Phoenix-area residents are now in the peak months for Valley fever infection, and new federal data confirm the threat is worse than ever. A landmark study published February 19, 2026 in the CDC's Morbidity and Mortality Weekly Report confirmed that coccidioidomycosis — the fungal lung disease commonly known as Valley fever — has approximately doubled in incidence across Arizona between 2005 and 2022, with Maricopa County (Phoenix metro) remaining the single hardest-hit region in the country.
June through July is the highest-risk period for Valley fever infections in Arizona, according to the University of Arizona, making this week the beginning of what researchers and health officials consider the most dangerous stretch of the year for exposure.
The Phoenix metro reported 12,522 confirmed Valley fever cases in 2024 — a 42 percent increase over the 8,841 cases reported in 2023 for the same period, according to Outbreak News Today tracking of Arizona Department of Health Services data. Nationally, reported cases reached 22,244 in 2024, up from 16,746 the year prior.
A Disease That Is Expanding Its Footprint — and Still Being Missed
The most alarming finding in the 2026 MMWR report is not the Phoenix numbers. It is what is happening elsewhere. While the majority of Arizona's Valley fever cases remain concentrated in the southwestern Sonoran Desert region, the largest relative increases in incidence are occurring in the state's historically low-risk northern Plateaus and Mojave Desert regions — areas where physicians are far less likely to consider Valley fever as a possible diagnosis and where awareness among the general public is limited.
The CDC MMWR study attributes this geographic expansion to a combination of factors including population growth in previously rural areas, increased outdoor construction and soil disturbance activity, and climate-related shifts in the Coccidioides fungus's habitat range. Valley fever grows in soil following heavy rainfall; when conditions become hot and dry, the fungal spores become airborne and are inhaled by anyone working or living in affected areas.
Valley fever is a disease with a severe misdiagnosis problem. Its early symptoms — fever, fatigue, cough, shortness of breath, chest pain, headache, and rash — closely mimic influenza, bacterial pneumonia, and other common respiratory illnesses. The OSHA factsheet notes that patients are routinely treated with antibiotics that have no effect against fungi, losing critical weeks or months before the correct diagnosis is made.
Studies suggest the true number of Valley fever cases in the United States is 10 to 18 times higher than official reports, because most mild cases are never tested.
Who Is at Risk and What Residents Should Do
According to the Maricopa County Health Department, certain groups are at significantly elevated risk for severe Valley fever, including people who are Black or Filipino (due to genetic factors that may predispose them to disseminated disease), people with diabetes or a weakened immune system, adults 60 and older, pregnant women, and individuals whose work or recreation involves disturbing desert soil.
This includes construction workers, agricultural workers, landscapers, archaeological diggers, military personnel training in desert areas, and people who ride ATVs, mountain bikes, or 4x4 vehicles in desert terrain.
Valley fever cannot be transmitted from person to person. It is not contagious. The only route of infection is inhaling airborne fungal spores.
A small percentage of cases — particularly among immunocompromised individuals — progress to disseminated coccidioidomycosis, a severe form in which the fungus spreads from the lungs to bones, joints, skin, or the brain, causing fungal meningitis that can be fatal even with treatment.
Phoenix-area residents who develop persistent flu-like symptoms, especially a prolonged cough or chest pain that does not respond to antibiotics, should specifically ask their physician about testing for Valley fever. The standard blood test (coccidioidin skin test or serology) can confirm or rule out the diagnosis quickly.
Frequently Asked Questions
Q: What is Valley fever?
A: Valley fever (coccidioidomycosis) is a lung infection caused by the fungus Coccidioides, which lives in the soil in the southwestern United States. It spreads when airborne spores are inhaled after soil is disturbed.
Q: When is Valley fever season in Phoenix?
A: The highest-risk period in Arizona is June through July and again from October through November, when heat and dry conditions disperse spores into the air.
Q: Is Valley fever contagious?
A: No. Valley fever cannot spread from person to person. The only route of infection is breathing in airborne fungal spores from disturbed soil.
Q: What are Valley fever symptoms?
A: Fever, fatigue, cough, shortness of breath, chest pain, headache, and rash. Symptoms often resemble a bad cold or flu and do not respond to antibiotics.
Q: Who is most at risk for severe Valley fever?
A: People who are Black or Filipino, individuals with diabetes or weakened immune systems, adults over 60, pregnant women, and outdoor workers in endemic areas.
