Aspergillus is a fungus found in soil, on farms and on construction sites. In those whose immune system is impaired it causes severe infection. The people who are particularly at high-risk of infection with Aspergillus (which is called Invasive Aspergillosis)are those with acute leukaemia who are having chemotherapy and those post bone marrow transplantation. Currently 15% of those at high-risk develop Invasive Aspergillosis and 60-90% of those with Invasive Aspergillosis die.