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Summer Weather Spreads a Silent Epidemic

Annie Hauser
Published: July 17, 2013

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There’s a “silent epidemic” — striking more and more people each year — sweeping the American Southwest, according to the U.S. Centers for Disease Control and Prevention.

Thanks to summer weather patterns, this year’s threat is likely just beginning.

The disease is coccidioidomycosis, or valley fever, an airborne fungal disease that is spread when microscopic spores in the soil take flight. In humans, the spores lodge in the lungs. In extreme cases, they spread to the bones, skin, eyes and even the brain, according to the CDC.

Last year, more than 20,000 cases were reported throughout the Southwest, mostly in California and Arizona, which resulted in 160 deaths. An estimated 150,000 more cases went undiagnosed because of mild symptoms or no symptoms at all, according to the CDC.

Summer temperatures and rainfall affect the growth and distribution of the fungus, according to CDC experts. Typically, infection rates spike when rainfall is followed by dry spells.

In Arizona, the Department of Health Services released a specific warning that dust storms and the summer weather pattern known as summer monsoons can stir up spores, according to the Associated Press.

“Contrary to popular belief, a monsoon is not a heavy, drenching downpour or an individual thunderstorm. Instead, it's a seasonal wind shift,” explained weather.com meteorologist Chris Dolce. In the Southwest, when these wind shifts are combined with heat, heavy thunderstorms, lightning and haboobs (dust storms) can result, Dolce said. 

"We've already seen monsoonal moisture in the Southwest this summer which has led to thunderstorms," Dolce said. "This includes a thunderstorm that brought blowing dust to the Phoenix metro." Typically, the monsoon peaks in intensity from middle July to middle August, but this can vary from year to year depending on the weather pattern, he added.

According to officials in Arizona, people should stay inside during dust storms to reduce their chance of infection.


The disease is named for San Joaquin Valley in central California, a cocci hot spot, according to the New York Times. In 2011, a federal judge ordered California to transfer about 2,600 inmates – including some with HIV and other immune-compromising diseases – just 90 miles north of the area. That year, 535 prisoners contracted the infection, the Times reported.

The high rate of infection among these immune-compromised prisoners underscores the complexities surrounding Valley Fever, according to the Times. Certain ethnic groups are more at risk, including African-Americans and Asians, particularly Filipinos, according to the CDC. Currently, it's not known which genes affect the expression of the gene.

No vaccine is available for Valley Fever. Although many cases don’t require treatment, many physicians will prescribe antifungal medications to prevent complications. If you live or visit an area with a high infection rate and experience flu-like symptoms for a week or more, visit a doctor coccidioidomycosis test and treatment, the CDC advises.

MORE: Diseases You Can Have - and Not Know It!

When an outbreak of an infectious disease occurs – thinks SARS or the new MERS virus – human carriers who show no outward signs of the disease spread the infection. Click through to find out which other diseases can be silent, asymptomatic killers.


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