DAVIS, Calif. — Taking count of the worst-ever epidemic of the strange airborne disease called valley fever, health authorities report that at least 1,000 people in three counties took ill with severe flu-like symptoms and nine died in the final months of last year.
In all, the disease, found most commonly in the San Joaquin Valley and arid sections of the Southwest, struck almost 2,000 people across California last year, more than four times the 441 cases reported in 1990.
"It is an epidemic, and a historic epidemic in terms of its size," said Royce Johnson, associate professor of medicine at UCLA and chief of infectious disease control at Kern Medical Center.
Valley fever is not as serious a killer as influenza, which was blamed for 155 California deaths in 1990, but the striking rise in cases prompted a joint effort by the federal Centers for Disease Control, the University of California and the state Department of Health Services to determine the cause of the scourge.
And the experts do have a suspect: the heavy rains last March that helped ease the drought. The wet soil evidently nurtured a bumper crop of the fungus that causes the disease.
After the valley soil baked dry under the sun, the culprit spores-- Coccidioides immitis --took to the air in the strong wind and dust storms of autumn and winter. Residents inhaled the spores and the fungus bloomed in their lungs in the form of the disease, also known as coccidioidomycosis.
Dr. Demosthenes Pappagianis, a UC Davis medical professor who has devoted 40 years to studying valley fever, said he suspects that some travelers from other areas who were on Interstate 5 in dust storms after Thanksgiving and Christmas contracted the disease. But the state Department of Health Services has not yet found abnormal numbers of cases outside the San Joaquin Valley.
The last major outbreak of valley fever followed a December, 1977, Kern County dust storm that sent spores far into Northern California. People in Redding and Sacramento were among the 379 cases after that storm, and a gorilla at the San Francisco Zoo died of the disease.
The center of the new epidemic is Kern County, the perennial leader in valley fever cases. The Kern County health department reported 1,181 cases and nine deaths in 1991, with most of the fatalities taking ill and dying in the final four months of the year. In the first three weeks of January, another 75 cases were diagnosed. In 1990, a more average year, Kern County reported 240 cases and three deaths.
To the west, in San Luis Obispo County, where five annual cases is a high number, two people have died and 33 have been found to have the disease since October, health officials said. In Tulare County, north of Kern, there were 204 cases last year, compared to 81 in 1990, Pappagianis said.
"The numbers will undoubtedly increase because some of the people who got their infections in 1991 have not been diagnosed yet," said Pappagianis.
In Kern County, Johnson said the 1,181 confirmed cases are "the tip of the iceberg." He estimated that as many as 8,000 people were infected. But half the people who become infected usually show little or no symptoms, and some seek no medical help.
In one week in November, at the peak of the epidemic, 134 cases were diagnosed in Kern County. That came three weeks after an October wind flurry that forced closure of the umbrella exhibit by the artist Christo along the Kern County-Los Angeles County line.
Kern residents long ago learned that if they venture to such sites as Shark Tooth Mountain northeast of Bakersfield and stir up the dust in search of fossils from an ancient sea, chances are they will come down with valley fever. The Health Department used to post warning signs around the mountain.
The reason that Kern County is a valley fever hotbed is not well understood. But the fungus, unlike many microorganisms, is known to thrive in Kern County's salty, alkaline soil. The fungus also needs the mild winters common in Kern County and other arid areas where the disease occurs.
Many people who grow up in the San Joaquin Valley contract the disease at a young age, when the symptoms generally are minor. Samples have shown that as many as half of longtime residents have antibodies proving they have been infected.
As the Central Valley population grows, Pappagianis predicts, new residents are likely to come into contact with the fungus, which could make it a greater problem.
"As new people come into the valley, they're going to be susceptible," he said, sitting in a UC Davis office decorated with a photo of the fungus.
Across the hallway, his medical lab assistants tested serum samples sent in by the hundreds from doctors around the state.