PHOENIX — A landmark federal surveillance study published in the CDC's Morbidity and Mortality Weekly Report on February 19, 2026 has confirmed what public health officials in Arizona have been warning about for years: Valley fever (coccidioidomycosis), the fungal lung disease caused by inhaling soil-borne Coccidioides spores, has approximately doubled in incidence across Arizona between 2005 and 2022 — with the most alarming new finding being that the disease is aggressively expanding into regions of the state where it was historically rare. The Phoenix metropolitan area — which sits in Maricopa County at the heart of Arizona's Sonoran Desert region — remains the single hardest-hit area in the country, accounting for the majority of a statewide total that reached 12,522 confirmed cases in 2024 alone.

That 2024 figure represented a 42% increase over the same period in 2023, when 8,841 cases were reported. And the national picture is equally alarming: the U.S. is currently tracking on pace to surpass last year's total in the first half of 2026. In 2023, states reported 21,037 confirmed cases nationally — the highest annual total since modern surveillance began. Valley fever is responsible for an estimated 15% to 30% of all community-acquired pneumonias diagnosed in the Phoenix and Tucson metro areas. The burden falls most heavily on the elderly, people with diabetes, Black and Filipino patients, and those with weakened immune systems.

What Is Valley Fever and How Do You Get It?

Coccidioidomycosis — the medical name for Valley fever — is caused by inhaling microscopic spores of the Coccidioides fungus, which lives in the soil of arid and semi-arid regions. In Phoenix and the surrounding Sonoran Desert, the fungus is endemic: it is a permanent feature of the soil, concentrated in undisturbed areas, and released when that soil is disturbed by wind, construction, farming, off-road vehicle activity, or even a garden shovel.

Most people who inhale Coccidioides spores never become sick, or experience only mild flu-like symptoms — fatigue, cough, fever, and body aches — that resolve on their own within weeks. But approximately 5% to 10% of infected individuals develop more serious illness. A small percentage, particularly those with compromised immune systems or diabetes, progress to severe or disseminated coccidioidomycosis, in which the fungus spreads from the lungs to other organs: bones, joints, the skin, and in the most devastating cases, the brain and meninges, causing fungal meningitis that can be fatal even with treatment.

Valley fever is consistently misdiagnosed. Because its symptoms mimic those of influenza, bacterial pneumonia, and other common respiratory illnesses, patients are routinely treated with antibiotics that have no effect on fungi — losing critical weeks or months before the correct diagnosis is made. Studies suggest that the true number of Valley fever cases in the United States is 10 to 18 times higher than the number officially reported, because the disease is simply not tested for in most clinical settings outside the endemic regions.

The MMWR Data: A Doubling Incidence and a Geography That Is Expanding

The February 2026 MMWR report analyzed surveillance data reported to the Arizona Department of Health Services from 2005 through 2022, dividing the state into six distinct ecological regions. The core finding is stark: while the Sonoran Desert region — which includes Maricopa County and Phoenix — accounts for more than 95% of all Arizona cases, the largest relative increases in incidence are occurring in regions where Valley fever was historically uncommon: the northern Plateaus and Mojave Desert. These are areas where healthcare providers, patients, and even some physicians may not think to consider Valley fever when evaluating respiratory illness — creating fertile ground for the diagnostic delays that allow the disease to progress to severe or disseminated forms.

The drivers of expansion are well established in the scientific literature. Valley fever thrives in conditions of increasing aridity, warming temperatures, and precipitation volatility — exactly the conditions that climate projections forecast for the American Southwest over the coming decades. Construction activity that disturbs previously untouched soil releases concentrated spore clouds. Phoenix, one of the fastest-growing major metropolitan areas in the country, has seen decades of relentless residential and commercial development spreading into desert regions previously undisturbed.

Local Data: 709 Hospital Visits in Texas — And Valley Fever Isn't Even Reportable There

The Arizona numbers are sobering, but they represent only a fraction of the national picture. In Texas — which borders the Valley fever endemic zone and contains an estimated 96-county region of endemic soil in West Texas — Valley fever is not a reportable disease, meaning the state has no mandatory system for tracking cases. Despite this, a CDC-published study found that 709 Valley fever-related inpatient and outpatient hospital visits occurred in Texas in a single year, with prevalence of 3.17 cases per 100,000 total hospital visits. Non-Hispanic Black and Hispanic patients had the highest documented prevalence.

Nationally, the modeling is even more troubling: researchers estimate that Valley fever causes between 18,000 and 28,000 hospitalizations annually and between 700 and 1,100 deaths — numbers that are largely invisible because the disease is attributed to other causes, unreported, or never correctly diagnosed. CIDRAP noted this year that the US is tracking toward surpassing last year's record case total before the year is even half over.

What Phoenix-Area Residents Must Know Right Now

Summer in Phoenix brings a particular combination of environmental conditions — hot, dry air; dust storms (haboobs) that can move millions of cubic feet of soil; and active construction on dozens of ongoing development projects — that maximizes Valley fever spore exposure risk. These are the precautions Maricopa County health officials recommend:

• Stay indoors during dust storms. When visible clouds of dust move through the Phoenix metro, the spore load in outdoor air spikes dramatically. Keep windows and doors closed and avoid unnecessary outdoor activity.

• Wear an N95 or higher-rated mask when doing outdoor work that disturbs soil: gardening, landscaping, construction, or even hiking in dusty areas. Standard surgical masks do not filter particles small enough to block Coccidioides spores.

• If you develop a persistent cough, fatigue, fever, or shortness of breath that does not resolve within 1–2 weeks, tell your doctor you live in or recently visited Arizona and ask specifically to be tested for Valley fever. Do not accept a diagnosis of "just a cold" without ruling out coccidioidomycosis.

• People with diabetes, HIV/AIDS, cancer, or those taking immunosuppressive medications face dramatically elevated risk of severe disease and should discuss preventive strategies with their physician.

The Maricopa County Department of Public Health Valley Fever page provides current advisories and educational resources for residents.

Conclusion: Valley Fever Is a Looming Major Public Health Crisis — Being Treated Like a Minor Inconvenience

A fungal disease that causes 700 to 1,100 deaths annually, that mimics COVID, influenza, and bacterial pneumonia, that is almost certainly under-diagnosed by a factor of 10 to 18 — and that is now expanding geographically into regions where physicians have never been trained to look for it — deserves treatment as a major public health priority. Instead, Valley fever receives a fraction of the research funding, clinical attention, and public awareness campaigns devoted to far less prevalent infectious diseases.

The February 2026 MMWR report is a federal surveillance document, not a headline. But its data tell a story that every Phoenix-area resident, every physician in the Southwest, and every public health official tracking emerging infectious disease threats should read carefully. The Coccidioides fungus has been in the Arizona soil for millennia. It is not going away. What is changing — and what we must respond to — is how far it is spreading, how many people it is reaching, and how unprepared our healthcare system remains to catch it.

▌ RELATED ON MEDICALDAILY.COM

→ Valley Fever: The Fungal Lung Disease Spreading Across America's Southwest

→ CDC Confirms Valley Fever Cases Are 10 to 18 Times Higher Than Reported

→ The Dust Storm Danger: How Haboobs Drive Valley Fever Outbreaks in Phoenix

→ Misdiagnosed for Months: Valley Fever Patients Share Their Stories