Travellers as sentinels of chikungunya epidemics: a family cluster among Finnish travellers to Koh Lanta, Thailand, January 2019.

In January 2019, five of 11 travellers to Koh Lanta, Thailand, contracted chikungunya, symptoms starting 4 days after presumed transmission. Four cases were hospitalised, one child treated in intensive care; 6 weeks after disease onset, all three adults have persistent arthralgias/arthritis, incapacitating for two. Together with a recent report of eight chikungunya cases among travellers to various destinations in Thailand, the high attack rate in our cluster points to an ongoing outbreak in the country.