An Investigation of Chikungunya Outbreak in Kradangnga Subdistrict, Bang Khonthi District, Samut Songkhram Province, Thailand, September–November 2024

Abstract

On November 13, 2024, the Office of Disease Prevention and Control 5 Ratchaburi, received a report from the Samut Songkhram Provincial Public Health Office of 51 suspected chikungunya cases in Kradangnga Sub-district, Bang Khonthi District, Samut Songkhram Province. An outbreak investigation and control measures were conducted using descriptive epidemiology from September to November 2024 to confirm the diagnosis and verify the outbreak. The results showed that a total of 51 cases were identified, including 3 confirmed cases (5.88%) and 48 suspected cases (94.12%). The patients were male (31.37%) and female (68.63%), with the highest proportion in the 30–39 years age group. The primary occupation of the patients was farming (39.22%). Most patients initially sought care at private clinics or pharmacies (82.35%). The most common symptom was fever (100.0%), and no severe complications or deaths were reported. No genetic material of dengue virus, Zika virus, or chikungunya virus was detected in the laboratory investigations. Entomological surveillance revealed that larval indices were high in residential communities, temples, and schools. Control measures including larval source elimination and weekly monitoring operations were implemented. In addition, vehicle-mounted ultra-low volume (ULV) fogging and thermal fogging were conducted. After the operations, the larval indices decreased, and no further cases were identified. This investigation revealed that delayed and incomplete case reporting hindered timely outbreak control, leading to widespread transmission. Therefore, comprehensive, complete, and timely case reporting through the Digital Disease Surveillance (DDS) system should be promoted to cover both public and private healthcare settings. For disease prevention and control, the 3-3-1 control measure should be strictly enforced on days 1, 7, 14, 21, and 28 of case onset, aiming for a House Index (HI) of 5 and a Container Index (CI) of 0 in schools, temples, and villages. Supplemental chemical spraying every 7 days should be maintained if active transmission continues to effectively terminate the outbreak.