LOS ANGELES (AP) — Health officials warned Wednesday that the Los Angeles area is seeing more dengue fever cases in people who have not traveled outside the U.S. mainland, a year after the first such case was reported in California.

Public health officials said at least three people apparently became ill with dengue this month after being bitten by mosquitoes in the Baldwin Park neighborhood east of downtown Los Angeles.

“This is an unprecedented cluster of locally acquired dengue for a region where dengue has not previously been transmitted by mosquitoes,” said Barbara Ferrer, director of the Los Angeles County Department of Public Health.

Other cases that stemmed from mosquito bites originating in the U.S. have been reported this year in Florida, the U.S. Virgin Islands and Puerto Rico, where officials have declared a dengue epidemic. There have been 3,085 such cases in the U.S. this year, of which 96% were in Puerto Rico, according to the U.S. Centers for Disease Control and Prevention.

Cases of dengue have been surging globally as climate change brings warmer weather that enables mosquitoes to expand their reach.

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Dengue fever is commonly spread through the bite of infected Aedes mosquitoes in tropical areas. While Aedes mosquitoes are common in Los Angeles County, local infections weren’t confirmed until last year, when cases were reported in Pasadena and Long Beach.

Before then, the cases in California were all associated with people traveling to a region where dengue is commonly spread, such as Latin America, said Aiman Halai, director of the department’s Vector-Borne Disease Unit.

So far this year, 82 such cases have been reported in L.A. County by people returning from traveling, Halai said. Across California, there have been 148 cases.

Dengue can cause high fevers, rashes, headaches, nausea, vomiting, muscle pain, and bone and joint pain. About one in four people infected will get symptoms, which usually appear within five to seven days of a bite from a dengue-carrying mosquito. One in 20 people with symptoms will develop severe dengue, which can lead to severe bleeding and can be life-threatening.

Public health officials will be conducting outreach to homes within 150 meters (492 feet) of the homes of people who have been bitten. That’s the typical flight range of the mosquitoes that transmit the virus, according to Ferrer.

Ferrer recommended that people use insect repellent and eliminate standing water around their houses where mosquitoes can breed.

Officials have been testing mosquitoes for the disease and so far have not found any in the San Gabriel Valley with dengue.