Abstract: Objective To explore the diagnostic value of metagenomics next-generation sequencing (mNGS) of bronchalveolar lavage fluid (BALF) for mixed infection in children with severe Mycoplasma pneumoniae pneumonia (MPP). Methods From June 2019 to December 2019 , children with severe MPP who need bronchoalveolar lavage treatment were enrolled. BALF was detected by traditional pathogen detection and mNGS at the same time. BALFs were sent for traditional pathogen detection and metagenomics next-generation sequencing. The diagnostic efficacy of the two detection methods for the mixed infection in severe MPP was analyzed. Results A total of 47 ( 23 males and 24 females) children with severe MPP were enrolled and median age was 58 . 0 ( 38 . 0 ~ 81 . 0 ) months. Radiography showed pulmonary consolidation/atelectasis in 31 cases, pleural effusion in 10 cases, and pneumomediastinum in 2 cases. Bronchoscopy revealed that 28 children had obvious mucosal necrosis, poor ventilation, or phlegm formation. The BALF of 47 children was detected by both traditional pathogen detection and mNGS detection, and both methods detected that all children were Mycoplasma pneumoniae positive. Traditional pathogen detection of BALF found mixed infection in 2 cases (4.3%). By mNGS detection, mixed infection was found in 23 cases (48.9%), which was significantly higher than that in traditional pathogen detection. The difference was statistically significant (P< 0 . 001 ). The top three pathogens detected by mNGS were adenovirus type 7 ( 11 cases, 23 . 4 %), Streptococcus pneumoniae ( 5 cases) and Mycobacterium abscess ( 5 cases). Conclusions The BALF mNGS has a higher detection rate of mixed infection in pediatric severe MPP than traditional detection methods, especially for the detection of combined virus infection. It is helpful for early virus typing and viral load analysis.

Key words: bronchoalveolar lavage fluid;? metagenomic next-generation sequencing;? severe Mycoplasma pneumoniae pneumonia; mixed infection