Summary
Background
Despite circumstantial evidence of SARS-CoV-2 spread by aerosols and fomites , empirical data linking either pathway to transmission is scarce. Here we aimed to evaluate whether the presence of SARS-CoV-2 on frequently touched surfaces and on residents’ hands was a predictor of household transmission of SARS-CoV-2.
Methods
In this longitudinal cohort study, during the pre-alpha (September to December 2020) and alpha (B.1.1.7; December 2020 to April 2021) SARS-CoV-2 variant waves, we prospectively recruited contacts from households exposed to newly diagnosed primary COVID-19 cases, in London, United Kingdom.
To maximally capture transmission events, contacts were recruited regardless of symptom status and serially tested for SARS-CoV-2 infection by RT-PCR in upper respiratory tract (URT) specimens and, in a subcohort, by serial serology. Hands of contacts, hands of primary cases, and samples from frequently touched surfaces from common areas were tested for SARS - CoV-2 RNA. SARS-CoV-2 URT isolates from 25 primary case-contact pairs underwent whole genome sequencing (WGS).
Results
From August 1, 2020 to March 31, 2021, 620 contacts of primary cases infected with SARS-CoV-2 confirmed by PCR were recruited. 414 household contacts (from 279 households) with serial URT PCR results available were analyzed in the complete household contacts cohort, and of these, 134 contacts with longitudinal serology data available and not vaccinated before enrollment were analyzed in the subcohort. of serology.
The household infection rate was 28.4% (95% CI: 20.8–37.5) for alpha-preexposed contacts and 51.8% (42.5–61.0) for those contacts exposed to alpha (p=0 ·0047). The URT RNA viral load of primary cases did not correlate with transmission, but was associated with the detection of SARS-CoV-2 RNA on their hands (p = 0.031).
SARS-CoV-2 detected on the hands of primary cases, in turn, predicted the risk of infection of contacts (adjusted relative risk [aRR] = 1·70 [95% CI 1·24–2·31] ), as well as the presence of SARS-CoV-2 RNA on household surfaces (aRR=1·66 [1·09–2·55]) and hands of contacts (aRR=2·06 [1·57–2 ·69]).
In six contacts with an initial negative URT PCR result, hand swab (n = 3) and household surface (n = 3) PCR positivity preceded URT PCR positivity. WGS corroborated household transmission.
Interpretation The presence of SARS-CoV-2 RNA on the hands of primary cases and contacts and on frequently touched household surfaces is associated with transmission, identifying them as potential vectors for spread in households. Our study provides the first empirical evidence to correlate the presence of SARS-CoV-2 in candidate vectors with risk of infection in household contacts. These findings from a real-world community setting substantially increase our understanding of household transmission of SARS-CoV-2, the setting for most transmissions globally. Our results also have practical implications and support interventions such as frequent handwashing, cleaning surfaces, physical distancing, reducing direct contact, and wearing masks to curb transmission in households. As governments around the world develop policies to manage successive new COVID-19 variants that are widely transmitted through vaccinated populations,10 alternative interventions are urgently needed to prevent transmission. Simple public health interventions and messages supported by our evidence provide a timely and pragmatic component of the future toolkit for living safely with COVID-19. |
Comments
A new study led by Imperial College of London provides the first empirical evidence of SARS-CoV-2 transmission through people’s hands and frequently touched household surfaces.
The research sheds new light on the spread of COVID-19 in homes, where most SARS-CoV-2 transmission occurs, and is the first to link the presence of SARS-CoV-2 on hands of people and frequently touched household surfaces with the risk of infection between contacts.
The findings support the use of at-home interventions when someone has an infection, particularly frequent handwashing, regular disinfection of surfaces and physical distancing, as well as the use of masks to slow the spread of COVID-19.
The study of 279 homes in London, published in The Lancet Microbe , was conducted at the height of the pandemic during the alpha and pre-alpha waves. The research was carried out at the Health Protection Research Unit (HPRU) of the National Institute for Health and Care Research (NIHR) in Respiratory Infections, a research partnership between Imperial College of London and the Safety Agency of the United Kingdom Health Authority (UKHSA).
