Valley Fever (Coccidioidomycosis)
A fungal lung infection caused by breathing Coccidioides spores from soil and dust, most often in parts of the southwestern United States and south-central Washington.
What causes Valley Fever (Coccidioidomycosis)?
Valley fever is caused by Coccidioides immitis or Coccidioides posadasii. Infection usually follows inhalation of airborne spores after soil or dust is disturbed. It does not ordinarily spread from person to person or between people and animals.
Symptoms and what to notice
Fatigue, cough, fever, headache, shortness of breath, night sweats, muscle or joint pain, and a rash. Many exposed people have no symptoms, while others develop a pneumonia-like illness.
How long can it last?
Symptoms generally begin 1 to 3 weeks after exposure and may last from a few weeks to several months. Severe pulmonary or disseminated infections can continue for months or years.
How serious is Valley Fever (Coccidioidomycosis)?
About 5% to 10% of infections develop serious or long-term lung problems, and about 1% disseminate to areas such as skin, bones, joints, or the central nervous system. Untreated coccidioidal meningitis is fatal.
Treatment and management
Many mild infections improve without antifungal medicine. Higher-risk, severe, chronic, or disseminated disease may require fluconazole, itraconazole, amphotericin B, hospitalization, or surgery. Coccidioidal meningitis generally needs lifelong antifungal treatment.
Vaccine: who and when?
No FDA-approved human vaccine is available for Valley fever in the United States. Vaccine research is ongoing. Prevention focuses on reducing exposure to contaminated dust, especially for people at increased risk of severe disease.
Cost note: No vaccine price applies because no human Valley fever vaccine is currently available. Evaluation, testing, imaging, antifungal treatment, and specialist-care costs vary by provider, insurance, and disease severity.
Trusted source
Patient cost varies by insurance, provider, location, and eligibility. Coverage and public-health access differ, so listed prices are examples rather than guaranteed patient prices. This page is for general education and does not replace individualized medical advice, diagnosis, vaccination assessment, or treatment.
Valley Fever (Coccidioidomycosis): History, Symptoms, Causes, Treatment, Prevention, and Vaccine Information
Valley fever, medically known as coccidioidomycosis, is a fungal infection caused by breathing microscopic spores of Coccidioides fungi from contaminated soil and dust.
The disease occurs primarily in dry regions of the southwestern United States, particularly Arizona and California, as well as parts of Mexico, Central America, and South America. The fungus has also been identified in parts of Washington state, showing that its geographic range is broader than once believed.
Most people who breathe in Coccidioides spores never develop noticeable illness. CDC estimates that approximately 40% of infected people develop symptoms, usually resembling pneumonia or influenza.
Symptoms can include:
- Cough
- Fever
- Extreme tiredness
- Shortness of breath
- Headache
- Night sweats
- Muscle aches
- Joint pain
- Skin rash
For many people, the infection eventually improves without antifungal treatment.
However, approximately 5% to 10% of infected people develop serious or long-term lung complications, and about 1% develop disseminated coccidioidomycosis, meaning the fungus spreads beyond the lungs to other areas such as the skin, bones, joints, or central nervous system.
Certain people, including those who are immunocompromised, pregnant, living with diabetes, or otherwise at increased risk, are more likely to develop serious disease.
Valley fever is unusual because it generally does not spread from one person to another. Infection usually occurs directly from the environment when fungal spores in soil become airborne and are inhaled.
Important: This article is intended for general education. Valley fever can range from mild illness to serious disseminated infection. Anyone with persistent respiratory symptoms, particularly after living in or traveling through an endemic region, should seek medical evaluation.
What Is Valley Fever?
Valley fever is the common name for coccidioidomycosis, an infection caused by fungi belonging to the genus Coccidioides.
Two major species cause human disease:
- Coccidioides immitis
- Coccidioides posadasii
Coccidioides immitis is found predominantly in California, while Coccidioides posadasii occurs primarily outside California.
No important difference in the clinical disease caused by the two species has been established.
The fungus lives naturally in soil.
When soil containing Coccidioides is disturbed, microscopic infectious structures called arthroconidia can become airborne.
People become infected when they breathe these particles into their lungs.
Valley Fever Quick Facts
| Feature | Information |
|---|---|
| Medical name | Coccidioidomycosis |
| Common name | Valley fever |
| Cause | Coccidioides fungi |
| Main species | C. immitis and C. posadasii |
| Type of organism | Fungus |
| Primary infection site | Lungs |
| Main transmission | Inhalation of airborne fungal spores |
| Person-to-person spread | Generally no |
| Typical incubation period | 1 to 3 weeks |
| Symptomatic infections | Approximately 40% |
| Serious/chronic lung complications | Approximately 5% to 10% |
| Disseminated disease | Approximately 1% |
| Common treatment | Fluconazole or other antifungal therapy when indicated |
| Severe disease treatment | May require amphotericin B |
| Vaccine available | No |
| Highly endemic U.S. regions | Southern Arizona and southern San Joaquin Valley, California |
| Prevention | Reduce exposure to contaminated dust and soil |
The History of Valley Fever
The history of Valley fever contains several major scientific surprises.
The disease was initially mistaken for a parasitic infection.
It was later discovered to be caused by a fungus.
Doctors originally believed the disease was almost always severe and frequently fatal.
Decades later, scientists discovered that most infections are actually mild or completely asymptomatic.
Research into Valley fever also helped establish the connection between environmental fungi, dust exposure, geography, and human respiratory disease.
1892: Alejandro Posadas Describes the First Recognized Case
The recorded history of coccidioidomycosis began in Argentina in 1892.
A young physician named Alejandro Posadas evaluated a soldier named Domingo Ezcurra who had developed unusual progressive skin lesions.
The lesions included wart-like and ulcerative growths.
When tissue samples were examined under a microscope, researchers saw large spherical organisms.
The structures resembled organisms known as coccidia.
Because of this resemblance, physicians initially believed the disease was caused by a protozoan parasite rather than a fungus.
Ezcurra eventually developed severe disease and died several years later.
His case became the first recognized description of what would eventually be known as coccidioidomycosis.
