Metagenomic next-generation sequencing (mNGS) is widely used as a more promising technology than conventional tests. However, its clinical utility in the context of bronchoalveolar lavage fluid (BALF) samples for discriminating between non-severe and severe pneumonia is not well established. Thus, this study aimed to investigate the diagnostic performance of mNGS on BALF samples from 100 individuals suspected of pneumonia, and compared it with conventional microbiological tests (CMT) of BALF samples and the final clinical diagnosis. Twenty-seven cases of non-severe pneumonia and 73 cases of severe pneumonia patients were finally clinically diagnosed. Among 100 cases, diagnostic performance of mNGS and culture showed a significant difference; 65 cases had the same sample types, of which 25 cases were diagnosed as positive by mNGS only (38.46%) and 1 was diagnosed as positive by culture only (1.54%). Moreover, 24 cases were diagnosed positive in both mNGS and culture (36.92%) and 15 cases tested negative in both mNGS and culture (23.08%). Among 35 cases, 28 out of 35 cases were diagnosed as positive by mNGS, while only 4 out of 35 cases were diagnosed as positive by the indirect immunofluorescence method (IIFT). In addition, the positive rate of mNGS was higher than that of culture in cases regardless of prior antibiotic exposure. Mixed pathogens were found to be significantly more prevalent in severe pneumonia patients than in non-severe pneumonia patients. Importantly, among 38 cases who were diagnosed solely by mNGS, 25 patients experienced an improved outcome after physicians changed the therapy according to the mNGS results. In conclusion, the results showed that mNGS of BALF represents a potentially effective tool for detection of mixed pathogens in severe pneumonia.

宏基因组下一代测序（mNGS）作为比传统测试更有前景的技术而被广泛使用。然而，其在支气管肺泡灌洗液（BALF）样本中区分非重症和重症肺炎的临床应用尚未明确。因此，本研究旨在探讨mNGS对100名疑似肺炎个体的BALF样本的诊断性能，并将其与BALF样本的常规微生物学检测（CMT）和最终的临床诊断进行比较。最终临床诊断出27例非重症肺炎患者和73例重症肺炎患者。100例中，mNGS和培养的诊断性能表现出显着差异；65例样本类型相同，其中仅mNGS诊断阳性25例（38.46%），仅培养诊断阳性1例（1.54%）。此外，mNGS和培养均呈阳性的有24例（36.92%），mNGS和培养均呈阴性的有15例（23.08%）。在35例病例中，mNGS诊断出35例中有28例呈阳性，而间接免疫荧光法（IIFT）诊断出35例中只有4例呈阳性。此外，无论先前是否接触过抗生素，mNGS 的阳性率均高于培养阳性率。研究发现，重症肺炎患者的混合病原体明显高于非重症肺炎患者。重要的是，在仅通过 mNGS 诊断的 38 例患者中，医生根据 mNGS 结果改变治疗方案后，有 25 名患者的预后得到改善。总之，结果表明 BALF 的 mNGS 是检测重症肺炎混合病原体的潜在有效工具。