RENBP and Fever: All archived samples containing sufficient quantities of serum (~ 20 - 25 μL) with a diagnosis of "antigen positive" (Ag+) determined by a traditional Ag-capture assay (Trad Ag) developed by the United States Army Medical Research Institute of Infectious Diseases (USAMRIID), a recombinant Ag-capture assay for LASV NP developed by the Hemorrhagic Fever Virus Diagnostics Consortium, or from patients presenting with classical clinical symptoms of Lassa fever were used in this study.