1890s: Similar Cases Appear in California
Not long afterward, similar cases were identified in California.
Surgeon Emmet Rixford and pathologist T. Caspar Gilchrist studied patients who developed unusual skin lesions and widespread internal disease.
One patient was a manual laborer from California’s San Joaquin Valley.
At autopsy, similar microscopic organisms were found in multiple organs.
Because these structures resembled coccidia, researchers continued to believe they were dealing with a protozoan.
In 1896, the organism was given the name:
Coccidioides immitis
The name Coccidioides reflected its apparent resemblance to coccidia.
The word immitis essentially meant “not mild,” reflecting the apparently severe nature of the early recognized cases.
1900: Coccidioides Is Recognized as a Fungus
The original protozoan theory did not last.
Around the turn of the twentieth century, William Ophüls and Herbert Moffitt demonstrated that the organism was actually a fungus.
Their experimental studies showed that Coccidioides could grow in fungal forms outside the human body and produce disease when introduced into experimental animals.
This corrected one of the major misconceptions surrounding the newly recognized disease.
Why Did Early Scientists Mistake It for a Parasite?
The mistake was understandable.
Coccidioides looks very different inside human tissue than it does in the environment.
In soil, it grows as branching fungal filaments called hyphae.
Inside the human body, however, the fungus forms large round structures called spherules.
These spherical structures can resemble certain parasites under a microscope.
The fungus therefore has dramatically different appearances depending on whether it is growing in soil or inside human tissue.
1929: A Laboratory Accident Changes Understanding of the Disease
An important moment occurred in 1929.
Medical student Harold Chope accidentally inhaled Coccidioides spores while working with a laboratory culture at Stanford University.
At the time, many physicians believed coccidioidomycosis was an exceptionally severe and usually fatal disease.
Chope subsequently developed fever and pneumonia.
The fungus was identified in his respiratory secretions.
Yet he recovered.
His survival provided an important clue that Coccidioides infection did not always produce the catastrophic disease described in early case reports.
Researchers began investigating whether mild illnesses might actually represent the same infection.
1930s: Valley Fever and Coccidioidomycosis Are Connected
Physician Ernest Dickson became one of the central figures in understanding the disease.
Doctors practicing in California’s San Joaquin Valley had long encountered patients with a relatively mild respiratory illness characterized by symptoms such as:
- Fever
- Cough
- Chest discomfort
- Fatigue
- Joint pain
- Skin rash
The illness was sometimes called:
- San Joaquin Valley fever
- Desert rheumatism
- Valley fever
By the late 1930s, researchers established that this apparently self-limited respiratory illness was caused by the same fungus responsible for severe disseminated coccidioidomycosis.
This discovery completely changed medical understanding of the infection.
Severe disseminated disease was not the usual outcome.
It represented the dangerous end of a much broader disease spectrum.
Charles E. Smith Maps Valley Fever
Another major researcher was Charles Edward Smith.
Beginning in the 1930s and continuing through subsequent decades, Smith and colleagues conducted extensive studies in California.
They investigated:
- Where infections occurred
- How frequently people became infected
- Which symptoms developed
- How immunity formed
- How skin testing could identify previous infection
- Why some patients developed severe disease
Smith’s epidemiological research helped establish that Coccidioides was closely associated with certain dry geographic regions and that many infections were mild or asymptomatic.
World War II and Valley Fever
Valley fever became an important military health concern during World War II.
Large numbers of military personnel were transferred to training facilities in the American Southwest.
Many came from regions where Coccidioides did not occur naturally.
These individuals had no previous immunity.
Training activities disturbed large amounts of dusty soil, creating ideal conditions for exposure.
Military epidemiologists documented substantial numbers of infections among service members in endemic areas.
These investigations greatly expanded scientific knowledge of:
- Environmental exposure
- Geographic risk
- Clinical symptoms
- Immunity
- Disease incidence
They also strengthened recognition of Valley fever as an important occupational and environmental infection.
1957: Amphotericin B Changes Treatment
Before effective antifungal medication became available, doctors had few treatment options for severe coccidioidomycosis.
In 1957, researchers reported successful use of amphotericin B for the treatment of coccidioidomycosis.
This represented a major therapeutic advance, particularly for patients with severe or disseminated disease.
Amphotericin B remains an important medication for serious fungal disease today.
Later development of azole antifungal drugs, particularly fluconazole and itraconazole, provided less toxic oral treatment options for many patients.
Modern Understanding of Valley Fever
Scientists now recognize Valley fever as an environmentally acquired fungal infection with a wide clinical spectrum.
Most infected people experience either:
- No symptoms
- Mild respiratory disease
- A self-limited pneumonia-like illness
A smaller group develops:
- Persistent pneumonia
- Pulmonary nodules
- Lung cavities
- Chronic pulmonary disease
- Disseminated infection
The modern challenge is often not recognizing severe disease, but recognizing Valley fever at all.
Its symptoms can closely resemble ordinary bacterial or viral pneumonia, causing delayed or incorrect diagnosis.
What Causes Valley Fever?
Valley fever is caused by exposure to fungi belonging to the genus Coccidioides.
The fungus naturally grows in certain soils, particularly in hot, dry environments.
Its environmental biology is important for understanding how infection occurs.
What Is the Life Cycle of Coccidioides?
In the environment, Coccidioides grows as a mold.
The mold consists of branching structures called hyphae.
As these structures mature, portions break apart into microscopic infectious particles known as:
arthroconidia
These particles are extremely small, approximately 2 to 4 micrometers in diameter.
When contaminated soil is disturbed, arthroconidia can become airborne.
A person can then inhale them.
Once inside the lungs, the fungus undergoes a dramatic transformation.
Instead of continuing to grow as hyphae, the arthroconidia enlarge into round structures known as:
spherules
Inside each spherule, numerous smaller structures called endospores develop.
Eventually, the spherule ruptures and releases the endospores into surrounding tissue.
Each endospore can develop into another spherule, continuing the infection.
How Do People Get Valley Fever?
The primary route is:
breathing contaminated dust or soil particles containing Coccidioides arthroconidia.
