Aneruptive Fever Associated with Antibodies to Rickettsia helvetica in Europe and Thailand

We report that eight patients from France, Italy, and Thailand had serological evidence of Rickettsia helvetica infection. The infection presented as a mild disease in the warm season and was associated with fever, headache, and myalgia but not with a cutaneous rash. R. helvetica should be suspected in patients with unexplained fever, especially following a bite from an Ixodes sp. tick.