Settings linked to SARS-CoV-2 transmission clusters

Settings linked to SARS-CoV-2 transmission clusters.
Spencer EA, Heneghan C, Jefferson T.

Published on June 5, 2020

Reference Leclerc QJ, Fuller NM, Knight LE et al. What settings have been linked to SARS-CoV-2 transmission clusters? [version 1; peer review: 1 approved with reservations]. Wellcome Open Res 2020, 5:83 (
Study type
Country Worldwide (results mostly from Asia)
Setting A range of settings including the community and healthcare
Funding Details None specifically for the project; individual author funding statements reported.
Transmission mode Person to person, Close Contact
Exposures Clusters of cases defined as groups of first-generation cases that acquired the infection due to transmission in a single specific setting at a specific time

Bottom Line

The results found evidence of SARS-CoV-2 transmission clusters for 152 events, which was classified into 18 types of settings.

For the references see the online database.

Evidence Summary

Transmission from index cases was reported in a range of settings, including households, healthcare facilities, worker dormitories and indoor social spaces (two-thirds were associated with indoor settings. The setting with the greatest number of reports of transmission was households (29/152).

There are no data from mass gatherings such as sporting events or parades.

What did they do?

This systematic review described what is known about COVID-19 transmission in all settings worldwide, in order to inform public policy on removing current movement and contact restrictions. The authors searched three sources for data on transmission from index cases:

  • PubMed literature search up to 30 March 2020 for published research articles
  • Google search for media reports
  • Publicly available data sources searched for first 100 cases in each country experiencing an outbreak at the time

With the data, the authors estimated the final proportion of people in that setting who became infected and secondary proportion of contacts of one case who became infected in each setting.

A setting was defined when several reports mentioned clusters linked to certain spaces with specific characteristics. Where settings were a mixture of indoor and outdoor spaces they used a mixed indoor/outdoor classification.

Study reliability

The current evidence has several limitations that prevent firm conclusions to be drawn. Many of the reports came from media article, and many of the studies originated from the early outbreak in China which may not be generalisable. Systematic error due to differences in accuracy or completeness of recall to the memory of past events or experiences will likely have occurred in many of the studies (see Recall Bias). Multiple opportunities for transmission were not also accounted for. We can not conclude the likelihood of transmission at one type of setting versus another, as data for so many settings, including very large groups of people, are missing and there are issues with reporting bias.

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Yes Unclear Unclear Unclear Unclear

What else should I consider?

There is a lack of data on transmission at mass gatherings, such as sporting events or parades. Also, the study is as of 2 June 2020 under peer review and a revised version will include relevant updates. Dashboards such as the Singapore database provide in-depth information on the transmission that other geographical regions should consider replicating.

Back to the review

About the authors

Carl Heneghan

Carl is Professor of EBM & Director of CEBM at the University of Oxford. He is also a GP and tweets @carlheneghan. He has an active interest in discovering the truth behind health research findings

Elizabeth Spencer

Dr Elizabeth Spencer; MMedSci, PhD. Epidemiologist, Nuffield Department for Primary Care Health Sciences, University of Oxford.