Metagenomic next-generation sequencing reveals cross-reactivity of lateral flow cryptococcal antigen assay with Trichosporon inkin.

Metagenomic next-generation sequencing (mNGS) in plasma, cerebrospinal fluid (CSF), and bronchoalveolar lavage fluid is a relatively new technology that offers a means to potentially provide a diagnosis in cases where infection is suspected, but conventional diagnostic testing has not revealed a pathogen. There have been many publications of individual cases and overall appraisals of its utility in detecting bacteria, fungi, and DNA viruses associated with otherwise undiagnosed systemic infections. A recent article by Phillips et al. published in ASM Case Reports (2:e00053-25, 2025, https://doi.org/10.1128/asmcr.00053-25) presents a case of meningitis in an immunosuppressed child that was ultimately determined to be caused by Trichosporon inkin using mNGS. Elevated ß-1,3-D-glucan (BDG) levels in CSF and serum projected a diagnosis of fungal meningitis. Bacterial, fungal, and mycobacterial cultures were negative. Positive lateral flow cryptococcal antigen titers in serum and CSF complicated the anticipated diagnosis since Cryptococcus spp. are thought to not have sufficient cell wall BDG to produce positive test results. Given the ultimate diagnosis of T. inkin meningitis and the known cross-reactivity with Trichosporon asahii per package insert, the unexpected cryptococcal antigen results raised the possibility of additional cross-reactivity. The authors uncovered this possibility by testing three known clinical isolates of T. inkin which generated positive results. This case adds to the growing literature that highlights the utility of mNGS in providing a diagnosis in otherwise unresolved cases and shows that mNGS can be further instructive in elucidating limitations in commonly used diagnostic tests.