Among adults hospitalized for community-acquired pneumonia at an Arizona hospital, Valley fever was the most commonly identified cause among those tested. Mayo Clinic Phoenix researchers reviewed records for 1,141 patients admitted over a twelve-month period and found 76 percent were tested for Coccidioides, and 10 percent of those tested were positive.
The corollary is the part worth sitting with. Roughly a quarter of pneumonia patients in a region where the fungus is endemic were never tested for it.
That matters because Valley fever is not treated the same way as bacterial pneumonia. It is a fungal infection, and antibacterial drugs do nothing against it.
The Diagnosis That Depends on Someone Asking
Coccidioidomycosis, commonly called Valley fever, is caused by inhaling spores of Coccidioides species, which live in soil across the southwestern United States and are also found in Washington state and parts of Central and South America. The fungus grows in soil after rain and disperses into the air when conditions turn hot and dry or when soil is disturbed.
Symptoms overlap almost entirely with other causes of pneumonia, including fever, cough, shortness of breath, rash, chest pain, weight loss, and fatigue. Nothing announces a fungal cause, and coccidioidomycosis accounts for an estimated 15 to 30 percent of community-acquired pneumonia in the Phoenix and Tucson metropolitan areas.
In the Mayo review, patients were most often tested when they had concerning chest radiographs, fatigue, fever, or shortness of breath. Those most likely to test positive included patients with a history of coccidioidomycosis and those with rash, night sweats, headache, or a high white blood-cell count.
Positivity followed a seasonal pattern, peaking in November and December and again the following October at 13 to 21 percent, with a further rise in March. The authors called for testing all pneumonia patients in endemic areas, noting in their published analysis that missed diagnoses "can potentially prolong symptoms and hospitalization" and expose patients to unnecessary antibacterial therapy or invasive testing. When the infection was identified early, hospital stays were shorter.
An Ordinary Activity as the Exposure Route
What makes Valley fever unusual among serious infections is how mundane the exposure is. Digging in a garden, working a construction site, driving on a dirt road, or simply being outdoors on a dusty day can be enough.
The fungus does not spread between people. There is no contagion to trace, no isolation to enforce, and no vaccine.
Most infections resolve on their own as a pneumonia-like illness. But roughly 5 to 10 percent of people who get Valley fever develop serious or long-term problems in the lungs, and in about 1 percent the infection spreads beyond the lungs to skin, bone, joints, or the central nervous system, with chronic consequences. Severe pulmonary disease and dissemination are more likely in older people and those who are immunocompromised.
Treatment depends on severity and immune status, and often involves three to six months of oral antifungal therapy such as fluconazole or itraconazole. Chronic or disseminated infections can require a year or more of treatment.
Where the Fungus Is Spreading
Arizona and California report more than 95 percent of U.S. cases, but the geography within those states is shifting. A CDC analysis published earlier this year found that Arizona's incidence approximately doubled between 2005 and 2022.
The more striking finding was regional. While the great majority of cases still come from the southwestern Sonoran Desert region, including Maricopa, Pima, and Pinal counties, the largest relative increases occurred in the historically low-incidence northern Plateaus and Mojave Desert regions. During 2020 through 2022, incidence in the Plateaus region was 6.61 times that of 2005 through 2007, and in the Mojave Desert region, 4.50 times.
The CDC report attributed the broader southwestern rise to increasing aridity, warming temperatures, and precipitation volatility, and described the causes of the regional shift within Arizona as likely multifactorial. Nevada, New Mexico, and Utah also report cases, with smaller numbers further north and east.
Reported cases understate the burden. Around 20,000 are reported each year nationally, while the CDC estimates the true number of symptomatic cases at roughly 206,000 to 360,000, or 10 to 18 times that figure.
Raising It with a Clinician
For residents of and visitors to endemic areas, the useful action is knowing how to ask. Anyone with a persistent cough, fever, and fatigue that is not improving, particularly after exposure to dust outdoors, can ask directly whether Valley fever testing is appropriate.
That request is especially worth making outside the traditional high-incidence counties, where clinician awareness may be lower even as incidence rises. It also matters for travelers who develop symptoms after returning home, since a clinician elsewhere may not consider a southwestern fungal infection at all. The CDC publishes a clinical overview that providers can consult.
People with weakened immune systems, those who are pregnant, and people with diabetes face a higher risk of severe or disseminated disease and warrant a lower threshold for testing.
Prevention options are limited but real. CDC prevention guidance notes that dust control measures and use of respirators in high-risk situations, such as heavy soil disturbance, may reduce exposure where feasible.
Symptoms that warrant prompt evaluation include difficulty breathing, chest pain, coughing up blood, severe headache with neck stiffness, or new skin lesions or joint swelling in someone with a known infection.
Key Questions Answered
What did the hospital study find? Of 1,141 adults hospitalized for community-acquired pneumonia in Arizona, 76 percent were tested for Coccidioides and 10 percent of those tested were positive, making it the most commonly identified pathogen.
Why does testing matter so much? Valley fever is fungal. Antibacterial drugs do not treat it, so an untested patient may receive weeks of ineffective therapy while the actual infection continues.
How do people get infected? By inhaling spores from soil, often when soil is disturbed by digging, construction, driving on dirt roads or wind. It does not spread between people.
How serious is it? Most infections resolve on their own. About 5 to 10 percent of people develop serious or long-term lung problems, and in roughly 1 percent the infection spreads beyond the lungs.
Where is the risk? Arizona and California report more than 95 percent of U.S. cases, with Nevada, New Mexico and Utah also affected. Arizona incidence roughly doubled between 2005 and 2022.
How many cases actually occur? About 20,000 are reported yearly, but the CDC estimates the true burden at 206,000 to 360,000 symptomatic cases, meaning most go undiagnosed.
What should someone ask a clinician? Whether Valley fever testing is appropriate for a cough and fever that are not improving, especially after dusty exposure or travel to the Southwest.
