Geotrichosis fungal infection. Light micrograph of a tissue sample from a patient with geotrichosis, a disease caused by infection with the fungus Geotrichum candidum. The fungus is seen as the long black threads amongst the cells (blue and pink). Geotrichum infection usually occurs in patients with suppressed immune systems, such as those with AIDS or those on immunosuppressant drugs. The infection is usually based in the lungs, where it causes a cough, bloody sputum and mouth lesions similar to those found in thrush. Antifungal drugs can clear up the condition.