# Epidemiological characteristics of single and co-infections with upper respiratory tract pathogens among children in eastern China: a retrospective study

## TL;DR

This study examines how common respiratory infections and co-infections vary by age in children in eastern China after pandemic restrictions were lifted.

## Contribution

The study provides detailed age-specific patterns of single and co-infections with seven respiratory pathogens in children post-pandemic.

## Key findings

- RSV was most common in infants, while M. pneumoniae and IAV increased with age.
- M. pneumoniae had the highest co-infection rates, often with HRV, ADV, and IAV.
- SARS-CoV-2 infections were most common in infants and school-age children.

## Abstract

The epidemiology of pediatric respiratory tract infections (RTIs) has shifted since the COVID-19 pandemic. This study aimed to characterize the prevalence and co-infection patterns of seven key respiratory pathogens in children in Eastern China following the relaxation of pandemic-related non-pharmaceutical interventions.

We conducted a large-scale, retrospective study involving pediatric patients aged under 18 years who presented with symptoms of acute respiratory tract infection (RTI) to a tertiary academic children's hospital between April 2,023 and March 2,024. Nasopharyngeal or oropharyngeal swab specimens were collected and tested using multiplex reverse transcription polymerase chain reaction (RT-PCR) for seven common respiratory pathogens: Mycoplasma pneumoniae (M. pneumoniae), adenovirus (ADV), influenza A virus (IAV), influenza B virus (IBV), human rhinovirus (HRV), respiratory syncytial virus (RSV), and SARS-CoV-2. Stratified analyses were performed across four predefined age groups.

Pathogen distribution showed distinct age-related patterns. Among high-risk pathogens, infants with RSV infection were the most common. Conversely, IAV and M. pneumoniae prevalence rose with age. Infants with IAV infection increased from 1,925 (9.1%) to 18,930 (17.5%) in school-age children with IAV infection, while Infants with M. pneumoniae infection surged from 2,812 (13.3%) to a peak of 48,284 (44.6%) in the oldest group with M. pneumoniae infection. For lower-risk pathogens, Children with ADV infection and those with IBV infection also increased steadily with age, reaching 20,661 (19.1%) and 11,574 (10.7%) respectively in school-age children. Toddlers with HRV infection peaked at 7,501 (14.0%), while Infants with SARS-CoV-2 infection were the most common (5,244, 24.8%), followed by school-age children with SARS-CoV-2 infection (12,331, 11.4%). Co-infections were significant, with children with M. pneumoniae infection being the most likely to have co-infections—frequently paired with HRV infection (2,143 children), ADV infection (1,100 children), and IAV infection (1,063 children).

The distinct epidemiological patterns and high rates of co-infection highlight the need for age-specific prevention strategies. The significant role of M. pneumoniae in both single and co-infections underscores the clinical utility of multiplex diagnostics to guide appropriate antimicrobial stewardship.

This study reveals significant age-dependent variations and high co-infection rates for seven respiratory pathogens in a large pediatric cohort. These findings are crucial for informing public health policies and optimizing the clinical management of pediatric RTIs in the post-pandemic era.