Histoplasmosis is an infection caused by a fungus called Histoplasma. The fungus lives in the environment, particularly in soil that contains large amounts of bird or bat droppings. In the United States, Histoplasma mainly lives in the central and eastern states, especially areas around the Ohio and Mississippi River valleys. The fungus also lives in parts of Central and South America, Africa, Asia, and Australia.
People can get histoplasmosis after breathing in the microscopic fungal spores from the air. Although most people who breathe in the spores don’t get sick, those who do may have a fever, cough, and fatigue. Many people who get histoplasmosis will get better on their own without medication, but in some people, such as those who have weakened immune systems, the infection can become severe.
In the United States, an estimated 60% to 90% of people who live in areas surrounding the Ohio and Mississippi River valleys (where Histoplasma is common in the environment) have been exposed to the fungus at some point during their lifetime. One study calculated the incidence of histoplasmosis in adults aged 65 years and older in the U.S. to be 3.4 cases per 100,000 population. Rates were highest in the Midwest, with an estimated 6.1 cases per 100,000 population.
Most people who are exposed to the fungus Histoplasma never have symptoms. Other people may have flu-like symptoms that usually go away on their own.
Symptoms of histoplasmosis include: