Common invasive fungal diseases: an overview of invasive candidiasis, aspergillosis, cryptococcosis, and Pneumocystis pneumonia

Every year, Candida, Aspergillus, Cryptococcus and Pneumocystis infect an estimated two million individuals worldwide. Most are immunocompromised or critically ill. Candida is the most common fungal pathogen of the critically ill and of recipients of transplanted abdominal organs. In high-risk haemato-oncological patients, in contrast, the introduction of antifungal prophylaxis with fluconazole and later with mould-active posaconazole has led to a remarkable reduction of invasive candidiasis and is likely to have a similar effect on invasive aspergillosis. Invasive aspergillosis remains the dominant invasive fungal disease (IFD) of haemato-oncological patients and solid-organ transplant recipients and is increasingly found in individuals with exacerbated chronic obstructive pulmonary disease on corticosteroids. In the developed world, owing to antiretroviral therapy Pneumocystis pneumonia and cryptococcosis have become rare in patients with human immunodeficiency virus (HIV) and are mainly found in solid-organ transplant recipients or immunocompromised patients. In the developing world, cryptococcosis remains a common and highly lethal disease of HIV positive individuals. With invasive candidiasis and invasive aspergillosis, timely diagnosis is the principal challenge. The clinical presentation is nonspecific and current diagnostic tests lack sensitivity and specificity. The combination of several tests improves sensitivity, but not specificity. Standardised polymerase chain-reaction-based assays may be promising tools for more rapid and specific diagnosis of candidiasis and invasive aspergillosis. Nevertheless, initiation of treatment is often based solely on clinical suspicion. Empirical therapy, however, may lead to over-treatment of patients without IFD or it may miss its target in the case of resistance. Despite the success of antifungal prophylaxis in reducing the incidence of IFDs in haemato-oncological patients, there are a considerable number of breakthrough infections demonstrating not only fungal resistance but also the emergence of rare and often lethal fungal pathogens. Knowledge of the local epidemiology and antifungal resistance is therefore pivotal. Current trial-based guidelines leave major gaps in identifying those most at risk, who may benefit from prophylaxis. Ongoing searches for disease-associated genetic polymorphisms may contribute to the establishment of individual risk profiles and targeted prophylaxis.