Employees at Avenal and Pleasant Valley state prisons near Fresno appear more likely to contract valley fever than adults in the surrounding population, the report by the National Institute for Occupational Safety and Health said.
The institute found that the employee deaths and illnesses occurred between January 2009 and last June.
The state requested the report after nearly three-dozen inmate deaths and hundreds of hospitalizations at the prisons were blamed on the fungus that causes the illness known as valley fever.
A federal judge ordered the state to move nearly 2,600 inmates to other prisons last fall because those inmates were deemed to be more susceptible to the fungus, which grows naturally in the soil in the Central Valley and other dry locations such as Arizona and Mexico.
The inmate deaths and illnesses are being separately reviewed by the federal Centers for Disease Control, which has yet to release its findings.
Blacks, Filipinos and inmates suffering from diabetes and HIV are among those thought to be most prone to valley fever and were ordered out of the prisons.
The report by the affiliated occupational safety institute focuses on employee illnesses.
Officials with the California Department of Corrections and Rehabilitation, with the union that represents most prison guards and with the federal court-appointed official who runs prison medical care all said they were reviewing the report and had little immediate comment.
Pleasant Valley State Prison in Fresno County had 3,358 inmates and more than 1,300 guards and other employees last May. The institute confirmed 65 valley fever cases among the prison's employees over the 3 1/2-year period of its study, including two employee deaths.
That equates to an average rate of 1,039 cases per 100,000 individuals, higher than the general rate of infection of 40 cases per 100,000 among the non-inmate adult population in Fresno County, the report says, though it cautions that there can be no direct comparison because of differences in the populations and the reporting of the illness.
Avenal State Prison in Kings County had 4,538 inmates and more than 1,500 employees last May. The institute confirmed 38 valley fever cases there, with one death. It had an average rate of 511 cases per 100,000, higher than the average of 110 cases per 100,000 adults in Kings County.
Researchers couldn't determine if the prison employees contracted the disease at work or outside of work, and said most were likely exposed to the fungus on and off the job.
The state thwarted a previous study by the Centers for Disease Control in 2008 and decided against spending $750,000 for improvements at one of the prisons in 2007 because of the high cost. Yet three experts appointed by the federal judge found last year that the state spends more than $23 million annually to treat inmates hospitalized with valley fever.
The fungus usually produces no symptoms, but in about 40 percent of cases it causes mild to severe flu-like symptoms or more serious infections. Valley fever can spread to the brain, bones, skin and eyes, leading to blindness, skin abscesses, lung failure and death.
In California, rates of reported fever cases increased more than six-fold over the past decade, from about 700 in 1998 to more than 5,500 cases reported in 2011, according to the CDC.