Ten percent of adults hospitalized with pneumonia at a Phoenix hospital who were tested for Valley fever tested positive, and roughly a quarter of admitted pneumonia patients were never tested at all.
Mayo Clinic Phoenix researchers reviewed the medical records of 1,141 adults admitted with community-acquired pneumonia from November 2024 through October 2025. Of those patients, 76 percent were tested for Coccidioides infection, and 10 percent of the tested group had positive results. The findings were published in Open Forum Infectious Diseases and summarized by CIDRAP.
The denominator deserves emphasis before the number travels. Ten percent describes positivity among patients who were tested, not among everyone admitted with pneumonia. Since about a quarter were never tested, the study cannot say what proportion of all pneumonia admissions at that hospital involved the fungus.
Coccidioides was nonetheless the most commonly identified pathogen among these pneumonia patients, a notable result for an infection that requires a specific test to detect.
An Infection That Antibiotics Do Not Touch
The clinical stakes of a missed diagnosis explain why testing rates matter more than they might for other pathogens.
Valley fever is caused by inhaling spores of a soil-dwelling fungus endemic to the southwestern United States, parts of Washington state, and Central and South America. It is not bacterial. Standard antibiotics for pneumonia do nothing against it, so a patient treated empirically for bacterial pneumonia receives medication that cannot address the cause of their illness.
The consequences of that gap are practical. The authors note that missed diagnoses can prolong symptoms and hospitalization and can unnecessarily expose patients to antibacterial therapy or invasive diagnostic testing, which itself contributes to patient anxiety.
The diagnostic difficulty is that the symptoms do not distinguish it from other conditions. Common features include fever, cough, shortness of breath, rash, chest pain, weight loss, and fatigue. The researchers noted that these are often absent or resemble those of other causes of pneumonia, which slows diagnosis and treatment. Even otherwise healthy patients can develop severe disease.
Seasonal Peaks Visible in the Testing Data
The Mayo Clinic analysis captured a seasonal pattern that is useful for residents deciding when to raise the question.
Positive testing rates were highest in November and December 2024 and in October 2025, ranging from 13 to 21 percent, and again in March 2025 at 15 percent. That variation is consistent with the disease's known seasonality, which follows cycles of soil moisture and dust.
The study also separates those who are tested from those who test positive, and the two lists are not the same. Patients were most often tested if they had concerning chest radiographs, fatigue, fever, or shortness of breath. Those most likely to test positive were patients with a history of coccidioidomycosis and those with rash, night sweats, headache, or a high white blood cell count.
That mismatch is the practical finding. Clinicians were pattern-matching on general pneumonia severity while the features that actually predicted infection sat elsewhere. Given that Coccidioides accounts for an estimated 15 to 30 percent of community-acquired pneumonia in endemic areas such as Arizona, a substantial share of cases will not present with the features that prompted testing.
The Case for Testing Everyone Admitted
The authors call for testing all patients with community-acquired pneumonia, and they argue that this translates directly into how a hospital could operate differently.
When Coccidioides was identified early, the hospital length of stay was shorter than with pneumonia from other causes. The researchers noted that a shorter length of stay could be an institutional incentive to test all pneumonia patients for coccidioidal infection. In other words, identifying the correct pathogen sooner may get patients out of the hospital faster, which aligns the clinical interest with the operational one.
They also addressed the surveillance picture. The authors wrote that although the Centers for Disease Control and Prevention reports 10,000 to 20,000 coccidioidomycosis cases annually, the true incidence is likely much higher because of state-based differences in reporting practices and probable missed diagnoses.
That underdiagnosis sits alongside rising incidence. MedicalDaily has reported that CDC surveillance found Valley fever incidence approximately doubled across Arizona over roughly two decades, with Maricopa County remaining the hardest-hit region in the country.
The Question Southwest Residents Can Ask
For households in Phoenix, Tucson, and endemic areas of California, Nevada, New Mexico, Utah and Texas, the useful application of this study is one sentence in an exam room.
Anyone diagnosed with pneumonia in or after travel to an endemic region can ask whether they have been tested for Valley fever. The test is a blood test for antibodies, and it must be ordered specifically. Asking is particularly worthwhile for a patient whose symptoms are not improving after a course of antibiotics, a pattern most consistent with a fungal cause.
The people at highest risk of severe disease include those with weakened immune systems, organ transplant recipients, people taking immunosuppressive medication, people with diabetes, pregnant people in the later stages of pregnancy, and older adults. Certain populations also face an elevated risk of the infection spreading beyond the lungs.
Fungal infections have been drawing wider surveillance attention, including CDC work on invasive mold disease and its mortality, which MedicalDaily has covered. Most people with Valley fever recover without antifungal treatment, and the diagnosis does not automatically mean medication. What it does mean is an accurate explanation for a persistent illness and an end to ineffective antibiotic courses.
Several limits apply. This was a single-hospital record review at one Mayo Clinic facility over 12 months, and results may not generalize to other institutions or regions. It was retrospective, so it describes testing patterns rather than testing outcomes under a protocol. It did not measure whether patients who went untested were later diagnosed elsewhere. Readers should watch for whether Arizona institutions adopt universal testing protocols for admitted pneumonia patients, which would be the practical consequence of findings like these.
Key Questions Answered
What did the study find? Among 1,141 adults hospitalized with community-acquired pneumonia at Mayo Clinic Hospital in Phoenix from November 2024 through October 2025, 76 percent were tested for Coccidioides and 10 percent of those tested were positive.
Does that mean 10 percent of pneumonia patients had Valley fever? No. The figure describes positivity among patients who were tested. About a quarter were never tested, so the share among all admissions is unknown.
Why does testing matter? Valley fever is fungal. Standard pneumonia antibiotics do not treat it, so an untested patient may receive medication that cannot help.
What are the symptoms? Fever, cough, shortness of breath, rash, chest pain, weight loss and fatigue. These often resemble other causes of pneumonia, which is why diagnosis depends on a specific test.
Where is Valley fever common? The southwestern United States, parts of Washington state, and Central and South America. It causes an estimated 15 to 30 percent of community-acquired pneumonia in endemic areas of Arizona.
Who faces the greatest risk of severe illness? People with weakened immune systems, transplant recipients, people on immunosuppressive medication, people with diabetes, pregnant people later in pregnancy, and older adults.
What should a patient ask? Whether they have been tested for Valley fever, particularly if they live in or have traveled to an endemic area and are not improving on antibiotics.
