Close contact and risk of SARs-CoV-2 infection

Close contact and risk of  SARs-CoV-2  infection. Spencer EA, Jefferson T, Heneghan C.

https://www.cebm.net/study/covid-19-close-contact-and-risk-of-sars-cov-2-infection/

Published on June 22, 2020

Reference Liu Y, Eggo RM, Kucharski AJ. Secondary attack rate and superspreading events for SARS-CoV-2. Lancet. 2020;395(10227):e47
Study type
Country China and France
Setting Specific events associated with transmission such as a family gathering.
Funding Details Non reported
Transmission mode Close contact, person to person
Exposures Household contacts, gatherings, shared accomadation

Bottom Line

In transmission events, after sharing a meal or staying at a chalet the secondary attack rate is estimated as very high.

Evidence Summary

In transmission events, after sharing a meal or staying at a chalet the secondary attack rate is estimated as very high at around 35%. There is variation between these nine events. 

Setting   The number at the gathering (excluding indeed case) Number infected 
Meal (homeΩ0 8 8  (100%)
Meal (home) 13 4 (31%)
Meal (unknown) 1 1 (100%)
Meal (unknown) 14 3(21%)
Meal (restaurant) 14 3 (21%)
Meal (unknown) 17 2 (12%)
Meal (unknown) 47 10(21%)
Chalet 11 5
Meal  18 8

What did they do?

This is a journal letter and the full details of the methods can not be obtained. The authors estimated the secondary attack rate from a number of cases in Wuhan, up until 27th February 2020. 

Study reliability

This is an early estimate of transmission from one location early in the pandemic so is unlikely to reflect a wider context and is unlikely to be reproducible. This is a small study.  The time duration of exposure is not investigated here but is likely to impact transmission in different contexts.  The authors note that reports at that time may have been biased towards larger transmission events. There is also an assumption that all the secondary infections were generated by a single primary case.

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Unclear No Unclear Yes No

What else should I consider?

The authors point out that “if it transpires that most at-risk contacts have a close relationship with cases, and superspreading events tend to occur at large gatherings of these close contacts, measures to reduce infection risk during such gatherings and subsequent tracing of close contacts of cases might have a disproportionate effect on reducing overall transmission.”

About the authors

Carl Heneghan

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

Elizabeth Spencer

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

Tom Jefferson

Tom Jefferson

Tom Jefferson is a senior associate tutor and honorary research fellow, Centre for Evidence-Based Medicine, University of Oxford.