How #Covid Spreads Within Households

The wearing of face masks and ventilation plays a major role in limiting the spread of the Covid-19 virus in public and crowded places.

hand sanitiser at the Balfour Hospital in 2020
Hand sanitiser station at Balfour Hospital in 2020 Image credit Nick Morrison

However, it is within households that the virus is able to spread most effectively.

Research by scientists at Imperial College London and published in  The Lancet Microbe has shown that preventing the spread of the virus within the home requires regular cleaning of surfaces and hands.

Professor Ajit Lalvani, and Director of NIHR HPRU in Respiratory Infections, explained:

“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.

“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.”

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.

Similarly, the presence of virus on primary cases’ hands was associated with a three times greater risk of contacts in the household having a positive hand-swab, and in turn, contacts with the virus on their hands were twice as likely to become infected with COVID-19.

If virus was present on frequently touched surfaces in the household, contacts were 3.8 times more likely to have detectable virus on their hands and 1.7 times more likely to be infected, i.e. to have a PCR-positive URT-swab.

Among the contacts who were initially uninfected but became infected with COVID-19 during the study, six had positive hand or household surface swabs prior to becoming infected. This supports the directionality of transmission being from household surfaces and contacts’ hands to their nose and throat.

Professor Lalvani said:

“My team’s Herculean logistical undertaking during the challenging circumstances at the height of the pandemic in real-life households strongly supports the theory that SARS-CoV-2 transmission from contaminated surfaces and hands does occur in households. With successive new variants likely to spread widely despite booster vaccinations, the simple, easily applicable public health interventions and messaging underpinned by our evidence are a valuable, risk-free and timely addition to the toolkit for living safely with COVID-19.

“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.”

It’s really that simple, clean surfaces and hands.

See also:

person in green button up shirt holding clear drinking glass
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3 replies »

  1. Thinking of the ads. on the telly – all those jolly gatherings…….

  2. The way in which this study has been reported on widely (unfortunately including here in the above article), I find very concerning because it leads us back to the old “sing Happy Birthday and wash your hands” mantra. And we all know that this focus on hands and fomites simply wasn’t enough because too long we had ignored the airborne route. Our infection rates and their consequences speak volumes that this was the case.
    I do not know where the in the above article cited statements of the authors come from. For me, it is far more relevant what they wrote (because this is what normally is reviewed by other experts as a safeguard and presents the facts) than what they said.
    It is easy to get carried away by enthusiasm when you speak about the results of your own research. This happens to students and experienced researchers alike and it is only human.
    But, simplified messages are problematic. Irrespectively, whether they come from a condensed interpretation from news outlets or from oral statements made by authors.

    I do agree with the in the original Lancet article far more nuanced worded concluding remarks:
    ‘Our results also have practical implications and support interventions such as frequent handwashing, surface cleansing, physical distancing, reducing direct contact, and use of masks to curb transmission in households’ and ‘the straightforward public health interventions and messaging underpinned by our evidence provide a timely, pragmatic component of the future toolkit for living safely with COVID-19.’

    It is noteworthy, that the authors see their evidence supporting a ‘component’ in the toolbox of NPIs, no more and no less.
    Hands and fomites do play a role in the transmission, obviously, as they do in many other infections, but I find it hard to believe that without examining the behavioural components (such as for example whether masks were worn in the home) and in the absence of air sampling any robust conclusions could be drawn. Personally, I believe that the study design was not ideal (possibly even flawed), although it did provide clues about the presence of viral material on hands of infected persons as well as on some surfaces.

    The only message which the results of this study should reinforce for the public is, in my opinion, that standard hand hygiene and surface cleaning remains relevant because it could still be a(nother) transmission route. But only in combination with other NPIs those measures contribute to reducing spread. On its own, hand and surface hygiene is unlikely to “prevent” transmission.

  3. It’s as though we’re living in different worlds.

    In one world – people are doing research into how Covid is transmitted, research in to Long Covid, etc.

    In a parallel world – most people are behaving as though Covid no longer exists.

    I feel we’re fighting a losing battle – but we’ll stick to our guns.

    I’m thinking of the last time I went to the hospital – there was a man in the waiting-room with a cold – coughing, making those noises people make when they have a bad cold. It did sound like ‘just’ a cold though, and he should have been at home, taking care of himself. Instead – sitting in the doctors waiting room – no mask – coughing his head off.

    I sat as far away from him as I could, but what about the next person to, unknowingly, sit in that chair?

    I hope the doctor gave him what-for – and didn’t catch anything from him.

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