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.

At least three cases of dengue fever have been reported in residents bitten by local mosquitoes in the Baldwin Park neighborhood east of downtown Los Angeles.

“Dengue is primarily transmitted through the bite of an infected Aedes mosquito. Although Aedes mosquitoes are common in LA County, cases of locally acquired dengue are extremely rare,” Los Angeles County Public Health Director Barbara Ferrer said Wednesday.

For the first time in California, health officials have reported a cluster of dengue fever cases that are not travel-related and warned residents to protect themselves from mosquito bites. Two more locally acquired cases of the mosquito-borne illness dengue have been detected in Baldwin Park residents,

There has been a rare uptick of the dengue virus in the US this year, with people being urged to look out for the symptoms. Los Angeles County has reported three locally acquired cases of dengue this year,

Health officials reported a single case of locally acquired dengue in Long Beach last year. Now, three such cases in Baldwin Park mark an unprecedented escalation.