Cryptic aspergillosis: a rare entity and a diagnostic challenge.

Introduction: Cryptic aspergillosis, caused by cryptic species of , is increasingly reported in humans and causes significant morbidity and mortality in immunocompromised individuals. The main aim of this study was to describe the occurrence of this entity at a large tertiary care centre and analyse the challenges in identifying them in a routine diagnostic laboratory.

Methods: This was a retrospective case review of all patients diagnosed with cryptic species from April 2019 to February 2020. The isolates were identified using conventional microbiological techniques, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI- TOF MS), 28S rRNA and internal transcribed spacer (ITS) sequencing.

Results: The species identified were and . Identification by MALDI- TOF MS and sequencing was concordant for all except , with MALDI- TOF MS misidentifying it as . All isolates showed low minimum inhibitory concentrations (MICs) for the panel of antifungal drugs.

Conclusion: Aspergillosis caused by cryptic species presents a diagnostic challenge. This study confirms the importance of molecular methods for accurate identification.