The fungus is sensitive to environmental changes, experts say, and a hotter, drier climate has increased dust carrying the spores.
‚ÄúResearch has shown that when soil is dry and it is windy, more spores are likely to become airborne in endemic areas,‚ÄĚ said Dr. Gil Chavez, Deputy Director of the Center for Infectious Diseases at the California Department of Public Health.
Longstanding concerns about valley fever were heightened last week when a federal health official ordered the transfer of more than 3,000 exceptionally vulnerable inmates from two San Joaquin Valley prisons where several dozen have died of the disease in recent years. A day later, state officials began investigating an outbreak in February that sickened 28 workers at two solar power plants under construction in San Luis Obispo County.
Although millions of residents in Central California face the threat of valley fever, experts say people who work in dusty fields or construction sites are most at risk, as are certain ethnic groups and those with weak immune systems. Newcomers and visitors passing through the region may also be more susceptible.
Nationwide, the number of valley fever cases rose by more than 850 percent from 1998 through 2011, according to the Centers for Disease Control and Prevention. In 2011, there were nearly 22,000 cases, with most cases reported in California and Arizona.
In California, according to the CDC, valley fever cases rose from about 700 in 1998 to more than 5,500 cases reported in 2011. The disease has seen the sharpest rise in Kern County, followed by Kings and Fresno counties.
Out of the 18,776 California cases between 2001 and 2008, 265 people died, according to the state health department.
Arizona saw an even steeper rise: The number of reported cases there went from 1,400 in 1998 to 16,400 in 2011, with the highest rates of infection occurring in Maricopa, Pima and Pinal counties.
Drought periods can have an especially potent impact on valley fever if they follow periods of rain, said Prof. John Galgiani, director of the Valley Fever Center for Excellence at the University of Arizona. Rainfall leads to fungus bloom, but limits dust.
‚ÄúWhen it dries up, that‚Äôs when the fungus goes into the air,‚ÄĚ Galgiani said. ‚ÄúSo when there is rain a year or two earlier, that creates more cases if drought follows.‚ÄĚ
Another reason for the increase in cases, Galgiani said, is new residents, who are more susceptible to the disease, relocating to areas with the spores.
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