Co-circulation of Dengue and Chikungunya Viruses and Pre-Analytical Challenges During an Outbreak Investigation on Anjouan Island, Comoros, April 2025

Background In April 2025, suspected dengue cases were reported in Anjouan, Comoros, against a backdrop of chikungunya outbreaks in neighboring islands of the Indian Ocean. Objective To confirm the circulation of dengue (DENV) and chikungunya (CHIKV) viruses by triplex RT-PCR and to evaluate the quality of the sample handling process. Methods Seventy-three (73) blood samples from symptomatic patients were analyzed. RNA was extracted and tested by triplex RT-PCR (DENV/CHIKV/ZIKV). The internal control PPIA validated nucleic acid integrity. Results Only forty (40) samples (54.8%) were suitable for analysis. Among these, 30.0% were positive for DENV, with 33.3% of the positive samples showing co-infection with CHIKV. No Zika cases were detected. The high rate of non-conforming samples (45.2%) was linked to inadequate transport conditions (temperature, damaged tubes). Conclusion This study confirms the co-circulation of DENV and CHIKV in Anjouan. The high rate of invalid samples underscores the urgent need to strengthen the pre-analytical chain for effective arboviral surveillance in the Comoros archipelago.