Investigation of and Response to Autochthonous Dengue, Los Angeles County, California, USA, August-November 2024

Dengue is not endemic in the continental United States; most cases occur in returning travelers. During August-November 2024, a total of 14 locally acquired cases of dengue were identified in Los Angeles County, California, USA. Epidemiologic evidence indicates that locally acquired cases occurred in several neighborhoods, suggesting short transmission chains after introductions from returning travelers. In one neighborhood, evidence supported ongoing transmission for up to 7 weeks. Median patient age was 54 (range 5-79) years; 8 (57%) patients were female and 6 (43%) male, and 6 (43%) required hospitalization. Delays in healthcare seeking and diagnoses were noted; median time from symptom onset to specimen collection for dengue testing was 9 (range 2-34) days. Local dengue transmission in Los Angeles County highlights the emerging threat of mosquitoborne disease transmission in nonendemic areas and the need for rapid and coordinated public health and vector control responses to interrupt transmission.