Influenza in travelers from Germany returning from abroad: a retrospective case-control study

Influenza is the most common vaccine-preventable infection among travelers, affecting approximately one percent of those travelling to subtropical and tropical destinations. We analysed demographic, travel-related and clinical information from travelers diagnosed with influenza at our travel clinic between January 2015 and March 2020 and influenza-negative controls. We included 68 travelers diagnosed with influenza and 207 controls. In total, 22.1% of influenza patients (n = 15) were older than 60 years and/or had comorbidities for which annual influenza vaccination is recommended, but only one had received an influenza vaccine. Patients with respiratory and musculoskeletal symptoms who presented during the German influenza season had the highest risk proportion of positive tests (54%, n = 25/46). Overall, three (4.4%) influenza patients were hospitalised, two (2.9%) received antiviral treatment, and eight (11.8%) received antibiotic therapy. Influenza occurs throughout the year in international travelers and can cause significant morbidity. Travelers with febrile illness should be tested for influenza, especially if they have respiratory or musculoskeletal symptoms, present during the local influenza season, or have travelled to South-East Asia. Influenza vaccination coverage among international travelers needs to be improved among high-risk individuals.