A person does not have to see a dust cloud to become infected.
Microscopic fungal particles can become airborne during ordinary environmental activity.
Exposure may occur during:
- Construction
- Excavation
- Farming
- Gardening
- Archaeological work
- Military training
- Landscaping
- Outdoor recreation
- Dust storms
- Earthquakes
- Digging
- Off-road vehicle activity
CDC specifically identifies construction, agricultural work, archaeology, and military training as activities that can increase exposure in endemic regions.
Can Dust Storms Spread Valley Fever?
Yes.
Strong winds can disturb dry soil and carry fungal particles into the air.
Dust storms can therefore increase opportunities for exposure.
However, individual infection cannot always be traced to a particular dust storm.
People living in highly endemic regions may be exposed through ordinary daily environmental conditions.
Can Earthquakes Trigger Valley Fever Outbreaks?
Large-scale soil disruption can increase airborne dust.
Earthquakes, landslides, construction projects, and other disturbances have occasionally been associated with Valley fever outbreaks.
CDC notes that outbreaks are uncommon but can follow events that disturb significant quantities of contaminated soil.
Is Valley Fever Contagious?
Under ordinary circumstances:
No.
Valley fever does not normally spread from one infected person to another.
It also does not normally spread:
- From dogs to humans
- From cats to humans
- From humans to pets
People and animals usually become infected independently after breathing fungal spores from the environment.
Are There Rare Exceptions?
Yes, but they are extremely uncommon.
CDC describes unusual transmission involving:
- Infected organ transplantation
- Contaminated objects
- Exposure associated with infected wounds
These circumstances are exceptional and do not represent the normal way Valley fever spreads.
Can Dogs Get Valley Fever?
Yes.
Dogs are particularly well known to develop coccidioidomycosis in endemic parts of the southwestern United States.
Other animals, including cats, horses, and various wild animals, can also become infected.
An infected dog does not ordinarily transmit Valley fever directly to its owner.
Both animals and humans generally acquire the fungus from environmental exposure.
Where Is Valley Fever Found?
In the United States, Coccidioides occurs primarily in the Southwest.
Historically important states include:
- Arizona
- California
- Nevada
- New Mexico
- Utah
- Texas
The fungus has also been identified in south-central Washington state.
Outside the United States, Coccidioides occurs in parts of:
- Mexico
- Central America
- South America
Where Is Valley Fever Most Common in the United States?
CDC considers Valley fever particularly endemic in:
- Southern Arizona
- California’s southern San Joaquin Valley
Arizona and California account for the large majority of reported U.S. cases.
Why Is It Called Valley Fever?
The name developed from the disease’s strong historical association with California’s San Joaquin Valley.
During the early twentieth century, physicians there began recognizing a characteristic fever and respiratory syndrome among local residents.
The illness became known as:
San Joaquin Valley fever
This was eventually shortened to:
Valley fever
The medical name remains coccidioidomycosis.
Is the Geographic Range Expanding?
Evidence suggests that scientists’ understanding of the fungus’s geographic range continues to change.
In 2013, Washington state was officially recognized as an area with locally acquired infection after investigators connected human infections to Coccidioides in local soil.
Genomic analysis showed that fungus collected from a patient’s exposure site and fungus isolated from the patient were genetically identical.
CDC also notes that changing weather and climate patterns may allow Coccidioides to survive in additional areas.
However, predicting exactly how its geographic range will change remains scientifically challenging.
How Do Weather Conditions Affect Coccidioides?
Coccidioides has an unusual relationship with rainfall and drought.
Moist conditions can support fungal growth in soil.
When conditions later become hot and dry, the soil dries out and fungal arthroconidia can more easily become airborne.
CDC notes that increases in Valley fever have been observed during hot, dry periods in Arizona and California.
This relationship helps explain why environmental and climate conditions influence disease patterns.
What Is the Incubation Period?
Symptoms usually begin approximately:
1 to 3 weeks after exposure
to airborne Coccidioides spores.
Many infected people never develop symptoms.
What Percentage of People Develop Symptoms?
Approximately 40% of infected people develop symptomatic respiratory illness.
This means roughly 60% may experience no recognizable illness.
Asymptomatic infection can still produce an immune response.
Many people only discover evidence of previous exposure through testing performed for another reason.
What Are the Symptoms of Valley Fever?
Typical symptoms include:
- Fatigue
- Cough
- Fever
- Headache
- Shortness of breath
- Night sweats
- Muscle aches
- Joint pain
- Rash
Symptoms can vary greatly between individuals.
Some patients experience a relatively mild influenza-like illness.
Others develop pneumonia severe enough to require hospitalization.
How Long Do Symptoms Last?
Many people recover within:
a few weeks to several months.
Fatigue can persist long after fever and cough improve.
More serious pulmonary or disseminated infections can continue for months or years.
What Is Desert Rheumatism?
Historically, Valley fever has sometimes been called desert rheumatism.
The term reflects a combination of symptoms that may occur during infection:
- Joint pain
- Fever
- Rash
Some people develop painful swelling of joints, particularly around the ankles or knees.
The combination of respiratory symptoms, joint discomfort, and characteristic skin findings can provide a clue to the diagnosis.
What Rash Can Valley Fever Cause?
One of the classic skin manifestations is:
erythema nodosum
This causes tender red or reddish-purple lumps, usually on the lower legs.
Erythema nodosum is an inflammatory immune reaction rather than direct fungal growth inside those particular skin lesions.
Other immune-related rashes can also occur.
Skin lesions caused by actual dissemination of the fungus represent a different and more serious situation.
What Is Primary Pulmonary Coccidioidomycosis?
When inhaled spores first cause illness in the lungs, the condition is called:
primary pulmonary coccidioidomycosis
Symptoms may resemble ordinary community-acquired pneumonia.
Possible findings include:
- Fever
- Cough
- Chest pain
- Shortness of breath
- Fatigue
- Abnormal chest X-ray findings
Most otherwise healthy people improve without serious complications.
Why Is Valley Fever Frequently Misdiagnosed?
Its symptoms are extremely similar to other respiratory infections.
