Cryptococcal meningitis is hard to treat, so it is very serious. Diagnosis is with a negative stain looking for the capsule in CSF of suspected cases. This fungal microbe used to be called a protozoan. Pneumocystis infection were rare until AIDs. Pneumocystis is the most common fatal infection in AIDs patients and in chemotheraphy patients.
Fungal infections are hard to treat and the microbes are ubiquitous in the environment.
This is a bad combination for the immunocompromised. The mold has no yeast phase, but the mold form produces a metabolic product called Aflatoxin . Aflatoxin is a very potent poison and carcinogen that gets into grain in dry seasons. There was a cereal scare in the late 1980s. The FDA monitors the amount of toxin in grain products since it is always there in low levels.