California's tally of valley fever cases dropped by more than 1,000 last year and some counties have also seen fewer cases in the early months of 2013.
But public health officials say it's too early to identify long-term trends in the numbers.
"The number of reported cases in 2012 was still high compared to historical levels," Dr. James Watt, chief of the California Department of Public Health's Division of Communicable Disease Control, wrote in an email. "The public and health care providers in high incidence areas should be aware that valley fever remains an important public health concern."
Watt said the 20 percent overall decline between 2011 and 2012 is "good news" but "it is too soon to know whether this decrease will continue."
Valley fever, a disease caused by fungal spores that grow in soil, can have wide-ranging effects on the people it strikes. Many never know they have been exposed to the disease, while others suffer flu-like symptoms.
In serious cases, the disease spreads beyond a person's lungs, sometimes requiring lifelong treatment to keep it in check. The disease can be deadly. Valley fever was listed as an underlying or contributing cause of death in 3,089 deaths nationwide between 1990 and 2008, according to a study published last year.
Reported cases of valley fever, also known as coccidioidomycosis, in California dropped from 5,123 in 2011 to 4,094 in 2012, according to new California Department of Public Health data. The 2012 total is still more than twice as many cases as the 1,727 reported in California in 2002, according to the Centers for Disease Control and Prevention.
Arizona saw a similar drop. Reported cases were down about 21 percent, from 16,472 to 12,920, according to the Arizona Department of Health Services, but cases remained far higher than the 4,923 cases seen in 2002.
The California Department of Public Health says cases fell in several Central Valley counties last year, including Kern (27 percent), Kings (37 percent) and Fresno (32 percent), which have the highest incidence of coccidioidomycosis in the state.
Cases rose to varying degrees in more than a dozen counties, including Ventura (175 percent), Los Angeles (6 percent), Orange (39 percent) and Tulare (16 percent).
The report's findings are provisional as cases may be added or deleted from the data later, public health workers noted. Public health experts also have noted that research has shown that as many as nine out of 10 cases likely are undiagnosed or diagnosed as something else, meaning that cases of valley fever are vastly underreported.
Officials in several Central Valley public health departments and the Arizona Department of Health Services said they are seeing fewer confirmed cases of valley fever this year as well. But they cautioned that it's premature to draw conclusions and difficult to determine why cases fell.
"We still don't have all the critical things that allow us to predict with a reasonable level of certainty what the fall's going to look like," said Kirt Emery, Health Assessment and Epidemiology Program manager for the Kern County Public Health Services Department.
Climate could influence the number of cases, some experts said. But a couple valley public health officials said the exact impact of rain and wind on valley fever cases is still uncertain.
Construction, visitors from outside areas and growing education and awareness efforts could also play a part in the number of reported cases, said Clarisse Tsang, acting infectious disease epidemiology program manager for the Arizona Department of Health Services.
"To try to pinpoint what's going on with the decrease is really difficult to know," Tsang said.
In Kern County, the health department tallied 238 cases for the first nine weeks of the year, down from 480 cases in the same period in 2012 and 385 for that timeframe in 2011, Emery said. But the epidemiologist said those early numbers aren't enough to predict how the county's valley fever cases will trend throughout the year.
He pointed out that judging from the first couple months of 2012, one might have concluded that there would have been more cases than 2011, but that didn't bear out.
Fresno's monthly communicable disease reports tentatively show that valley fever cases tracked lower in the first three months of 2013 than during those months of the past two years. But then the number of cases reported in April almost doubled the tally for April 2012.
"Even if it's dropping, it's still a lot of cases," David Luchini, assistant director of the Fresno County Department of Public Health, said of the county's tally last year.
Luchini said he hopes efforts to mitigate valley fever at Pleasant Valley State Prison have helped Fresno's numbers. Last month, a federal receiver ordered inmates at high-risk of developing valley fever to be excluded from Pleasant Valley and another state prison.
"We're being optimistic (about the prison's efforts) but we want to see how this year goes and next year," Luchini said.
Whatever this year's valley fever cases add up to, the disease will remain a serious public health problem, public health administrators said.
"We don't want to be complacent. It is something that's endemic in our valley," Luchini said.
In fact, experts said the trends in valley fever cases highlight the need for more resources and better tools to track the prevalence of cocci.
"It is all the more reason to be aware and to think about (valley fever)," said Dr. Tom Larwood, a retired Bakersfield physician and valley fever advocate.
Larwood and Emery said a skin test would help identify how many people have been affected by the disease, not just those who were sick enough to visit a doctor and get tested. Overall, a vaccine would be the most important prevention tool, Emery said.
Kings County Health Officer Dr. Michael MacLean said one challenge is putting the disease in perspective.
Most people will not become gravely ill if they come down with valley fever, but that risk is always serious for groups inclined to develop serious valley fever, including those with compromised immune systems and African Americans.
"If you are at high risk for having complicated disease, you always need to be cautious because you are never 100 percent safe," MacLean said.
The Reporting on Health Collaborative involves The Californian, the Merced Sun-Star, Radio Bilingue in Fresno, The Record in Stockton, Valley Public Radio in Fresno and Bakersfield, Vida en el Valle in Fresno, the Voice of OC in Santa Ana and ReportingonHealth.org. It's an initiative of The California Endowment Health Journalism Fellowships at the University of Southern California's Annenberg School for Communication and Journalism.