Cases of Valley fever in Arizona spiked last month and researchers say that could indicate an increase next year.

About 900 cases of Valley fever were reported in November — nearly a 50 percent increase from the month before. Caused by a fungus found in the desert soil, the disease often affects the respiratory system. The majority of people infected don’t experience symptoms, but less than five percent can have much more serious complications.

Dr. John Gagliani, director of the University of Arizona’s Valley Fever Center for Excellence, said that lots of precipitation at the end of last year could be driving the uptick now.

“With a heavy rain in the offseason, there’s a bloom of the fungus in the soil and the consequences would be that later when things dry out there are more spores that get in the air and that raises the risk of inhaling them,” he said.

He said past data suggested that the rise in cases could continue into next year.