Application value of antibody titres and RNA detection in the early prediction of Mycoplasma pneumoniae pneumonia in children: a retrospective study
Authors: Tuo Wenbin , Guo Xia , Wu Mo , Xie Si , Shen Xin , Wang Jun , Cai Qinzhen , Yuan Chunhui , Yao Cong , Xiang Yun 
Published: April 2023

Abstract
Background
Children with Mycoplasma pneumoniae pneumonia (MPP) are prone to a missed diagnosis at the early stages of the disease, which greatly affects the prognosis of children. In this study, the application value of Mycoplasma pneumoniae (MP) antibody titres and RNA detection for diagnosing MP infection in children with community-acquired pneumonia (CAP) was evaluated. The present study aimed to seek appropriate detection methods and strategies for early rapid diagnosis in children with MPP.

Methods
A retrospective study was conducted on 563 paediatric patients aged 1 month to 15 years with CAP who were admitted to Wuhan Children’s Hospital, Tongji Medical College, Huazhong University of Science and Technology between July 2021 and February 2022. In all patients, throat swabs were collected for MP-RNA detection (simultaneous amplification and testing, SAT), and paired serum samples were collected for MP total antibody detection (particle agglutination, PA).

Results
The classification as MPP or non-MPP was based on clinical diagnosis, serum MP antibody titre, and clinical or laboratory evidence of infection by other pathogen(s). Among the 563 patients with pneumonia, 187 patients were in the MPP group, and 376 patients were in the non-MPP group. The Kappa values between the particle agglutination test at different titres (1:80, 1:160) and MP-RNA detection were 0.612 and 0.660 (P<0.01), and the consistency of the three methods was acceptable. When the single screening method was used, MP-RNA had the highest sensitivity (93.05%), while PA (1:160) had the highest specificity (100%). PA (1:80), with an area under the curve (AUC) of 0.822, was better than PA (1:160), with an AUC of 0.783, and there was a significant difference. When the combined screening methods were used, the AUC of MP-RNA parallel PA (1:160) was significantly higher than that of titres (1:80) (z=-4.906, P < 0.01). Except for MP-80, the efficacy of the other three test methods in females was slightly better than that in males. Among the differences in age distribution, PA (1:80) was slightly less effective in the 13–72 months age group than at other ages, and MP-RNA parallel PA (1:160) was slightly better than the younger age group (≤ 36 m). In the older age group (> 36 m), PA (1:160) was just the opposite, while MP-RNA was slightly better than other age groups in the 13–72 months age group.

Conclusions
For the diagnosis of MPP in children at the early of the disease, the antibody titre (1:160) parallel MP-RNA should be given preference, and then the disease should be further classified according to the antibody titre level and the age of the child. The combined application of the two detection methods could complement each other and strengthen the advantages, providing reliable laboratory evidence for the clinical diagnosis and timely treatment of MPP. When using the PA method alone to provide a reference standard to clarify MP infection, the differential diagnosis ability of 1:80 for MPP is better than 1:160, especially for children younger than 36 months.