A person in Maricopa County, Arizona, has been diagnosed with dengue fever, health officials announced this week, adding that this case could be the county’s first that was acquired locally, rather than from travel. If true, it would make Arizona just the second state so far this year to have a case that stemmed from a locally acquired infection.

There have been 10 other cases of dengue fever reported in Arizona from Jan. 1 through Nov. 2 of this year, according to the Centers for Disease Control and Prevention, but all those were travel-related. 

In a news release Monday, the Maricopa County Department of Public Health said the infected individual “might have been exposed by an infected mosquito” in the county. The virus was detected in one neighborhood amid routine surveillance by the county’s Environmental Services Department. 

“While previous dengue cases in Maricopa County have been related to travel to countries where dengue commonly occurs, it is important to understand if others could have been exposed or if this is an isolated incident,” medical epidemiologist Dr. Nick Staab said in a statement. “This is in addition to our routine investigations of anyone suspected to have dengue or other mosquito-borne diseases.”  

Dengue fever is spread through mosquito bites, although a fetus can also be infected if the carrying parent contracts the virus during pregnancy. While up to 400 million people get infected every year, with about 40,000 dying from severe illness, outbreaks in the U.S. only occasionally happen, the CDC says. Nearly all cases in the continental U.S. stem from travel.     

About 25% of infected individuals develop mild flu-like symptoms, Maricopa County health officials said, but about 1 in 20 people “can get severely ill.” 

So far this year, at least 888 cases of dengue fever have been reported in 36 states, according to the CDC. All but one state – Florida – had their cases exclusively stem from travel. Two territories – Guam and Puerto Rico – have also been hit with dengue cases, with the overwhelming majority of Puerto Rico’s cases being local-born. 

Maricopa County field teams made up of staff and volunteers are now offering dengue testing to residents ages 5 and older in the neighborhood where the latest case was discovered. The testing can identify an infection which might have occurred in the “last several months,” the county said. They are also providing residents with mosquito prevention kits.

The news comes months after a study published in the Frontiers in Public Health journal found that climate change has become “one of the key reasons” dengue fever transmission has become more intense. 

“The most important climatic factors linked to dengue transmission are temperature, rainfall, and relative humidity,” the study determined. 

Study authors did note that there still needs to be significant research in this area, and that “relationships between numerous environmental conditions and dengue transmission are complex and sometimes non-linear.” 

Rainfall and temperature are both important factors in the ability for mosquitos to lay eggs and develop, and the increasing extreme levels of both with climate change could contribute to changes in the spread of dengue fever, researchers said.