What are the definitions of invasive fungal disease?

Here, we will take a closer look at the three consensus definitions of Invasive Fungal Disease (IFD). The first consensus definitions were published in 2002 by Ascioglu et al in an attempt to standardise the definitions and provide a classification based on the level of certainty for the diagnosis of IFD to be used in epidemiological studies and clinical research.

Revised consensus definitions were then published in 2008 and 2019, due to advances made in fungal diagnostic tools, as well as the acknowledgement that the definitions were unsuitable for special patient populations, including those in ICU settings and paediatric patients (de Pauw et al, 2008; Donnelly et al, 2019).

The definitions assign three levels of probability to the diagnosis of IFD namely, ‘proven’, ‘probable’, and ‘possible’.

Proven IFD

This requires the detection of the fungus in a tissue sample or culture of a specimen obtained from a normally sterile site. In the case of cryptococcosis, detection of cryptococcal antigen in blood or CSF is also sufficient to prove the diagnosis. For pneumocystosis (PCP), detection of Pneumocystis in BAL fluid or expectorated sputum using conventional or immunofluorescence staining is considered to prove a diagnosis of PCP.

The underlying principle of the classification of probable and possible IFD is to combine host factors identifying the patient at risk, clinical signs and symptoms consistent with the disease phenotype, and mycological test results. Host factors, clinical features and mycological evidence are further specified by the following categories of IFD: invasive pulmonary mould diseases, candidiasis, cryptococcosis, pneumocystosis, and endemic mycoses (Donnelly et al, 2019).

Probable IFD

Thisrequires the presence of one host factor, one clinical feature and one mycological criterion.

Possible IFD

This requires the present of a host factor and a clinical feature, but this should not be applied to endemic mycosis because host factors and clinical signs and symptoms not being sufficiently specific.

The EORTC/MSG Consensus Definitions have proven their value and have been used in major clinical trials including antifungal efficacy studies, comparison of management strategies, evaluation and validation of diagnostic tests and epidemiological studies.