Classical fever of unknown origin in 21 countries with different economic development: an international ID-IRI study - Hakan Erdem; Magdalena Baymakova; Sevil Alkan; Amel Letaief; Wissal Ben Yahia; Farouq Dayyab; Entela Kolovani; Svjetlana Grgic; Federica Cosentino; Imran Hasanoglu; Reham Khedr; Andrea Marino; et al. (European Journal of Clinical Microbiology & Infectious Diseases, 2023)