the first time, at any time between August 1, 2020, and March 31, 2021. 

The study was conducted early in the pandemic, a time when very few people were vaccinated or previously infected. As a result, the majority were non-immune and susceptible to infection. This allowed the researchers to carefully assess risk factors and vectors for transmission in unique circumstances similar to a natural experiment. The study participants belonged to the age group of six to 79 years, and 52 per cent of them were female.

Swabs of primary cases, household contacts, frequently touched surfaces collected

The researchers regularly tested all the household contacts for SARS-CoV-2 infection through PCR (polymerase chain reaction) on nose and throat (upper respiratory tract) swabs. 

The study authors also collected swabs from the hands of the primary cases and household contacts, and also the most frequently touched surfaces in communal areas such as fridge-door and kettle handles, and kitchen taps. After collecting the swabs, the researchers measured SARS-CoV-2 genetic material (RNA) and the number of virus particles, and looked for correlations between microbiological detection of the virus on hands and surfaces and transmission to household contacts. 

Nieves Derqui, the first author on the paper, said that in the houses in which the researchers found the virus on surfaces and hands of participants, infection among contacts, and hence, transmission, was significantly higher.

Risk of Covid-19 infection among contacts in households where primary cases had SARS-CoV-2 on hands

The study accounted for other potentially influencing factors such as sex, vaccination status, underlying illnesses and contacts' relationship to the primary case, and found that if the virus was detected on the hands of the primary cases, then the contacts in their household were 1.7 times more likely to get infected than the contacts in households where primary cases did not have the SARS-CoV-2 on their hands. 

Risk of Covid-19 infection among contacts with SARS-CoV-2 on hands

According to the study, the presence of SARS-CoV-2 on the hands of primary cases was associated with a three times greater risk of contacts in the households having a positive hand-swab. 

Also, the presence of SARS-CoV-2 on the hands of contacts was linked with a two times greater risk of them becoming infected with Covid-19. 

Risk of Covid-19 infection among contacts in households where SARS-CoV-2 was detected on frequently touched surfaces

When SARS-CoV-2 was present on frequently touched surfaces in the household, the contacts were 3.8 times more likely to have detectable SARS-CoV-2 on their hands, and 1.7 times more likely to be infected. 

The study said that among the contacts who were initially uninfected but became infected during the study, six had positive hand or household surface swabs before becoming infected, implying that transmission could occur from household surfaces and the hands of contacts to their nose and throat. 

The researchers conducted whole genome sequencing of 25 primary cases and their respective contacts where this was possible, and confirmed that each primary case-contact pair was infected with the same SARS-CoV-2 strain. This confirmed household transmission between primary cases and their respective contacts. 

Significance of the study

Therefore, the study, through empirical evidence, strongly supports the fact that SARS-CoV-2 transmission from contaminated surfaces and hands does occur in households. The authors suggested frequent handwashing and decontamination of frequently touched household surfaces to prevent SARS-CoV-2 transmission. 

However, the authors noted that the study is observational, and cannot prove such causation.