Professor Ajit Lalvani, lead author of the study and NIHR HPRU director on respiratory infections, said: "There is no doubt that if you have COVID-19, you are emitting the virus into the air in the form of microaerosols and large droplets that land on your hands. "and on the surfaces around them. What has not been shown, until now, is that the presence of the virus on people’s hands or on household surfaces predicts transmission to contacts."
“Our real-life study in London homes provides the first empirical evidence showing that the presence of SARS-CoV-2 on people’s hands and surfaces contributes significantly to the spread of COVID-19. Since we do not systematically sample household air, we cannot rule out that airborne transmission occurs in parallel.”
The first study of its kind, conducted by researchers at Imperial College of London , UKHSA and the University of Oxford, prospectively recruited 414 susceptible household contacts living in the same households as 279 newly diagnosed primary cases between August 1, 2020 and on March 31, 2021. Since the study was conducted early in the pandemic, very few had been vaccinated or previously infected and therefore most were not immune and were susceptible to infection. This allowed researchers to rigorously evaluate risk factors and transmission vectors under unique circumstances similar to a natural experiment. The age range was 6 to 79 years, and 52% were women.
All contacts were regularly tested for SARS-CoV-2 infection using PCR on nose and throat (upper respiratory tract (URT)) swabs.
The researchers also took swabs from the hands of primary cases and contacts, as well as from frequently touched surfaces in common areas (e.g., refrigerator and kettle door handles, kitchen faucets , etc.). ) to measure the genetic material of SARS-CoV-2 (RNA) and the number of viral particles. The researchers looked for correlations between microbiological detection of the virus on hands and surfaces and transmission to household contacts.
Nieves Derqui, first author of the study, from the NIHR HPRU at Imperial College of London in Respiratory Infections, said: “In the homes where we found the virus on the surfaces and hands of the participants, infection between contacts and, therefore, Therefore, transmission was significantly higher.”
After taking into account other potentially influential factors, such as sex, vaccination status, underlying diseases, and the relationship of contacts to the main case, the researchers found that if the virus was detected on the hands of the main cases , contacts in their household were 1.7 times more likely to be infected than those in households where the primary cases did not have the virus on their hands.
Similarly, the presence of the virus on the hands of primary cases was associated with a three-fold increased risk of household contacts having a positive swab, and, in turn, contacts with the virus on their hands had the twice as likely to be infected with COVID-19.
If the virus was present on frequently touched surfaces in the home, 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., have a swab URT positive for PCR.
Among contacts who were initially uninfected but became infected with COVID-19 during the study, six had positive swabs from hands or household surfaces before becoming infected. This supports the directionality of transmission from household surfaces and contacts’ hands to the nose and throat.
Whole genome sequencing of the 25 primary cases and their respective contacts, where possible, confirmed that each pair of primary cases and contacts was infected with the same strain of SARS-CoV-2, confirming domestic transmission between the cases. primary and their respective contacts.
Professor Lalvani said: “ My team’s herculean logistical undertaking during the challenging circumstances at the height of the pandemic in real-life homes strongly supports the theory that transmission of SARS-CoV-2 from contaminated surfaces and hands It happens in homes . Given that successive new variants are likely to spread widely despite booster vaccinations, simple, easy-to-implement public health interventions and messages supported by our evidence are a valuable, risk-free and timely addition to the toolkit. to live safely with COVID-19.
"Our new understanding of household transmission pathways now allows us to prioritize simple measures to interrupt the spread of the virus. Our data strongly suggests that, in addition to frequent handwashing, decontamination of frequently touched surfaces could prevent infection." transmission ".
Despite the important findings, the researchers note that this is an observational study and, as such, cannot prove causality. Furthermore, since household air was not systematically sampled, airborne transmission cannot be ruled out .
They also acknowledge that non-white ethnicities and older age groups were underrepresented in the study and their results were limited to pre-alpha and alpha variants, so the results may not apply to other groups or more infectious variants. recent.
Implications of all available evidence
This study, to our knowledge, is the first to identify a correlation between SARS-CoV-2 RNA in candidate vectors and infection of contacts. These longitudinal empirical data from a real-world community setting substantially improve our understanding of the spread of SARS-CoV-2 in households, which is the setting for most transmissions globally . Our findings support interventions such as frequent handwashing, cleaning surfaces, physical distancing, reducing direct contact, and wearing masks to reduce transmission in households.
