Symptom overlap in chikungunya and dengue: A diagnostic challenge during outbreaks.

Distinguishing dengue from chikungunya at presentation is difficult in co-circulation settings due to substantial symptom overlap. In November 2023, São José do Rio Preto, São Paulo, Brazil, a dengue-endemic city, faced its first recognized chikungunya outbreak, challenging frontline triage and surveillance. We conducted a hospital-based retrospective cross-sectional study (November 2023-August 2024), integrating clinical variables with RT-qPCR confirmation to compare syndromic profiles and severity markers between dengue and chikungunya. Neurological cases were captured through active surveillance and are reported as an additional descriptive analysis (CDC neuroinvasive disease criteria), because they did not meet the serum RT-qPCR inclusion criterion for the comparative analysis. Among 1819 patients analyzed, 223 were dengue-positive and 144 chikungunya-positive. Fourteen manifestations overlapped. Compared with chikungunya, dengue more frequently presented fever, headache, vomiting, ocular pain, thrombocytopenia, and leukopenia, whereas chikungunya more often presented rash and joint pain. Warning signs were more frequent in dengue. Despite some discriminating features, clinical overlap predominated and limited diagnostic accuracy; virological confirmation by specific tests remains essential where arboviruses co-circulate.