The research exhibits that SARS-CoV-2 an infection is 4 instances extra prone to happen by way of family transmission than locally

A group of researchers from the USA, in collaboration with their Swiss colleagues, carried out a comprehensive population-based serological test to understand the transmission dynamics of Coronavirus 2 (SARS CoV-2) with Severe Acute Respiratory Syndrome – the novel causative agent of the Coronavirus Disease 2019 ( COVID-19).

Their study, entitled "Household Transfer of SARS-COV-2: Findings from a Population-Based Serological Assessment," is available on the preprint server website medRxiv. *

The background and need for the study

With a high rate of transmission between people, over 50 million people worldwide have been infected with SARS CoV-2 since it first appeared in Wuhan, China, in late December 2019.

People in household contact with an infected person therefore have a higher risk of contracting the virus. Studies of the transmission of the virus within household contacts are therefore critical to better understanding the transmission of COVID-19.

Currently, studies of COVID-19 transmission in the household depend on the detection of contact-based infections using reverse transcription polymerase chain reaction (RT-PCR) tests, a core-derived method used to detect the presence of SARS-CoV can. 2s genetic material in host cells. This is the most common form of testing currently and is usually done with nasal swabs. Currently, those who have been in contact with people who have shown mild or no symptoms may be overlooked in RT-PCR testing due to the limited window of time in which virological testing can give positive results. The study's authors explain that these limitations may underestimate the actual mild or asymptomatic cases among household contacts and may miscalculate household secondary attack rates.

Serological examinations

Serological tests look for antibodies to SARS-CoV-2 in a person's blood. The researchers suggest that this form of testing could be an effective alternative for determining the spread of the virus among household contacts. On the one hand, these serological tests provide positive results for an infected person over a longer period of time than the RT-PCR test.

A recent large meta-analysis of other studies has shown that the secondary attack rate in the home is around 17 percent. Studies have therefore overlooked various aspects of estimating household infection rates in order to close the knowledge gaps. This study was carried out with serological tests.

Frequency of households of different sizes in the study (A), proportion of seropositive by house size (B) and distribution of the number of seropositive persons in the household by size (C).

Importance of this study

This study was conducted to clarify the transferability of asymptomatic infections and infections from household and community contacts in patients with COVID-19. This would help understand and design ways to control the spread of the infection, the researchers wrote. Serological studies helped identify anyone previously infected, the team wrote.

Study design

This was the SEROCoV-POP study, a population-based study on people between the ages of 20 and 74 years from Geneva (canton), Switzerland.

All survey participants (10,587 in total) were invited to take part in the serological survey. Participants were asked to bring all members of their household over 5 years. Contacts inside and outside the household have been taken into account since January 2020.

All study participants and household contacts were asked about possible symptoms such as cough, fever, shortness of breath or loss of smell or taste since January 2020 up to 2 weeks before the serological blood test. Anti-SARS-CoV-2 IgG antibodies were detected for all participants using ELISA tests (Enzyme-Linked Immunosorbent Assay). The antibodies were against the S1 domain of the SARS-CoV-2 spike protein.

The team used chain binomial models to assess the number of infections prevalent in households and to estimate the risk of transmission within and outside of the household.

Results

Between April and June 2020, a total of 4,524 household members aged 5 and over from 2,267 households took part in this study. The mean age was 53 years and 53.6 percent of the participants were female. Overall results were:

  • The risk of infection from a single infected household contact was 17.2 percent (95% CrI 13.6-21.5 percent).
  • The risk of infection through contact outside the household was 5.1 percent (95% CrI 4.5-5.8 percent).
  • With increasing age, the risk of infection through household contact increased from 7.5 percent (95% CrI 1.3 to 20.3 percent) in children between the ages of 5 and 9 years to 30.2 percent (95% CrI 14.3 up to 48.2 percent) in children over 5 years of age 65 years of age.
  • The risk of infection through contact outside the household was greatest in the group of people of working age between 20 and 49 years.
  • Household contacts who were positive for antibodies but had no symptoms of COVID-19 had a 74.8 percent lower probability (95% CrI 43.8-90.3 percent) of infecting another household member than a positive contact who had symptoms (19.6 percent 95%). CrI 12.9-24.5 percent).

Conclusions and implications

This study shows that the risk of SARS CoV-2 infection after exposure to a single infected household member was four times higher than after positive external contact. The team found that younger children had a lower risk of infection from household contacts compared to older children, and that asymptomatic cases were less likely to transmit infection to contacts within the household. The authors wrote: "While the small households in Geneva limit the contribution of household diffusion, in other situations household diffusion is likely to play a bigger role."

* Important NOTE

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.

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