Ten percent of adults hospitalized with community-acquired pneumonia in Phoenix who were tested for Valley fever tested positive, and roughly one in four such patients was never tested at all, according to a review of a year of hospital records by Mayo Clinic researchers.
The analysis covered 1,141 adults admitted to Mayo Clinic Hospital in Phoenix with community-acquired pneumonia between November 2024 and October 2025. Of those, 76 percent received testing for Coccidioides, the soil fungus that causes the infection, and 10 percent of the tested group had positive results. The findings were published in Open Forum Infectious Diseases.
The authors called for testing every community-acquired pneumonia patient in the endemic region. Their argument is practical rather than theoretical: when the infection was identified early, the hospital length of stay was shorter than for pneumonia from other causes.
The Diagnostic Problem Sits in the Symptoms
Valley fever presents like other pneumonia. Fever, cough, shortness of breath, chest pain, fatigue and weight loss are all common, and none of them distinguishes a fungal infection from a bacterial one at the bedside. The CDC's clinical overview notes that roughly 40 percent of infected people develop symptoms, typically one to three weeks after exposure, and that the illness is often clinically indistinguishable from pneumonia caused by other pathogens.
That overlap is the entire difficulty. Without a specific test, a patient with Valley fever looks like a patient who needs antibiotics, and antibiotics do nothing against a fungus. The Mayo authors wrote that missed diagnoses can prolong symptoms and hospitalization while unnecessarily exposing patients to antibacterial therapy or invasive diagnostic testing.
In the Phoenix cohort, Coccidioides was the most commonly identified pathogen among pneumonia patients. Positivity followed the disease's known seasonality, peaking in November and December 2024 and October 2025, at 13 to 21 percent, and reaching 15 percent in March 2025. Clinicians tested most often when a patient had a concerning chest radiograph along with fatigue, fever or shortness of breath. The patients most likely to test positive were those with a prior history of the infection and those presenting with rash, night sweats, headache or a high white blood cell count.
As the researchers put it in a summary reported by CIDRAP, "A shorter LOS could be an institutional incentive to test all patients with CAP."
Where the Fungus Actually Lives
Coccidioides is endemic to the southwestern United States, parts of Washington state, and Central and South America. Arizona and California account for the overwhelming majority of reported U.S. cases.
In endemic areas such as Arizona, the fungus is estimated to cause 15-30% of community-acquired pneumonia.
The infection spreads by inhalation of airborne spores released when contaminated soil is disturbed, whether by small-scale activity such as construction or excavation or by large-scale events such as dust storms. It does not spread from person to person, and most people who inhale spores either never become sick or have an illness that resolves without treatment.
National case counts almost certainly understate the burden. The Mayo authors noted that while the CDC reports 10,000 to 20,000 cases annually, the true incidence is likely much higher because of state differences in reporting practices and probable missed diagnoses.
The Groups Facing the Highest Stakes
Severe and disseminated disease, in which the fungus spreads beyond the lungs to bones, joints, skin, or the central nervous system, is uncommon but serious and can require lifelong treatment.
Risk concentrates among people with weakened immune systems, including those with HIV, organ transplant recipients, and people taking corticosteroids or other immunosuppressive medications. People with diabetes face an elevated risk, as do pregnant people. CDC surveillance has identified Black race and Filipino ethnicity among documented risk factors for severe disease, and the agency lists host factors in specific racial and ethnic groups as an open research question.
Occupational exposure matters. Construction workers, agricultural workers, archaeologists, and military personnel training in desert conditions routinely encounter disturbed soil.
Newcomers to endemic regions and travelers are a distinct group because a clinician outside Arizona or California may never consider the diagnosis in a patient who returned home with a lingering cough.
The Practical Ask for Patients in Endemic Regions
The single most useful thing a patient in an endemic area can do is name the exposure. Anyone who lives in or has recently visited the endemic Southwest and develops a cough, fever, fatigue or shortness of breath that has not resolved in one to two weeks can tell the clinician where they live or traveled and ask directly whether Valley fever testing is appropriate.
That request is reasonable. Serologic testing is standard and widely available in endemic regions, and the Mayo data suggest the yield is meaningful.
Patients should not stop prescribed antibiotics on their own, and should not assume a pneumonia diagnosis is wrong. Both bacterial pneumonia and Valley fever are real possibilities in the same patient population, and the point of testing is to distinguish them rather than to substitute one assumption for another.
Anyone in a higher-risk group who develops respiratory symptoms after significant dust exposure should raise it with a clinician sooner rather than later. Severe symptoms including difficulty breathing, chest pain, confusion, or a rapidly worsening condition warrant urgent evaluation regardless of suspected cause.
Prevention options are limited and imperfect. Staying indoors during dust storms, keeping car windows closed in dusty conditions, and wetting soil before digging can reduce exposure. There is no vaccine, though developing one remains an active research goal.
MedicalDaily previously reported on CDC data showing Valley fever incidence roughly doubled across Arizona over recent decades. This new work addresses a different link in the chain: whether cases that reach a hospital are correctly identified upon arrival.
Key Questions Answered
What did the study find? Among 1,141 adults hospitalized with community-acquired pneumonia at Mayo Clinic Hospital in Phoenix over one year, 76 percent were tested for Coccidioides, and 10 percent of those tested were positive. About 24 percent were never tested.
What is Valley fever? Coccidioidomycosis is a lung infection caused by inhaling spores of the Coccidioides fungus, which lives in soil across the southwestern United States and parts of Latin America. It does not spread between people.
Why does testing matter if many cases resolve on their own? Because untested patients may receive antibiotics that cannot treat a fungal infection, may undergo unnecessary invasive testing, and may have a longer hospital stay. The study found shorter stays when the infection was identified early.
What symptoms should prompt a test request? Cough, fever, fatigue, shortness of breath or chest pain that has not improved within one to two weeks, in someone who lives in or recently visited the endemic Southwest.
Who faces the greatest risk of severe illness? People with weakened immune systems, people with diabetes, pregnant people, and workers with heavy dust exposure. CDC surveillance has also identified Black race and Filipino ethnicity as risk factors for severe disease.
Can I prevent it? Only partially. Avoiding dust storms, keeping car windows closed in dusty conditions, and wetting soil before digging reduce exposure. No vaccine exists.
Should I stop antibiotics if I suspect Valley fever? No. Do not stop a prescribed medication without speaking to a clinician. Ask about testing so the diagnosis can be established rather than assumed.
