COVID-19: Cluster of Covid-19 cases in the French Alps, 2020

COVID-19: Cluster of Covid-19 cases  in the French Alps, 2020. Spencer EA, Heneghan C.

Published on July 2, 2020

Reference Danis K, Epaulard O, Bénet T, et al. Cluster of coronavirus disease 2019 (Covid-19) in the French Alps, 2020 [published online ahead of print, 2020 Apr 11].  Clin Infect Dis. 2020;ciaa424. 2020
Study type
Country France, England and Spain
Setting French holiday chalet and subsequent home community settings
Funding Details All authors are employees of publicly funded institutes. There was no external funding for this work.
Transmission mode Person to person, close contact, superspreading
Exposures Holiday chalet

Bottom Line

This study highlights the variation possible in transmission between close contacts and also that cases’ clinical experience is highly variable including asymptomatic.

Evidence Summary

Subsequent to identifying the index case in a French holiday chalet, SARS-CoV-2 was detected in 11 additional people: 5 in France (including 1 child), 5 in England, 1 in Spain: overall attack rate in the chalet: 75%. 

One paediatric case, with picornavirus and influenza A coinfection, visited 3 different schools while symptomatic. No resulting transmission was identified. 

The paediatric case was coinfected with picornavirus (rhinovirus or enterovirus) + influenza A(H1N1)pdm09 co-infection. His two siblings were negative for the SARS-CoV-2, but positive for an Influenza A(H1N1)pdm09 infection, and an Influenza A(H1N1)pdm09 + picornavirus co-infection.

One case was asymptomatic, with similar viral load as that of a symptomatic case. 

Seven days after the first cases were diagnosed, one tertiary case was detected in a symptomatic patient with a positive endotracheal aspirate; all previous and concurrent nasopharyngeal specimens were negative. 

Among the 72 tested contacts, other seasonal respiratory viruses were detected in 46 (64%), representing 62% and 67% of high and low risk contacts

Additionally, 172 contacts were monitored, including 73 tested negative for SARS-CoV-2.

Source: Cluster of coronavirus disease 2019 (Covid-19) in the French Alps, 2020. Clin Infect Dis. 2020;ciaa424. doi:10.1093/cid/ciaa424

What did they do?

On 7th February 2020, French health authorities were informed of a confirmed case of SARS-CoV-2 coronavirus in an English man infected in Singapore who had recently stayed in a chalet in the French Alps. 

The index case stayed 4 days in the chalet with 10 English tourists and a family of 5 French residents. An investigation to identify secondary cases and interrupt transmission was conducted.

Low-risk contacts were asked to measure their body temperature twice a day during a 14-day period after their last exposure, and, in case of fever or respiratory symptoms to wear a surgical mask and contact the emergency hotline. High/moderate risk contacts were isolated at home, and were actively followed up through daily calls. 

Due to the large number of contacts of the sole paediatric case, particular attention was paid to detect tertiary cases in children in the three schools the child attended while symptomatic.

For case confirmation, nasopharyngeal swab or endotracheal aspirate samples were taken and tested via real-time reverse transcription PCR. A confirmed case was defined as a person linked to the chalet with a positive RTPCR sample for SARS-CoV-2.  

Study reliability

This study attempted detailed and relatively comprehensive contact tracing and monitoring. Given the relatively small sample, it is not possible to know how replicable these results are. 

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

What else should I consider?

This study gives detailed descriptions of contacts and apparent transmission, including interesting and relevant information on lack of transmission, and coinfections. 

It seemed as though one case infected 11 others – a “superspreading” event; all these were infected at the chalet together. 

The apparent dissociation between upper and lower respiratory tract results highlights the need for close monitoring of the clinical evolution of suspect Covid-19 cases.

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.