Imported fever in returning travellers and migrants in Spain, 2009-2021. Analysis by the +REDIVI network.

Background: Travellers and migrants commonly present to health services with febrile syndrome, which can have different causes, including some that are life-threatening. A better understanding of these causes may help guide management and determine appropriate empirical treatments.

Objective: The aim was to identify the leading causes of fever and to assess their association with the region of travel and type of travellers.

Methods: This prospective, multicentre study was conducted within the +REDIVI network. Data were collected on febrile syndrome cases among migrants, travellers, and people visiting friends and relatives (VFRs) from 2009 to 2021. Comparative analyses were performed according to patient categories and regions of travel/origin.

Results: Of the 4186 patients with febrile syndrome, the most frequent diagnosis was malaria (31.0 %), followed by dengue fever (12.0 %) and nonspecific fever of less than three weeks' duration (11.6 %). Malaria predominated in people coming from sub-Saharan Africa (58.4 %), while dengue fever was more common in the rest of the regions (19.0 % in South America, 25.0 % in Central America and the Caribbean, 34.2 % in Southeast Asia, and 18.1 % in South-Central Asia). By type of traveller, tuberculosis was more frequent in migrants, malaria in VFRs, and dengue and other arboviral infections in travellers and VFRs.

Conclusions: Geographical area of travel and type of traveller are the main determinants of imported fever aetiology. Malaria remains the most common cause of febrile syndrome, especially in VFRs from sub-Saharan Africa, while dengue fever prevails in the other tropical regions.