On October 20, 2023, a locally acquired case of dengue was reported in Pasadena. While this is the first case of human local transmission in California, dengue is rare in the U.S. Public health officials believe this is an isolated incident and there is a very low risk of additional dengue exposure in the area. The San Gabriel Valley Mosquito & Vector Control District has deployed traps to assess the local mosquito population and, importantly, testing to date has not identified any dengue infected mosquitoes. 

Dengue is transmitted by Aedes aegypti (yellow fever mosquito) and Aedes albopictus (Asian tiger mosquito). These mosquitoes are not native to California, but they have been identified in 28 counties in California. Aedes aegypti has been identified in Butte County for four consecutive years. Dengue is transmitted to humans through the bite of an infected Aedes mosquito. Dengue cannot spread directly from human to human.

Dengue is common in many tropical and subtropical areas of the world where Aedes mosquitoes thrive like parts of Africa, the Middle East, India, Southeast Asia, South America, Central America, and North America (specifically Mexico). According to the California Department of Public Health, in 2022 there were 128 people in California with travel-associated dengue virus infections. 

While local transmission of dengue in the U.S. is rare, in December 2022 in Maricopa County, Arizona, two individuals tested positive for dengue they acquired from a mosquito bite locally. No additional cases were detected in the same area this year.

The best way to prevent dengue is to prevent mosquito bites, especially when traveling in tropical places. Residents are encouraged to wear EPA-registered insect repellent. It is also important to dump and drain all standing water in and around homes as invasive Aedes mosquitoes can develop in very small amounts of water. 

• To learn more about mosquito prevention please visit: https://buttemosquito.com/mosquito-prevention.
• To learn more about the locally acquired case, please visit the San Gabriel Valley Mosquito & Vector Control District and Pasadena Public Health Department.
• For general information about dengue, please visit the CDC and the California Department of Public Health.
• For an interactive map of where the District has discovered this mosquito click here.