A patient may initially be diagnosed with:
- Bacterial pneumonia
- Viral pneumonia
- Influenza
- Bronchitis
- COVID-like respiratory illness
Antibiotics treat bacteria but have no activity against Coccidioides.
CDC advises considering Valley fever testing in patients with pneumonia who live in or have recently traveled to endemic areas, particularly when routine treatment does not produce the expected improvement.
Can Valley Fever Cause Lung Nodules?
Yes.
Following pulmonary infection, a residual lung nodule may remain.
These nodules can sometimes be discovered incidentally on:
- Chest X-rays
- CT scans
A coccidioidal nodule can resemble lung cancer on imaging.
Clinicians may therefore need additional testing or occasionally biopsy to determine the cause.
Once an asymptomatic lung nodule is confidently established as being due to coccidioidomycosis, IDSA guidelines generally recommend observation rather than antifungal treatment in patients without significant immunosuppression.
Can Valley Fever Cause Lung Cavities?
Yes.
A cavity is an abnormal air-containing space that develops within lung tissue.
Some coccidioidal cavities cause no symptoms.
Others may cause:
- Chronic cough
- Chest pain
- Coughing up blood
- Recurrent infection
Rarely, a cavity can rupture into the space around the lung, creating a potentially serious complication.
Can Valley Fever Become Chronic?
Yes.
Approximately 5% to 10% of people who develop Valley fever experience serious or long-term pulmonary complications.
Chronic pulmonary disease may cause:
- Persistent cough
- Weight loss
- Fatigue
- Chest pain
- Breathlessness
- Lung cavities
- Progressive lung damage
Treatment can continue for many months.
What Is Disseminated Valley Fever?
Disseminated coccidioidomycosis occurs when the fungus spreads from the lungs to another part of the body.
This develops in approximately 1% of infections overall, although the risk can be substantially higher in certain vulnerable groups.
Common sites include:
- Skin
- Bones
- Joints
- Soft tissues
- Brain and spinal cord coverings
How Does Coccidioides Spread Through the Body?
After establishing infection in the lungs, fungal organisms can occasionally enter lymphatic channels or the bloodstream.
They can then travel to distant tissues.
The immune system prevents this from happening in most people.
When immune control fails, disseminated disease can develop.
What Skin Problems Can Disseminated Valley Fever Cause?
Direct fungal infection of the skin may cause:
- Papules
- Nodules
- Ulcers
- Abscesses
- Wart-like lesions
- Chronic non-healing lesions
These lesions differ from erythema nodosum because disseminated lesions may actually contain fungal organisms.
Can Valley Fever Infect Bones?
Yes.
Bone infection is one of the important forms of disseminated coccidioidomycosis.
Possible symptoms include:
- Persistent localized bone pain
- Swelling
- Reduced movement
- Spinal pain
- Neurological symptoms if the spine is involved
The vertebral column can be affected.
Severe vertebral disease can threaten spinal stability or the spinal cord and may require surgery in addition to antifungal therapy.
Can Valley Fever Affect Joints?
Yes.
Disseminated infection can involve joints.
Commonly affected locations reported in clinical guidance include:
- Knees
- Wrists
- Ankles
This represents direct infection and should not be confused with the temporary immune-related joint pains that can occur during uncomplicated Valley fever.
What Is Coccidioidal Meningitis?
One of the most serious complications is coccidioidal meningitis.
Meningitis means inflammation or infection involving the protective membranes surrounding the brain and spinal cord.
Possible symptoms include:
- Persistent headache
- Nausea
- Vomiting
- Neck stiffness
- Confusion
- Neurological abnormalities
- Changes in walking
- Vision problems
Coccidioidal meningitis is extremely serious.
Without treatment, it is fatal.
CDC states that patients who develop coccidioidal meningitis generally require lifelong antifungal treatment.
Can Valley Fever Cause Permanent Neurological Damage?
Yes.
Severe meningitis can cause complications including:
- Hydrocephalus
- Cranial nerve abnormalities
- Stroke-like complications
- Permanent neurological impairment
Rapid evaluation is important when neurological symptoms occur in a person with known or suspected coccidioidomycosis.
Who Is at Higher Risk of Severe Valley Fever?
Anyone exposed to enough airborne Coccidioides can become infected.
However, CDC identifies several groups at higher risk for severe or disseminated disease.
These include:
- People with HIV/AIDS
- Organ transplant recipients
- People receiving immunosuppressive medications
- People with diabetes
- Pregnant women
- Black people
- People of Filipino ancestry
- Older adults
Having a risk factor does not mean a person will necessarily develop severe disease.
It means closer medical assessment may be appropriate if infection occurs.
Why Does Immune Suppression Increase Risk?
Control of Coccidioides depends heavily on effective cellular immunity.
Conditions or medications that suppress immune responses can make it harder for the body to contain the fungus inside the lungs.
Important situations include:
- HIV/AIDS
- Organ transplantation
- Corticosteroid therapy
- TNF inhibitor therapy
- Other immunosuppressive treatment
Disseminated infection can become particularly severe in these populations.
Why Is Pregnancy Important in Valley Fever?
Pregnancy can increase the risk of severe or disseminated coccidioidomycosis.
The risk is particularly important during the later stages of pregnancy and the period immediately after delivery.
Changes in hormones and immune function during pregnancy are believed to contribute.
Pregnant people who live in or have traveled to endemic regions should tell their healthcare provider if they develop a pneumonia-like illness.
How Is Valley Fever Managed During Pregnancy?
Treatment during pregnancy requires specialist care because some commonly used antifungal medications can pose fetal risks.
IDSA guidance recommends considering intravenous amphotericin B for newly diagnosed nonmeningeal coccidioidomycosis requiring treatment during the first trimester.
Azole antifungals such as fluconazole may be considered later in pregnancy depending on the circumstances.
Treatment decisions depend on:
- Disease severity
- Trimester
- Previous Valley fever history
- Whether meningitis is present
- Maternal health
- Medication risks
Pregnant patients should not start or stop antifungal medication without specialist medical guidance.
Does Diabetes Increase Valley Fever Risk?
