This dataset presents the results from a prospective diagnostic study in which the diagnostic performance of the Sysmex Infection Manager System (IMS), which is a novel algorith equipped on a Sysmex hematology analyzer, was tested on a cohort of Indonesian adult patients presenting to a health facility with an acute febrile illness. All patients were evaluated using a structured diagnostic protocol. The total cohort was 600 patients of whom 137 were excluded. The IMS was first trained on the first 200 patients and subsequently validated on the complete cohort consisting of 463 patients. The etiology of the febrile illness was determined using a combination of clinical investigations, as well as a set of laboratory and radiology examinations. The performance of the IMS was compared to that of the biomarkers C-reactive protein (CRP) and procalcitonin (PCT)