Infantile pulmonary abscess due to Mycobacterium abscessus subsp. massiliense identified by integrated mNGS and targeted NGS: a rare case report.

BACKGROUND

To describe a rare case of pulmonary infection caused by Mycobacterium abscessus in an infant and to evaluate the complementary diagnostic value of metagenomic next-generation sequencing (mNGS) and targeted next-generation sequencing (tNGS) in identifying non-tuberculous mycobacterial (NTM) infections when conventional testing is inconclusive.

CASE PRESENTATION: A 3-month-old male infant presented with a persistent cough and a right upper-lobe mass, initially suspected to be a congenital malformation or neoplasm. Following inconclusive routine examinations, mNGS was performed on bronchoalveolar lavage fluid (BALF). mNGS detected a single read of M. abscessus in BALF, providing an initial diagnostic clue. Subsequently, a tNGS assay was conducted on both BALF and resected lung tissue to achieve precise species identification. tNGS identified 13,272 reads of M. abscessus subsp. massiliense in BALF and 31,474 reads in lung tissue, confirming the pathogen and enabling precise molecular diagnosis. Histopathological examination revealed granulomatous inflammation with multinucleated giant cells, consistent with NTM infection. Guided by these results, the patient initially received azithromycin and was transferred to a specialized chest hospital, where a multidrug anti-NTM regimen was formulated, including azithromycin, imipenem-cilastatin, cefoxitin, and linezolid. After continued treatment at a local municipal hospital, respiratory symptoms resolved, inflammatory markers improved, follow-up CT showed progressive absorption of the right upper-lobe lesion with a small residual cavity, and the patient was discharged in stable condition without recurrent infections during available follow-up.

CONCLUSION

This case highlights the diagnostic utility of integrating mNGS and tNGS for the accurate identification of rare NTM infections in infants, particularly when routine microbiological tests and imaging findings are inconclusive.