Diabetes is associated with an increased risk of more severe or complicated coccidioidomycosis.
Clinicians may therefore be more likely to consider antifungal treatment in a symptomatic patient with diabetes, particularly when pulmonary involvement is substantial.
Are Older Adults at Increased Risk?
CDC lists adults older than approximately 60 years among populations at increased risk for severe disease.
The risk may reflect a combination of aging, immune changes, and underlying health conditions.
How Is Valley Fever Diagnosed?
Diagnosis generally combines:
- Symptoms
- Travel or residence history
- Imaging
- Blood testing
- Occasionally fungal culture, microscopy, PCR, antigen testing, or biopsy
The patient’s geographic exposure history is especially important.
A healthcare provider treating pneumonia outside the Southwest may not initially consider Valley fever unless the patient mentions recent travel.
What Blood Tests Are Used?
The most common diagnostic approach is testing for antibodies against Coccidioides.
Tests can detect:
- IgM antibodies
- IgG antibodies
Methods include:
- Enzyme immunoassay, or EIA
- Immunodiffusion
- Complement fixation testing
Different tests provide different information.
What Is an EIA Test?
An enzyme immunoassay can detect antibodies against Coccidioides.
It is commonly used because it can provide relatively sensitive initial testing.
A positive result may require confirmation depending on the laboratory and clinical circumstances.
What Is Complement Fixation Testing?
Complement fixation primarily measures certain IgG antibodies.
It can help support diagnosis and can also provide information about disease activity and severity.
Doctors may repeat complement fixation titers over time to follow certain patients.
However, laboratory values must always be interpreted alongside the patient’s symptoms and clinical findings.
Can an Early Blood Test Be Negative?
Yes.
Antibodies may not yet be detectable early in the illness.
CDC’s testing algorithm advises that when clinical suspicion remains high, serology may need to be repeated approximately 2 to 6 weeks later.
Additional testing may be considered in severely ill or immunocompromised patients.
A single early negative test therefore does not always exclude Valley fever.
Can Coccidioides Be Grown in Culture?
Yes.
The fungus can be cultured from:
- Sputum
- Bronchoscopy samples
- Tissue
- Other clinical specimens
However, laboratory culture requires special safety precautions.
Coccidioides cultures can produce highly infectious airborne arthroconidia.
CDC states that culture manipulation should occur using appropriate high-level laboratory biosafety procedures.
What Does Coccidioides Look Like in Human Tissue?
Microscopy may reveal the characteristic:
spherules containing endospores.
Finding these structures in tissue can strongly support a diagnosis of coccidioidomycosis.
However, microscopy has limited sensitivity, so the absence of visible organisms does not necessarily rule out infection.
Is PCR Available?
Yes.
Molecular tests capable of detecting Coccidioides DNA have been developed.
CDC notes that an FDA-cleared PCR assay is available for detecting Coccidioides from lower respiratory specimens, although antibody testing remains the most common diagnostic approach.
Are Chest X-Rays or CT Scans Useful?
Yes.
Imaging may reveal:
- Pneumonia
- Pulmonary infiltrates
- Nodules
- Cavities
- Enlarged lymph nodes
- Chronic lung abnormalities
Imaging cannot usually confirm Valley fever by itself.
The findings need to be interpreted alongside laboratory tests and exposure history.
How Is Valley Fever Treated?
An important feature of Valley fever is that not everyone needs antifungal medication.
Many otherwise healthy people with mild primary pulmonary disease recover naturally.
CDC notes that many patients improve within a few months without antifungal treatment.
Treatment decisions depend on:
- Severity of symptoms
- Duration of illness
- Extent of lung involvement
- Immune status
- Pregnancy
- Diabetes
- Age
- Other health conditions
- Evidence of dissemination
What Treatment Is Used for Mild Valley Fever?
For mild, uncomplicated disease in an otherwise healthy person, management may include:
- Rest
- Adequate nutrition
- Fluids
- Symptom management
- Gradual return to activity
- Medical follow-up
Some people experience severe fatigue for weeks or months even after the infection begins improving.
Recovery may therefore require gradual physical reconditioning.
Which Antifungal Medicines Are Used?
Common medications include:
- Fluconazole
- Itraconazole
Other azole antifungals may be used in selected circumstances.
CDC notes that clinicians may prescribe approximately 3 to 6 months of oral antifungal therapy for patients with more serious infection or risk factors for severe disease.
The duration can be much longer for complicated infection.
When Is Fluconazole Used?
Fluconazole is commonly used for:
- Significant pulmonary disease
- Certain disseminated infections
- Coccidioidal meningitis
- Selected high-risk patients
The dose and duration vary considerably depending on disease severity and location.
Patients should not self-treat suspected Valley fever with antifungal medication.
When Is Itraconazole Used?
Itraconazole is another important azole antifungal.
It may be particularly useful for certain:
- Bone infections
- Joint infections
- Chronic infections
Medication absorption and drug interactions need to be monitored carefully.
When Is Amphotericin B Used?
Amphotericin B is generally reserved for more serious circumstances.
These may include:
- Severe rapidly progressive pulmonary disease
- Life-threatening disseminated infection
- Certain infections during pregnancy
- Patients who cannot use or do not respond adequately to azoles
Amphotericin B is highly effective but can cause significant toxicity, particularly involving the kidneys and electrolytes.
Hospital monitoring is often required.
How Long Does Valley Fever Treatment Last?
Treatment varies enormously.
A patient with moderately significant pulmonary infection may receive antifungal treatment for approximately:
3 to 6 months
Some severe infections require:
more than 6 months
Chronic or disseminated disease may require treatment lasting years.
Coccidioidal meningitis generally requires:
lifelong antifungal treatment.
Why Is Coccidioidal Meningitis Treated for Life?
Antifungal therapy can suppress the infection extremely effectively, but completely eliminating Coccidioides from the central nervous system is difficult.
Stopping medication creates a substantial risk of relapse.
For this reason, IDSA recommends lifelong azole treatment for coccidioidal meningitis.
Can Surgery Be Needed?
Yes.
