SACRAMENTO (CBS SF) — The state health department says there was a record number of Valley Fever cases reported in 2016.

Valley Fever is caused by fungus spores that travel in dusty air. When inhaled, they can cause flu-like symptoms. Cases are most common in south Central Valley farmlands and fields around Fresno and Kern counties.

In 2016, more than 5,300 cases were reported.

No one knows why there was a spike in cases last year.

The elderly, African-Americans, Filipinos, pregnant woman, people with diabetes or compromised immune systems are most susceptible.