A new retrospective, laboratory-based observational study provides detailed insights into the causes of fevers of unknown origin in sub-Saharan Africa. Together with scientists from Guinea and Slovakia, researchers from the German Center for Infection Research (DZIF) at Charité—Universitätsmedizin Berlin examined 550 patients from Guinea who developed a persistent fever at the time of the major Ebola outbreak in 2014, but tested negative for the Ebola virus on site.