Acknowledgements
We thank Martial Mettendorff, Deputy Director of Santé publique France for his support in the early phase of the investigations.

Investigation team
Santé publique France, Direction des régions, Cellule Régionale Nouvelle Aquitaine, Bordeaux, France: Laurent Filleul, Stéphanie Vandentorren.
Santé publique France, Direction des régions, Cellule Régionale Auvergne-Rhône-Alpes, Lyon, France: Guillaume Spaccaferri.
Santé publique France, Direction des régions, Cellule Régionale Hauts-de-France, Lille, France: Hélène Prouvost.
Centre national de référence Virus des infections respiratoires, dont la grippe, Institut Pasteur, Paris, France: Mélanie Albert, Marion Barbet, Angela Brisebarre, Flora Donati, Sylvie van der Werf.
Agence Régionale de Santé Ile-de-France, Paris, France: Alexis Ardoin, Marion Dreyer, Karim Tararbit.
Agence Régionale de Santé Nouvelle-Aquitaine, Bordeaux, France: Matthieu Amodeo, Elodie Couaillier, Pascal Fabre, Daniel Habold.
Santé publique France, Direction des maladies infectieuses, Saint-Maurice, France: Didier Che.
AP-HP, Hôpital Bichat, Service des maladies infectieuses et tropicales, Paris, France: Gisèle Bendjelloul, Marine Billaudelle Lallemant, Valentine Charachon, Laurène Deconinck, Diane Descamps, Sandrine Gérard, Nadirha Houhou, Quentin Le Hingrat, Isabelle Lolom, Jean-Christophe Lucet, Annabelle Pourbaix, Simon Valayer, Yazdan Yazdanpanah.
Centre Hospitalier Universitaire de Bordeaux, Bordeaux GeoSentinel Site, Bordeaux, France: Alexandre Boyer, Benjamin Clouzeau, Xavier Combes, Arnaud Desclaux, Jean-Michel Dindart, Alexandre Duvignaud, Isabelle Garrigue, Didier Gruson, Marie-Edith Lafon, Pauline Perreau, Thierry Pistone, Maxime Poteau, Eric Tentillier.
Direction Générale de la Santé, Ministère des solidarités et de la santé, Centre opérationnel de réception et de régulation des urgences sanitaires et sociales, Paris, France: Pauline Mathieu

Conflict of interest: None declared.
Authors’ contributions: All authors provided critical feedback on the manuscript.
Sibylle Bernard Stoecklin, Bruno Coignard and Daniel Levy-Bruhl wrote the manuscript with input from all authors.
Sibylle Bernard Stoecklin, Patrick Rolland, Alexandra Mailles, Christine Campese, Didier Che, Clément Lazarus, Anouk Tabaï, Morgane Stempfelet, Bruno Coignard and Daniel Levy-Bruhl contributed to the design and implementation of the surveillance system, as well as the coordination between all parties involved in the surveillance.
Patrick Rolland, Yassoungo Silue, Alexandra Mailles, Christine Campese, Anne Simondon, Matthieu Mechain, Laure Meurice, Mathieu Nguyen, Clément Bassi, Estelle Yamani, Scarlett Georges, as well as all members of the investigation team contributed to the investigations and the active surveillance of contacts.
Sophie Ismael, Duc Nguyen, Denis Malvy and François Xavier Lescure are the clinicians in charge of the three 2019-nCoV cases and contributed to data collection on clinical history, exposure and contacts.
Sylvie Behillil and Vincent Enouf contributed to the laboratory confirmation of 2019-nCoV infection in the three imported cases, as well as the testing of samples of possible cases.

Supplementary Data
Supplement
Click here for additional data file.