# Epidemiology of Chlamydia pneumoniae infection in children with acute respiratory tract infections, Chengdu, 2022–2023

## TL;DR

This study tracks how Chlamydia pneumoniae infections in children changed in Chengdu from 2022 to 2023, showing higher infection rates after relaxed pandemic restrictions.

## Contribution

The study reveals how C. pneumoniae infection rates in children shifted with pandemic policy changes and seasonal patterns.

## Key findings

- C. pneumoniae IgM seropositivity increased from 4.3% in 2022 to 5.9% in 2023 after NPI relaxation.
- Females aged 3–14 years had higher seropositivity rates than males in 2023.
- Infection rates varied seasonally, with peaks in early 2023 and dips in late summer.

## Abstract

Chlamydia pneumoniae is a common pathogen involved in acute respiratory tract infections (ARTIs) in children.

Children with ARTIs attending the West China Second Hospital of Sichuan University from January 2022 to December 2023 were selected. IgM antibodies against Chlamydia pneumoniae (C. pneumoniae) were detected using a chemiluminescence immunoassay. Demographic and temporal differences in IgM positivity were compared between 2022 and 2023.

Over the two-year period, 20,689 children were included. In 2022, under stringent COVID-19 non-pharmaceutical interventions (NPIs), 453 positive and 10,092 negative cases, with IgM seropositivity rate of 4.3%. In 2023, following the nationwide relaxation of these NPIs, 602 positive cases, and 9,542 negative cases for IgM seropositivity rate of 5.9%, which was significantly higher than that in 2022 (P < 0.001). The IgM seropositivity rate of C. pneumoniae infection in children aged 3 to 14 years was significantly higher in 2023 than in 2022 (P < 0.05). The IgM seropositivity rate from January to May 2023 was significantly higher than that during the same period of 2022 (P < 0.001), while the IgM seropositivity rate from July to October 2023 was significantly lower than that during the same period in 2022 (P < 0.05). The IgM seropositivity rate in females aged 3 to 6 years was significantly higher than that of males in the same age group (P < 0.05). With the exception of 0- to 1-year-olds, the IgM seropositivity rates of females were significantly higher than those of males in the same age groups in 2023 (P < 0.05). Moreover, the IgM seropositivity rate of females was significantly higher than that of males in March, June, and September in 2022 (P < 0.05), and the IgM seropositivity rate of females was significantly higher than that of males in the same period in January, May, October, and November in 2023 (P < 0.05).

The results revealed that the epidemic trend and population susceptible to C. pneumoniae changed from 2022 to 2023, providing valuable insights into the prevention, diagnosis and management of C. pneumoniae infection in this region.