[Acute undifferentiated febrile illness among outpatients: differential diagnosis between dengue, zika, Argentine hemorrhagic fever and COVID-19].

The "acute undifferentiated febrile illness" (AUFI) encompasses a range of diseases characterized by the presence of fever, often prompting consultations in emergency services. During epidemics like COVID-19 or dengue, a surge in consultations occurs, resulting in long wait times for patients. Errors in first diagnosis can result in severe consequences. The objective is to provide a comprehensive review of the clinical approach to AUFI, focusing on certain viral infections (dengue, zika, Argentine hemorrhagic fever and COVID-19). This involves a detailed examination of the clinical presentation, laboratory and radiological findings, neurological manifestations, and definitive diagnosis through specific serological tests. AUFI is characterized by the onset of acute fever lasting less than seven days, accompanied by myalgia or headache without involvement of the upper respiratory tract and without a defined cause. Most cases are caused by common, self-limiting viral infections (e.g., influenza); however, they may also stem from more serious viral infections with a broad etiological spectrum. The differential diagnosis of acute febrile syndromes includes various infectious diseases, such as those previously mentioned. The definitive diagnosis is based on serological methods, PCR and IgM. Recommendations based on scientific evidence can help with early diagnosis and prevent possible serious complications.