Non-cultural methods for the diagnosis of invasive fungal disease

Abstract

Invasive fungal diseases carry a high mortality risk which can be reduced by early treatment. Diagnosing invasive fungal diseases is challenging, because invasive methods for obtaining histological samples are frequently not feasible in thrombocytopenic immunocompromised patients, while fungal cultures have low sensitivity and a long turn-around time. Non-cultural methods are fundamental for a rapid diagnosis of invasive fungal diseases and they include assays based on the detection of fungal antigens (galactomannan, Aspergillus-lateral flow device, [1,3]-β-D-glucan, mannan), antibodies, such as anti-mannan, and molecular tests. With the exception of some molecular methods for rare fungi, the non-cultural assays are usually applied to the diagnosis of invasive aspergillosis, invasive candidiasis and pneumocystosis. The performance of a single test or a combination of tests will be discussed, with particular focus on choosing the most appropriate marker(s) for every specific patient population. Reasons for potential false-positive or false-negative results will be discussed.

Keywords:

• (1,3)-β-D-glucan
• Aspergillus lateral flow device
• fungal PCR
• galactomannan
• invasive aspergillosis
• invasive candidiasis
• mannan
• pneumocystosis

Financial & competing interests disclosure

M Mikulska has been a member of advisory board for Pfizer, Merck, Astellas and Gilead. C Viscoli has acted as consultant and member of advisory board for Pfizer, Merck, Astellas and Gilead. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Key issues

• Non-cultural methods include testing for fungal antigens, DNA or antibodies in clinical samples and the most important assays are cryptococcal antigen in serum and cerebrospinal fluid, galactomannan (GM) in serum, bronchoalveolar lavage fluid and cerebrospinal fluid, serum (1,3)-β-D-glucan (BG) and molecular tests.

• Serum GM has high sensitivity and sensibility for diagnosis of invasive aspergillosis (IA) in neutropenic patients, while in non-neutropenic populations GM in broncoalveolar fluid should be used.

• New point-of-care lateral flow device for the diagnosis of IA (Aspergillus-LFD) has been marketed and its performance is similar to that of GM.

• (1,3)-β-D-glucan is present in all invasive fungal disease, with exception of mucormycosis and most cases of cryptococcosis, and it has good performance for diagnosing invasive candidiasis, less compelling data for IA and an excellent performance for pneumocystosis.

• Although numerous causes of false-positive BG results have been reported, two consecutive positive results had very high specificity in hematology patients.

• Molecule methods hold much promise although technical difficulties are not irrelevant, the dynamic of serum release of fungal DNA during an invasive fungal disease is largely unknown and most of the data come from in-house non-validated assays.

• Culture for fungi of relevant clinical samples (e.g., in case of IA) should always be pursued in the era of an increasing risk of infection due to resistant fungi, until molecular methods for resistance testing in culture-negative samples are proved reliable and widely available.