Household contact may be the greatest risk for transmission of COVID-19

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Peer-reviewed: This work was reviewed and scrutinised by relevant independent experts.

Observational study: A study in which the subject is observed to see if there is a relationship between two or more things (eg: the consumption of diet drinks and obesity). Observational studies cannot prove that one thing causes another, only that they are linked.

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Researchers in China say household contact may be the main way COVID-19 is spread and that rates of secondary spread of the virus were far higher in homes than in healthcare settings or on public transport. The authors found that risk for secondary transmission of COVID-19 overall was less than 4 percent among close contacts of persons with COVID-19, while the risks for those in the same household were higher, with around a 10 per cent rate of secondary spread. They also found that the more severe the initial case was, the higher the risk for transmission among close contacts.

Journal/conference: Annals of Internal Medicine

Link to research (DOI): 10.7326/M20-2671

Organisation/s: Southern Medical University, China

Funder: By the Guangdong Province Higher Vocational Colleges and Schools Pearl River Scholar Funded Scheme, the National Natural Science Foundation of China, the Construction of High-level University of Guangdong, and the Zhejiang University Special Scientific Research Fund for COVID-19 Prevention and Control.

Media release

From: American College of Physicians

Household contact the greatest risk for transmission of COVID-19
Asymptomatic patients less likely to infect close contacts compared to severe cases
Secondary transmission acquired from public transportation was rare

Researchers from Southern Medical University, Guangzhou, China traced more than 3,410 close contacts of 391 COVID-19 index cases between January and March 2020 to evaluate the risk for disease transmission in different settings. They found that risk for secondary transmission of COVID-19 was less than 4 percent among close contacts of persons with COVID-19. In addition, secondary infections acquired while using public transportation were rare. In contrast, 1 in 10 household contacts was found to be infected.

The researchers also found that patients with more clinically severe disease were more likely to infect their close contacts than were less severe index cases. Those with asymptomatic cases were the least likely to infect their close contacts. Manifestation of certain symptoms, such as expectoration, in index cases was also associated with an increased risk for infection in their close contacts.

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