On Oct. 6, 2024, San Diego County officials announced they were investigating the first ever case of locally acquired dengue. The Escondido resident who became sick with dengue did not travel to an area where the mosquito transmitted illness was common. No additional locally acquired cases had been identified to date. 

Los Angeles County had reported five cases of locally contracted dengue in the year. Long Beach and Pasadena had their first cases of locally acquired dengue in late 2023.  Dengue is spread by mosquitoes, when a mosquito bites an infected person and then feeds on another person.  It can take four to seven days for someone who is bitten by a mosquito infected with dengue to start feeling symptoms. Dengue can be determined by a blood test.