Surgery is sometimes required for complications such as:
- Ruptured lung cavities
- Persistent pulmonary cavities
- Severe bone infection
- Vertebral disease
- Spinal instability
- Abscesses
- Hydrocephalus caused by meningitis
Surgery is usually combined with specialist antifungal management.
Do Antibiotics Treat Valley Fever?
No.
Antibiotics treat bacterial infections.
Valley fever is caused by a fungus.
Therefore, antibiotics such as amoxicillin, azithromycin, or doxycycline do not eliminate Coccidioides.
This is one reason correct diagnosis matters.
A patient repeatedly treated for bacterial pneumonia without improvement may actually have a fungal infection.
Can Valley Fever Go Away Without Treatment?
Yes.
Most uncomplicated infections resolve naturally.
Historical observations support this strongly.
IDSA cites early data in which the overwhelming majority of patients with uncomplicated primary pulmonary Valley fever recovered without antifungal therapy, even before effective antifungal medicines existed.
This does not mean all cases should simply be ignored.
Close medical follow-up helps ensure that complications are recognized early.
Can Valley Fever Come Back?
Most people who recover develop substantial immunity and do not experience another new infection.
CDC states that most people who get Valley fever do not get it again, and relapses are rare.
However, reactivation or relapse can occur in certain circumstances, particularly when immune function becomes severely impaired.
Can Someone Have Valley Fever for Years?
Yes.
Most infections resolve within weeks or months.
However, chronic pulmonary or disseminated disease can last for years.
Symptoms may fluctuate, and patients may require prolonged antifungal treatment and repeated medical monitoring.
Is There a Vaccine for Valley Fever?
No approved Valley fever vaccine is currently available for humans.
Researchers have been investigating potential vaccines for many years.
CDC states that scientists continue working toward a vaccine, but none is currently available.
Valley Fever Vaccine Status
| Question | Current Status |
|---|---|
| Is a human vaccine available? | No |
| Is Valley fever vaccine part of routine U.S. vaccination? | No |
| Is there an FDA-approved human Valley fever vaccine? | No |
| Are vaccines being researched? | Yes |
| Can antibiotics prevent Valley fever? | No |
| Can antifungals routinely prevent infection after dust exposure? | Not recommended for healthy asymptomatic people |
| Main prevention | Reducing inhalation of contaminated dust |
Why Is Developing a Valley Fever Vaccine Difficult?
Several challenges exist.
Researchers need a vaccine that:
- Produces strong cellular immunity
- Provides lasting protection
- Is safe in people living in endemic regions
- Does not cause disease
- Protects people at highest risk of dissemination
- Can be manufactured consistently
Fungal vaccines have historically been more difficult to develop than many bacterial or viral vaccines.
Nevertheless, Valley fever remains an active area of vaccine research.
How Can Valley Fever Be Prevented?
Preventing every exposure is difficult because Coccidioides is part of the natural environment.
A person may inhale spores without knowing that contaminated dust was present.
CDC nevertheless recommends several ways to reduce exposure.
Avoid Very Dusty Areas
When possible, avoid areas involving:
- Excavation
- Major construction
- Dust clouds
- Soil disruption
This advice is particularly relevant for people at increased risk of severe disease.
Stay Indoors During Dust Storms
During major dust events:
- Remain indoors when practical
- Close doors and windows
- Use indoor air filtration when available
These measures can reduce the amount of airborne dust inhaled.
Can an N95 Respirator Help?
CDC notes that people who cannot avoid dusty environments may consider wearing a properly fitted N95 respirator.
A loose mask may not provide the same protection.
Respirators should be used correctly according to occupational and product guidance.
Should People Avoid Gardening?
People at particularly high risk for severe Valley fever may want to reduce activities involving direct soil disturbance.
Examples include:
- Digging
- Gardening
- Landscaping
If such activities cannot be avoided, dust-reduction and respiratory precautions may help reduce exposure.
Should Soil Be Wetted Before Digging?
Moistening soil can reduce the amount of dust released during excavation.
This approach is frequently used in occupational settings in endemic areas.
It does not guarantee that exposure will be eliminated because microscopic spores may still become airborne.
Can Antifungal Medication Be Taken After Dust Exposure?
Routine antifungal medication is not recommended simply because a healthy person was exposed to dust.
CDC states there is no evidence that giving antifungals after environmental exposure prevents infection in asymptomatic workers.
People who develop symptoms should instead seek medical evaluation and testing.
Is Valley Fever a Workplace Disease?
It can be.
Higher-risk occupations in endemic areas include:
- Construction workers
- Agricultural workers
- Archaeologists
- Military personnel
- Geologists
- Utility workers
- Road crews
- Outdoor laborers
Employers in endemic regions may implement dust-control and respiratory-protection measures.
Is Valley Fever Reportable in the United States?
Reporting requirements vary by state.
CDC receives Valley fever data from states where coccidioidomycosis is reportable through the National Notifiable Diseases Surveillance System.
Surveillance helps researchers track:
- Geographic spread
- Year-to-year changes
- High-risk communities
- Outbreaks
- Long-term disease trends
How Common Is Valley Fever in the United States?
CDC states that approximately 20,000 diagnosed cases are reported each year, although the true number is believed to be much higher because Valley fever is frequently missed or never tested for.
CDC’s current national statistics page lists more than 21,000 reported U.S. cases for 2023.
Most were reported from Arizona and California.
How Many Cases May Actually Occur?
Reported cases substantially underestimate the true burden.
CDC modeling estimates approximately:
- 206,000 to 360,000 symptomatic infections per year
- 18,000 to 28,000 hospitalizations
- 700 to 1,100 deaths
The estimated number of symptomatic infections is roughly 10 to 18 times greater than reported surveillance counts.
These are modeled estimates rather than individually confirmed cases.
How Many Deaths Are Associated With Valley Fever?
CDC’s death-certificate data indicate approximately 200 coccidioidomycosis-associated deaths per year on average between 1999 and 2023.
However, burden modeling suggests the actual number of deaths associated with the disease may be substantially higher.
How Important Is Valley Fever as a Cause of Pneumonia?
In highly endemic locations, it can be a major cause.
