Valley Fever cases are climbing in California, particularly in the Central Valley.
The number of people who got sick in 2016 was the highest it's been since 1995, the state health department announced Thursday.
Ther were 5,372 new cases last year, compared to just 3,140 cases in 2015, according to the California Department of Public Health. The incidence rate in Stanislaus County jumped by 42 percent.
The agency does not know the cause of the increase.
"The incidence of Valley Fever depends on a variety of environmental factors and types of human activity in areas where the fungus is present," health officials said in a statement.
Valley Fever is caused by a soil-dwelling fungus called Coccidioides, which pervades in agricultural areas such as the San Joaquin Valley. The fungus spores travel in dust, so risk is high for workers doing construction or other outdoor jobs.
Once in the lungs, the spores can cause cough, chills and chest pain.
The health department warns Central Valley residents to stay inside on windy days and keep car windows closed while driving. When working outdoors, officials recommend wearing a properly fitted mask.