An ECSA-lineage chikungunya outbreak in Foshan, China: age-stratified clinical and virological profiles

Since July 2025, Foshan has experienced the largest outbreak of Chikungunya fever in China. This single-centre retrospective study included 1,908 laboratory-confirmed cases. Phylogenetic analysis identified the East/Central/South African lineage, closely related to the 2025 La Réunion strain. The included cases were all non-severe, showed no sex bias, but exhibited clear regional clustering. Fever (86.8%), arthralgia (85.4%), and rash (64.1%) were predominant symptoms. Fever and rash were more common in minors, while arthralgia increased with age. Lymphopenia occurred in 65.5% of patients and was more common in elderly patients, who had higher viral loads and longer RNA clearance times. Age, sex and viral load independently influenced clinical manifestations and laboratory characteristics. The findings provide initial descriptive evidence and highlight age-related differences in chikungunya's clinical and virological profiles. Long-term follow-up and larger-scale investigations were necessary to provide evidence for clinical decision-making.