CDC estimates that Valley fever accounts for approximately 15% to 30% of community-acquired pneumonia cases in the Phoenix and Tucson metropolitan areas.
This makes asking about geography particularly important when evaluating pneumonia in Arizona.
Why Is Valley Fever Underdiagnosed?
Several factors contribute.
Symptoms Are Nonspecific
Fever, cough, fatigue, and shortness of breath can have many causes.
Many Clinicians Practice Outside Endemic Regions
A doctor in another state may not initially consider Valley fever unless travel history is discussed.
Routine Pneumonia Testing May Not Include Coccidioides
Specific fungal testing generally needs to be ordered.
Some Infections Resolve Without Diagnosis
Patients with mild illness may never seek medical care.
Early Antibody Tests Can Be Negative
Repeat testing may sometimes be necessary.
These factors explain why surveillance numbers are much lower than estimated true infections.
Is Valley Fever Becoming More Common?
Reported U.S. Valley fever cases have increased substantially compared with the late 1990s.
For example, CDC recorded:
- 2,271 cases in 1998
- 12,926 cases in 2009
- 22,634 cases in 2011
- 20,003 cases in 2019
- More than 21,000 cases in 2023
The reasons are complex.
Possible contributors include:
- Population growth in endemic regions
- Increased construction and soil disturbance
- Changing temperature and rainfall patterns
- Improved recognition and testing
- Changes in surveillance
- Movement of people into endemic areas
CDC states that the exact reasons for year-to-year variation are not completely understood.
Can Climate Change Affect Valley Fever?
Potentially.
Coccidioides depends strongly on environmental conditions.
Changes in:
- Temperature
- Rainfall
- Drought
- Soil moisture
- Dust generation
could affect fungal growth and airborne dispersal.
CDC notes that weather and climate patterns may influence the fungus’s habitat and geographic range.
However, individual cases cannot usually be attributed directly to climate change.
Can You Get Valley Fever Anywhere in the United States?
The greatest risk remains in known endemic regions.
However, the recognized geographic range has expanded, and scientists caution that Coccidioides may exist outside historically mapped areas.
Travel history should therefore include specific locations rather than simply asking whether someone visited Arizona or California.
Is Valley Fever the Same as Histoplasmosis?
No.
Both are fungal infections acquired primarily by inhaling environmental spores, but they are caused by different fungi.
| Feature | Valley Fever | Histoplasmosis |
|---|---|---|
| Fungus | Coccidioides | Histoplasma |
| Major U.S. region | Southwest | Central and eastern U.S., especially Ohio and Mississippi River valleys |
| Main environmental source | Soil and dust | Soil enriched with bird or bat droppings |
| Main route | Inhalation | Inhalation |
| Person-to-person spread | Generally no | Generally no |
| Pulmonary disease | Yes | Yes |
| Disseminated disease | Possible | Possible |
| Vaccine | No | No |
Geographic exposure can help clinicians distinguish between fungal pneumonias.
Is Valley Fever the Same as Tuberculosis?
No.
Tuberculosis is caused by the bacterium Mycobacterium tuberculosis.
Valley fever is caused by Coccidioides fungi.
Both can produce:
- Chronic cough
- Weight loss
- Fever
- Abnormal chest imaging
- Lung cavities
However, their transmission, diagnosis, treatment, and public-health implications are completely different.
Tuberculosis can spread between people through airborne respiratory particles.
Valley fever usually comes directly from environmental fungal spores and does not ordinarily spread between humans.
Is Valley Fever a Form of Cancer?
No.
Valley fever is a fungal infection.
However, pulmonary nodules or masses caused by previous coccidioidomycosis can sometimes resemble lung cancer on imaging.
Further testing may therefore be required to distinguish the two.
Is Valley Fever an Autoimmune Disease?
No.
It is an infection caused by a fungus.
However, some symptoms, including erythema nodosum and certain joint pains, result partly from the immune response to infection.
Does a Positive Test Always Mean Active Disease?
Not necessarily.
Some antibody or skin-test results can indicate previous exposure rather than current symptomatic infection.
Diagnosis should therefore consider:
- Current symptoms
- Timing
- Imaging
- Laboratory results
- Previous infection history
A healthcare professional should interpret testing in context.
Can Someone Return to Normal Activity After Valley Fever?
Most people eventually can.
However, recovery can be slow.
Severe fatigue is one of the most persistent complaints.
Patients may benefit from gradually increasing activity rather than immediately returning to strenuous exercise.
IDSA recommends including physical reconditioning and regular medical follow-up in management of uncomplicated pulmonary coccidioidomycosis.
Can Valley Fever Be Fatal?
Yes, but fatal disease is uncommon relative to the total number of infections.
The greatest risks occur with:
- Severe diffuse pulmonary disease
- Disseminated infection
- Coccidioidal meningitis
- Major immune suppression
- Certain high-risk medical conditions
Early recognition and appropriate antifungal treatment are especially important in high-risk patients.
When Should Someone Be Tested for Valley Fever?
Testing should be considered when a person develops pneumonia-like symptoms after:
- Living in an endemic region
- Traveling through an endemic area
- Working around disturbed soil
- Exposure to significant dust
Testing becomes particularly important when pneumonia does not improve as expected with antibiotics.
When Should Someone Seek Urgent Medical Care?
Prompt or emergency medical evaluation is appropriate for symptoms such as:
- Severe difficulty breathing
- Bluish or gray skin
- Severe chest pain
- Coughing up significant amounts of blood
- Confusion
- Severe persistent headache
- Neck stiffness
- New weakness or neurological symptoms
- Seizures
- Severe spinal pain
- Rapid deterioration
People who are immunocompromised or pregnant should seek medical advice earlier if they develop compatible symptoms after possible exposure.
Frequently Asked Questions About Valley Fever
What causes Valley fever?
Valley fever is caused by Coccidioides fungi.
Is Valley fever a virus?
No.
It is a fungal infection.
Is Valley fever bacterial?
No.
Antibiotics do not treat Coccidioides.
How do you catch Valley fever?
Most people become infected by breathing microscopic fungal spores released from contaminated soil or dust.
