Mar 28, 2013 (CIDRAP News) – Coccidioidomycosis, or valley fever, a fungal infection that causes influenza-like symptoms and often leads to hospitalization, has increased "dramatically" in the US Southwest in recent years, the Centers for Disease Control and Prevention (CDC) reported today.
The five affected states that report cases—Arizona, California, Nevada, New Mexico, and Utah—recorded just 2,265 in 1998, or 5.3 per 100,000 population. By 2011 the number reached 22,401 cases, or 42.6 per 100,000, the CDC reported in the Mar 29 issue of Morbidity and Mortality Weekly Report (MMWR).
Reasons for the increase are unclear, but possible factors include environmental and population changes, evolving surveillance methods, and greater awareness of the illness, the CDC said. Despite the rising number of cases, it appears that mortality rates have stayed about the same.
"Valley fever is causing real health problems for many people living in the southwestern United States," said CDC Director Tom Frieden, MD, MPH, in a press release. "Because fungus particles spread through the air, it's nearly impossible to completely avoid exposure to this fungus in these hardest-hit states. It's important that people be aware of valley fever if they live in or have traveled to the southwest United States."
Valley fever is caused by inhaling the soil-dwelling fungus Coccidioides, which is found in dry areas of Mexico and Central and South America as well as the southwestern United States, the CDC said.
Not everyone who is exposed gets sick. For those who do, the infection typically causes a self-limiting flu-like illness that can last weeks or months. Some people suffer severe or chronic lung disease. The infection spreads to other parts of the body in less than 1% of cases.
Seventy-five percent of patients are sick enough to miss work or school for about 2 weeks, and more than 40% need hospitalization, the CDC said. Hospitalization costs average about $50,000, according to the press release.
From 1998 through 2011, 28 states and Washington, DC, reported a total of 111,717 coccidioidomycosis cases. Arizona alone had 66% of those, while California had 31%. In the five southwestern states in which the fungus is endemic, cases increased steadily over the 14 years, except for decreases in 2007 and 2008.
The jumps in the last 3 years of the period were particularly sharp: from 7,464 in 2008 to 12,868, 16,664, and 22,401 in 2009, 2010, and 2011.
The annual rates of increase averaged to about 16% for Arizona and 13% for California, with adjustments for changes in population size and the age and sex distribution of cases, the CDC said. Both rates were significant.
The incidence was highest in people age 60 and older, except in California, where those 40 to 59 were hardest hit. In Arizona in 2011 the incidence in 60- to 79-year-olds was 381.1 per 100,000; it was slightly higher in those 80 and older.
While cases have clearly increased, a study published last year found that coccidioidomycosis mortality rates stayed fairly stable at about 0.6 per 1 million person-years between 1990 and 2008, according to the report.
The upward trend in valley fever cases "could be related to changes in weather, which could impact where the fungus grows and how much of it is circulating; higher numbers of new residents; or changes in the way the disease is detected and reported to the states or CDC," the agency press release said.
Soil disturbances caused by construction and other human activities are another possible contributing factor, the MMWR article says.
Greater awareness of the disease might have triggered increased diagnostic testing and reporting, the CDC said. The disease is estimated to be the cause of 15% to 29% of community-acquired pneumonia cases in areas where Coccidioides is highly endemic, but a 2006 study suggested that the illness is "greatly underreported."
"Doctors and patients should know that the symptoms of valley fever are very similar to flu or pneumonia symptoms and a lab test is the only way to tell if an illness is valley fever or not," the press release states. "Not everyone who gets Valley Fever needs treatment, but for people at risk for the more severe forms of the disease, early diagnosis and treatment is important. The best way to treat Valley Fever still needs to be studied, especially with the number of cases continuing to rise."
The MMWR article says the role of antifungal treatment for valley fever is controversial, but it is recommended for certain groups. Although no proven preventive measures are available, the CDC suggests that people in affected areas should consider trying to reduce their exposure to dusty air, which may contain the fungal spores.
CDC. Increase in reported coccidioidomycosis—United States, 1998-2011. MMWR 2013 Mar 29;62(12):217-21 [Full text]
Mar 28 CDC press release