Cocci is a fungus present in certain areas of the Western Hemisphere. You can get infected with Cocci if you live or travel to these areas. Read on to learn more about this infection or the fungus that causes it.



Coccidioidomycosis, (pronounced  kok-SID-ee-oy-doh-my-KOH-sis), commonly called Valley Fever or Cocci, is a fungal disease caused by the Coccidioides (pronounced kok-SID-ee-oy-deez) fungus. The Cocci fungus is endemic in the Southwest United States and the arid areas of Eastern Washington State, as shown in Figure 1. Outside of the United States, this fungus is present in parts of Mexico and South and Central America. The areas where Cocci can be found seem to be expanding, potentially due to changes in rainfall and temperature associated with climate change. Periods of drought can also increase the number of Cocci infections in the endemic region.

Figure 1. Areas where Coccidioides fungi can be found. Reproduced with permission from CDC and MSGERC.

Cocci is a growing problem. In 2019, there were 20,003 confirmed cases of Valley Fever reported in the United States. Most cases are diagnosed in people living in or visiting Arizona or California. The number of cases is believed to be drastically underestimated because many people affected by the disease aren’t diagnosed. Most people who experience Cocci will recover, but unlike symptoms associated with more common respiratory illnesses, the symptoms associated with Cocci may last six months or longer. On average, approximately 200 deaths a year are attributed to Cocci in the United States. This is also likely underreported. The economic impact of the disease is estimated to be more than 1.5 billion US dollars. For these reasons, improving awareness, diagnosis, and the management of Cocci will have a large public health impact.

Key Term:

Endemic means regularly occurring within an area or community.

What’s in a Name?

You may hear Cocci referred to in several ways. For simplicity, on first mention we will use the technical term, then through the rest of the document we will use the short term, Cocci. Here are some of the other terms you may encounter that describe the disease or the fungus, along with a brief explanation of how  those terms arose:

  • “Valley Fever”—this is the term typically used to describe the fungal lung infection caused by Cocci. Sometimes it’s used to describe other forms of the disease. It gets its name because the first cases described in the United States occurred in in the San Joaquin Valley of California
  • “San Joaquin Valley Fever”—another term that shows a geographical association
  • “Desert rheumatism”—this name came about because Cocci is often present in the desert region. Rheumatism is added to “desert” because people can develop painful joints from the fungus because of their body’s reaction to the fungus (inflammation)
  • “Cocci”—this term is just a lot shorter and easier to say than Coccidioides or coccidioidomycosis
  • “Disseminated cocci” or “Disseminated Valley Fever”—this term means that the disease has spread from the primary location (usually the lung) to other parts of the body
  • “Cocci Meningitis,” “Valley Fever Meningitis,” or “CNS Cocci” – these terms refer to disease that has invaded the brain or central nervous system

Science Sidebar:

Why is coccidioidomycosis such a long, difficult name? There is a reason. The people who first described Cocci saw a large structure in the tissue and thought it could be a protozoan parasite similar to Coccidia. That’s where the confusion arose and how the term Coccidioides (resembling Coccidia) arose. Later on, researchers realized that they were looking at the spherule phase of a fungal organism (more on that in the other Science Sidebar). In your reading, you may come across the term coccidiosis, which is the gastrointestinal illness caused by Coccidia. It typically occurs in livestock. Don’t get confused—these are different diseases. People with Valley Fever can still raise or be around chickens or other livestock.

Key Term:

Protozoan is a single-cell animal of the family Protista, which includes the amoeba.

How Do You Get Infected?

From airborne spores

Coccidioides fungi live in the soil in what is called the mycelial phase (see SCIENCE SIDEBAR for detail) in environments that are dry (arid or semiarid). As shown in Figure 2, when the soil is disturbed—by human activities like excavation, animal activities, or weather events like earthquakes or fires—fungal arthrospores (we’ll call them spores for simplicity) are released into the air. These spores are not visible to the naked eye, and once in the air can travel 75 miles or more from where they became airborne. People (and animals) can inhale these spores. Once inside the body, the fungus changes to a different form and grows into spherules, which eventually release new fungal cells (endospores) and the process continues. This is the lifecycle of the fungus and the typical method of disease transmission.

Figure 2. Lifecycle of Cocci, showing the phases in the soil and in the mammalian host. Reproduced with permission from the CDPH Valley Fever Fact Sheet.

Through your skin

Less commonly, fungal spores can enter your skin through a cut, wound, or splinter and cause a skin infection. This is known as an implantation mycoses. This method of transmission is rare but has been documented in fieldworkers or people with traumatic injuries.

Frequently Asked Questions

Cocci is not spread from person to person.. The normal route of infection is from inhalation; however, there have been some rare cases where infection was caused by:

  • A wound infected with Cocci releases spores in the air, which people inhale
  • Organ transplant from an infected donor
  • Contact with a contaminated item, such as an article of clothing
  • Exposure of laboratory personnel to Cocci while processing a specimen

Pregnant women don’t seem to be able to transmit the Cocci infection to their babies.

Key Terms:

Genus is a category of an organism that is “above” a species and “below” a family in the organism taxonomic (organizational) system.
Mycelium is a root-like fungal structure with branching, thread-like filaments called hyphae.
Arthrospores are yeast-like individual fungal cells formed by the breaking down of hyphae.

Figure 3: Forms of Cocci during the different lifecycle stages. Modified from image provided by Saurabh Patil, via Wikimedia Commons.

Science Sidebar:

Coccidioides – the Shape Shifter

Coccidioides is a fungal genus. A genus is usually italicized and written with an initial capital letter. It is often written in connection with a specific species, which is written in lowercase and is also italicized. Sometimes the genus is abbreviated to a 1 letter (eg, C. for Coccidioides). Can you recognize this genus/species: Homo sapiens (or H. sapiens)? The species of Coccidioides that cause disease are Coccidioides immitis and Coccidioides posadasii.

Coccidioides is described as a dimorphic fungus, which means it exists in two distinct forms as shown in Figure 3. It can exist as a mycelium (mold) containing hyphae, typically in the soil. When the soil dries out, hyphae develop into arthrospores. These arthrospores (spores) are small enough to become airborne and can cause disease if inhaled. Once a spore enters the lung, it  undergoes a change to become a spherule, which is a big, sturdy sack-like structure. Inside the spherule, the fungal cells multiply, become endospores, and fill up the sack. When the spherules rupture in a few weeks, the endospores are released and spread out (disseminate). They can then form new spherules, and the cycle continues.