How to use direct microscopy for diagnosing fungal infections

Abstract

Background: Invasive fungal infections are an important cause of morbidity and mortality in a broad range of patients. Adequate and early diagnosis is a challenge and of importance for improved survival. New molecular-based diagnostic methods are trendsetting, yet with the drawback that conventional tests receive less attention, in the laboratory as well as in the clinical setting.

Objectives: We aimed to provide a useful recommendation for direct microscopy for effectively managing numerous specimens related to fungal infections, mainly covering opportunistic pathogens.

Sources: A PubMed literature search covering direct fungal microscopy was performed with no restrictions on publication dates.

Content: Best practise recommendations targeting the role of direct microscopy in diagnosing fungal infections are given. This review highlights when to perform direct microscopy, displays the main fungal morphologies, discusses the pitfalls related to microscopy, and recommends how to best report the results to clinicians.

Implication: In many samples, the performance of direct microscopy provides an important diagnostic benefit that is greater than culture alone. Fluorescent dyes improve sensitivity and allow a fast and rapid read. Reporting includes the presence or absence of yeast forms, septate or non-septate hyphae, pigmentation, cellular location, or any other specific structures being present. The visualization of fungal elements from a sterile body site is proof of an infection, independent of other test reports.

Keywords: Direct microscopy; Early diagnosis; Fungal infections; Fungal morphology; Hyphae and pseudohyphae; Proof of infection.