Pulmonary Nocardiosis Diagnosed by Plasma Metagenomic Next-Generation Sequencing in a Patient With Recurrent Febrile Neutropenia.

BackgroundNocardiosis disproportionately affects immunocompromised hosts. Early identification of Nocardia infections is critical as delays can lead to worse outcomes. Species such as N. farcinica are associated with increased risk of dissemination and resistance. Diagnosis of opportunistic infections in immunocompromised populations relies on culture, antigen, or serologic methods that often have limited sensitivity or specificity. Plasma microbial cell-free DNA metagenomic next-generation sequencing (mNGS) offers a noninvasive approach for early diagnosis of opportunistic infections.Case presentationWe report a case of pulmonary nocardiosis in an 87-year-old man with myelodysplastic syndrome and prolonged neutropenia diagnosed by plasma mNGS. He had been hospitalized multiple times with recurrent febrile neutropenia and respiratory symptoms. Standard noninvasive microbiologic workup was unrevealing, but lower respiratory specimens could not be readily obtained. Due to elevated risk of complications from invasive testing, plasma mNGS was used as a complementary tool and identified N. farcinica. Anti-Nocardia therapy was initiated, and his fevers resolved.ConclusionmNGS is an emerging diagnostic tool that may identify Nocardia species from clinical specimens with a faster turnaround time than culture and enables rapid species identification. Although culture is still recommended for susceptibility testing, mNGS may expedite diagnosis in particular situations. This case supports the role of plasma mNGS as a complementary tool in the evaluation of febrile neutropenia and highlights its diagnostic potential.