The Pasadena Public Health Department has reported a case of Dengue virus in a Pasadena resident, the first confirmed incident of the mosquito-borne disease in the entire state not associated with travel outside the United States.
Dengue viruses are spread from an infected Aedes species mosquito to people they bite, which could cause symptoms of fever, nausea, vomiting, rash, and aches and pains to the eyes, muscles, joints or bones, according to the Centers for Disease and Control.
Although about half the world’s population lives in areas with a risk of dengue, local transmission within the U.S. is rare and the risk of exposure remains low, officials emphasized Friday, Oct. 21, at Pasadena City Hall.
In 2023 to date, there have been more than 500 reported cases of locally acquired dengue in the U.S. — until Friday all occurring in Texas, Florida and Puerto Rico.
“Pasadena Public Health Department has been conducting surveillance and investigation of mosquito-borne diseases in Pasadena for years,” Dr. Matthew Feaster, PPHD Epidemiologist said.
“Our work so far, in partnership with the Vector Control District, gives us confidence that this was likely an isolated incident and that there is very low risk of additional dengue exposure in Pasadena.”
The resident who contracted the virus is recovering, Feaster noted, declining to disclose details for privacy reasons.
Just how the virus was contracted locally was a matter still be probed.
“We are continuing our investigation,” Feaster said. “It may take a lot of time to understand how that might have occurred.”
What officials do believe, Feaster said, is that the transmission that occurred had to have happened after someone went to a foreign country, got infected with dengue virus in an area where dengue was common, flew home, and then had enough virus circulating that when they were bit by a mosquito, it then transmitted to a local resident in Pasadena.
According to Feaster, the unidentified patient initially reported symptoms in mid September and the department was made aware of the results by the first week of October.
Record rainfall earlier in the year combined with humid conditions recently -– punctuated by Hurricane Hilary in August -– has driven a surge in the mosquito population, said Jason Farned,district manager for the San Gabriel Valley Mosquito and Vector Control District, which estimates mosquito populations locally are four times their average, increasing the risk for disease.
In response, the San Gabriel Valley Mosquito and Vector Control District has deployed traps to assess the mosquito population and earlier this month implemented residential mosquito control applications in Pasadena.
Farned said that to date across the testing area, no mosquitos have tested positive for carrying dengue.
“Pasadena is working with healthcare providers to raise awareness of the signs and symptoms of dengue infection and is coordinating prevention efforts with local and state public health officials,” stated Interim Health Officer, Dr. Parveen Kaur. “Eliminating mosquito breeding sources is essential to reducing the spread of mosquitoes and the diseases they carry.”
PPHD recommends the following practices to reduce mosquito populations and prevent the spread of disease:
- Eliminate standing water in clogged rain gutters, rain barrels, discarded tires, buckets, watering troughs, or anything that holds water for more than a week.
- Ensure that swimming pools, spas, and ponds are properly maintained.
- Change the water in pet dishes, birdbaths, and other small containers weekly.
- Report neglected swimming pools in your neighborhood to your vector control district.
- Wear insect repellent containing CDC and EPA approved active ingredients: DEET®, picaridin, IR3535, or oil of lemon eucalyptus.
- Wear loosely fitted, light-colored, long-sleeved shirts and long pants.
Farned said Vector Control will continue to test at least through the next few weeks.
City Editor Ryan Carter contributed to this article.
This story has been corrected to note that no mosquitos have tested positive for Dengue.