Because H. capsulatum can be found in dirt and soil—particularly in central parts of the United States—it is very difficult to prevent coming into contact with the fungus. Moreover, H. capsulatum can live in a person's body for many months or possibly years before it causes disease, depending on the health of the person's immune system.
If your T-cell count is below 150, you should take care when engaging in certain activities—or avoid them altogether—if you live in central parts of the United States or other parts of the world where H. capsulatum is prevalent. For example, it's a good idea to wear a mouth and nose guard/mask if dust is created while working with surface soil, or cleaning chicken coops, disturbing soil beneath bird-roosting sites, or exploring caves.
Because histoplasmosis is more likely to occur in HIV-positive people with compromised immune systems, a good way to help prevent it from occurring is to keep the immune system healthy, such as by using antiretroviral drugs, reducing stress, eating right, and getting plenty of rest. Sporanox, at a dose of 200 mg a day, is a possible preventive treatment for HIV-positive people with fewer than 150 CD4 cells who are at high risk for H. capsulatum infection because of their work or residence in a high-prevalence area—Sporanox can be discontinued when the person's CD4 count remains above 150 for at least six months.