A team of scientists in the United States recently estimated the risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission from primary cases to household contacts.
By stratifying the transmission risk by age, they have observed that both children and adults are equally susceptible to acquire SARS-CoV-2 infection and can transmit the virus to their family members. The study is currently available on the medRxiv* preprint server.
This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources
Background
Clinical severity of coronavirus disease 2019 (COVID-19), a novel disease caused by SARS-CoV-2, is highest among older adults above the age of 65 years. In contrast, children with SARS-CoV-2 infection mostly remain asymptomatic or mildly symptomatic. Similarly, most available information suggests that children are less likely to acquire SARS-CoV-2 infection as well as transmit the virus to others, with only a few studies indicating that there are no age-related differences in susceptibility and transmission risk.
Such discrepancies between studies could be due to variations in the frequency of interaction, contact tracing, or testing practices. To better manage the COVID-19 pandemic, it is important to understand the age-related differences in susceptibility, transmission risk, and clinical consequences.
In the current study, the scientists have examined the risk of household SARS-CoV-2 transmission from primary cases, as well as the risk of infection acquisition among household contacts stratified by age. Moreover, they have investigated the age-related differences in disease severity and duration among secondary cases.
Study design
The study was conducted on 226 individuals with laboratory-confirmed SARS-CoV-2 infection (primary cases) and their household contacts. All participants were monitored daily for 14 days to examine the incidence of secondary infections and associated symptoms.
The participants were divided into 6 groups according to their age: preschool (0 – 4 years), primary school (5 – 11 years), secondary school (12 – 17 years), young adults (18 – 49 years), middle-aged adults (50 – 64 years), and older adults (≥65 years).
The risk of viral transmission to household contacts was estimated according to the age of the primary case; whereas, the risk of infection among household contacts was estimated according to the age of contacts. Moreover, the severity and duration of symptoms were assessed for all participants.
Important observations
A total of 226 primary cases with 404 household members were examined in the study. The majority of individuals with primary infection were non-Hispanic White young adults. About 80% of participants reported having pre-existing medical conditions, with 36% having asthma.
Regarding household size, about 83% of primary cases mentioned living in a single-family home with an average of 3 family members. A reduction in the frequency of interactions between primary cases and household contacts was observed between the day before disease onset and the day before study enrollment.
Risk of viral transmission and infection
Of 404 household contacts, 197 acquired SARS-CoV-2 infection from 226 primary cases. The risk of secondary infection from primary cases aged 12 – 17 years was significantly lower than that from primary cases aged 18 – 49 years. The risk of secondary infection was lowest from primary cases aged 12 – 17 years (25%) and highest from primary cases aged ≥65 years (76%). However, no significant difference in the secondary infection risk was observed when estimated by the age of household contacts.
Interestingly, a comparatively higher risk of secondary infection was observed when the primary cases and contacts belonged to the same age group. When the risk of secondary infection was estimated by pairing the age groups of primary cases and household contacts, the highest risk was observed among participants aged 5 – 11 years and ≥65 years.
Symptoms associated with secondary infection
Of 186 household contacts with secondary SARS-CoV-2 infection, about 81% reported having at least one symptom, and 19% reported no symptom. Of 150 symptomatic contacts, 46% tested positive for SARS-CoV-2 before the symptom onset. The average duration between the first positive test result and symptom onset was 2 days.
Among children and adolescents, upper respiratory tract symptoms were the most common. In contrast, lower respiratory tract symptoms were commonly observed in adults aged ≥50 years. Although less common than other symptoms, gastrointestinal symptoms were observed in 50% of children aged 5 – 11 years and 60% of adults aged 18 – 49 years.
No significant difference in average symptom duration (8 days) was observed between different age groups. However, for constitutional symptoms (symptoms that are not directly disease-specific), the duration increased significantly with age, ranging from 2 days in young children (<12 years) to 9 days in older adults (≥65 years). For neurological symptoms, the duration was significantly higher in adults aged 50 – 64 years (10 days) compared to that in other age groups (4 days).
Study significance
The study findings reveal that both children and adults are equally susceptible to SARS-CoV-2 infection and equally potential to transmit the infection to other family members. Infected older adults aged ≥65 years have the highest potential to transmit the virus to other family members. In contrast, infected adolescents aged 12 – 17 years have the lowest potential to transmit infection.
This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources
Article Revisions
- Apr 12 2023 - The preprint preliminary research paper that this article was based upon was accepted for publication in a peer-reviewed Scientific Journal. This article was edited accordingly to include a link to the final peer-reviewed paper, now shown in the sources section.
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