To explore the epidemiological characteristics of mycoplasma pneumoniae (MP) infection in children's respiratory from 2020 to 2021 in Guangzhou, and to observe the changes in the levels of peripheral blood lymphocyte subsets in infected children.

Serum mycoplasma pneumoniae antibody (MP-IgM) were collected from 17 453 children using indirect immunofluorescence assay (IFA) with respiratory tract infection who visited Guangdong Women and Children Hospital from January 2020 to December 2021. Among them, 443 children who were positive for MP-IgM and had undergone lymphocyte subset testing were selected as the observation group and control group. The levels of peripheral blood lymphocyte subsets (CD3⁺, CD19⁺, CD16⁺CD56⁺, CD4⁺, CD8⁺, CD4⁺/CD8⁺) were analyzed statistically.

Among the 17 453 children with respiratory tract infections, 4388 cases were positive for MP-IgM, with a total positive rate of 25.14%. The positivity rate of MP-IgM is highest in autumn (30.15%) and lowest in winter (19.54%); the positive rate of MP-IgM antibody remained at a high level from June to November, peaking in May. The positive rates of male and female children were 21.94% and 30.39%, respectively. The MP-IgM was lowest in the infant group (0~<1 years old), and highest in the preschool children (3~<7 years old). Among the eight respiratory tract infections, the highest positive rate for influenza virus B (IV-B) was 44% in the mixed infection with MP-IgM, while the lowest positive rate for chlamydia pneumoniae (CPn) was 1%. There were significant differences in the levels of CD4⁺, CD8⁺, CD4⁺/CD8⁺ between the observation group and the control group (P<0.01).

MP infection are most prevalent in autumn, with a higher positive rate in female children than in male children and a higher positive rate in preschool age children. Among the eight other respiratory tract infections associated with MP-IgM, the highest mixed infection rate was found for IV-B. The level of lymphocyte subsets can indicate the infection status. In clinical practice, strengthening the observation and treatment of the immune status of children can provide guidance for clinical medication and treatment.