Detection of Pulmonary Toxoplasma gondii Causing Atypical Pneumonia in an Immunosuppressed Patient through Metagenomic Sequencing

Background Pulmonary toxoplasmosis is a rare but critical opportunistic infection in immunosuppressed individuals, often presenting as atypical pneumonia. Conventional diagnostic methods, including serology and cultures, may yield false negatives, complicating timely diagnosis and treatment. Methods: A bronchoalveolar lavage sample was obtained from a 48-year-old immunosuppressed patient hospitalized with atypical pneumonia. The sample underwent next-generation sequencing (NGS)-based metagenomic analysis, including nucleic acid extraction, library preparation, high-throughput sequencing, and bioinformatic pipeline processing for microbial identification. Results: NGS identified Toxoplasma gondii DNA in the bronchoalveolar lavage sample, confirming a diagnosis of pulmonary toxoplasmosis. Remarkably, the patient responded clinically to metronidazole monotherapy, achieving significant symptom resolution. Follow-up computed tomography revealed complete radiological improvement, confirming clinical cure. Discussion: This case underscores the value of metagenomic sequencing in diagnosing atypical pathogens where conventional approaches fail. The identification of Toxoplasma gondii highlights the expanded utility of NGS in pulmonary infections, particularly in immunosuppressed patients. The unexpected success of metronidazole as a sole treatment raises questions about its potential efficacy against Toxoplasma gondii, warranting further investigation. Conclusion: Metagenomic diagnostics represent a powerful tool in identifying rare infectious agents and guiding effective interventions. This case highlights the clinical significance of NGS in improving diagnostic precision and broadening therapeutic horizons for pulmonary toxoplasmosis.