Is valley fever contagious?

Valley Fever Is Not Contagious

Valley fever (coccidioidomycosis) is not contagious and cannot spread from person to person. The disease is acquired exclusively through inhalation of fungal spores from soil or dust in endemic areas 1, 2.

Mode of Transmission

Valley fever is caused by the fungi Coccidioides immitis or Coccidioides posadasii, which live in the soil in specific geographic regions. The transmission process occurs as follows:

• The infection is acquired by inhaling airborne fungal spores from the environment 2
• No person-to-person transmission occurs 2
• No zoonotic transmission (animal to human) occurs 2

This contrasts with many other infectious diseases that can spread through:

• Direct contact between people
• Respiratory droplets
• Contaminated surfaces
• Vector-borne transmission

Geographic Distribution

Valley fever is geographically restricted to:

• Southwestern United States (primarily Arizona and California) 2, 3
• Parts of Mexico
• Central and South America

In California alone, valley fever incidence increased 213% from 2014 to 2018 3, highlighting its significance as a regional health concern.

Risk Factors

Since valley fever cannot spread between people, risk is associated with:

1. Environmental exposure: Living in or traveling to endemic regions 1
2. Activities that disturb soil: Construction, farming, archaeology, or outdoor recreation in endemic areas 4
3. Weather conditions: Periods following rain followed by dry conditions that promote fungal growth and spore dispersal (the "grow and blow" hypothesis) 4

Clinical Presentation

Valley fever presents similarly to other community-acquired pneumonias, which can lead to misdiagnosis:

• It accounts for 17-29% of community-acquired pneumonia cases in some endemic regions 2, 5
• Common symptoms include fever, cough, fatigue, chest pain, headache, and rash 1
• The disease can present as an acute respiratory infection, chronic pneumonia, or disseminated disease 1

Diagnostic Considerations

When evaluating patients with pneumonia-like symptoms:

• Always obtain a travel history to endemic areas 2
• Consider serologic testing (enzyme immunoassay with immunodiffusion confirmation) 2
• Be aware that serologic tests may not be positive until 1-3 weeks after disease onset 2

Prevention

Since valley fever is not contagious, prevention focuses on environmental exposure:

• Avoid activities that generate dust in endemic areas
• Use dust masks during unavoidable dust exposure
• Be aware of your risk if living in or traveling to endemic regions 3

Common Misconceptions

A significant knowledge gap exists regarding valley fever:

• Only 42.4% of Californians reported general awareness of valley fever 3
• Only 25% of people living in high-incidence regions were aware they lived in areas where the fungus exists 3
• Among those with risk factors for severe disease, only 3.5% knew they were at increased risk 3

Unlike diseases such as Q fever, which can occasionally spread through person-to-person contact 1, or yellow fever, which is transmitted by mosquitoes 1, valley fever is strictly acquired through environmental exposure to fungal spores.