Is Valley fever contagious?
Ordinary person-to-person transmission does not occur.
Can dogs give humans Valley fever?
Normally, no.
Dogs and humans generally become infected independently from environmental spores.
What is the incubation period?
Symptoms generally begin approximately 1 to 3 weeks after exposure.
Does everyone exposed become sick?
No.
Only about 40% of infected people develop recognizable symptoms.
What are the most common symptoms?
Common symptoms include:
- Fatigue
- Cough
- Fever
- Headache
- Shortness of breath
- Night sweats
- Muscle pain
- Joint pain
- Rash
Why does Valley fever cause extreme fatigue?
The immune response to fungal infection can be prolonged, and recovery from pulmonary inflammation can take substantial time.
Fatigue may persist after other symptoms have improved.
How long does Valley fever last?
Mild illness may improve within several weeks.
Some patients require several months to fully recover.
Chronic or disseminated cases can persist for years.
Can Valley fever heal by itself?
Yes.
Many uncomplicated infections resolve without antifungal medication.
Who needs antifungal treatment?
Treatment is more likely to be recommended for people with:
- Severe or debilitating illness
- Extensive pulmonary disease
- Immune suppression
- Disseminated infection
- Diabetes
- Pregnancy in selected circumstances
- Other significant risk factors
Treatment decisions should be individualized.
What medicine treats Valley fever?
Fluconazole is commonly used.
Other options include itraconazole and, for severe infection, amphotericin B.
Can amoxicillin treat Valley fever?
No.
Amoxicillin is an antibacterial medication.
It does not kill Coccidioides fungi.
Can Valley fever spread to the brain?
Yes.
Rarely, disseminated infection causes coccidioidal meningitis.
Can Valley fever spread to bones?
Yes.
Bones and joints are among the more important sites of disseminated coccidioidomycosis.
How common is disseminated Valley fever?
CDC estimates dissemination occurs in approximately 1% of infections overall.
Can Valley fever cause lung cavities?
Yes.
Pulmonary cavities can occur following infection.
Some remain asymptomatic, while others produce chronic symptoms or complications.
Can Valley fever leave lung nodules?
Yes.
Residual nodules may remain after infection and can sometimes resemble malignancy on chest imaging.
Can you get Valley fever twice?
Most people develop substantial immunity after infection, and reinfection is considered uncommon. CDC states that most people do not get Valley fever again.
Is there a Valley fever vaccine?
No approved human vaccine is currently available.
Research is ongoing.
Does wearing a mask prevent Valley fever?
A properly fitted N95 respirator may reduce exposure when dusty conditions cannot be avoided, but no protective measure completely eliminates environmental exposure in endemic regions.
Can Valley fever be prevented with antifungal medication after dust exposure?
Routine post-exposure antifungal medication is not recommended for healthy asymptomatic people because evidence does not show that it prevents infection.
Is Valley fever common in Arizona?
Yes.
Arizona is one of the two states reporting the largest numbers of U.S. cases.
Is Valley fever common in California?
Yes.
It is particularly associated with California’s southern San Joaquin Valley and other endemic areas of the state.
Is Valley fever found in Washington?
Yes.
Locally acquired infections have been confirmed in parts of south-central Washington.
Can pregnant women get severe Valley fever?
Yes.
Pregnancy, particularly later pregnancy and the immediate postpartum period, is associated with increased risk of severe or disseminated disease.
Can children get Valley fever?
Yes.
Anyone who inhales infectious spores can become infected.
Can Valley fever cause death?
Yes.
Most infections are mild or asymptomatic, but severe pulmonary, disseminated, or central nervous system disease can be fatal.
Why Valley Fever Remains an Important Disease
Valley fever occupies an unusual position in infectious disease history.
The first recognized patient was identified in Argentina in 1892.
Doctors initially thought the strange spherical structures visible in his skin represented a protozoan parasite.
Similar cases soon appeared in California.
By the beginning of the twentieth century, scientists had demonstrated that the organism was actually a fungus.
Yet another misunderstanding remained.
Because the earliest diagnosed patients had severe disseminated disease, physicians assumed coccidioidomycosis was usually devastating.
A laboratory accident in 1929 helped challenge that assumption when a medical student inhaled Coccidioides, developed pneumonia, and survived.
Research during the 1930s then demonstrated that the common illness known as San Joaquin Valley fever was caused by the same fungus responsible for severe disseminated coccidioidomycosis.
Scientists subsequently discovered that most infections are actually asymptomatic or relatively mild.
Today the problem has changed.
Valley fever is no longer considered an obscure, inevitably fatal fungal infection.
Instead, it is recognized as an important cause of community-acquired pneumonia in the American Southwest.
CDC estimates that approximately 20,000 diagnosed cases are reported annually, while disease-burden modeling suggests that more than 200,000 symptomatic infections may actually occur in a typical year.
The fungus is also being identified outside some historically recognized endemic regions.
Environmental changes, migration, construction, dust exposure, improved diagnostic testing, and greater clinical awareness are all influencing how the disease is understood.
The biggest challenge is often simply considering the diagnosis.
A patient may develop fever, cough, fatigue, and pneumonia after visiting Arizona or California and receive repeated antibiotics because the illness appears bacterial.
Without asking about travel history and testing for Coccidioides, the true diagnosis may remain hidden.
For most people, Valley fever eventually resolves.
For a smaller group, however, the infection can damage the lungs for years or escape into the bones, joints, skin, or central nervous system.
Coccidioidal meningitis can be fatal without treatment and generally requires lifelong antifungal therapy.
There is currently no approved human vaccine.
Prevention therefore depends on recognizing geographic risk, reducing unnecessary exposure to airborne dust, protecting high-risk workers and patients, and diagnosing disease early when symptoms develop.
More than 130 years after the first recognized case, Valley fever remains an important example of how a microorganism living quietly in soil can become a significant human disease when environmental conditions, geography, and human activity bring fungus and host together.
Medical information reviewed against CDC, Infectious Diseases Society of America guidance, NIH/PubMed literature, and current U.S. public health information available through September 2026.