Preplanned Studies: Trends in Respiratory Infectious Pathogens in Children Under the Age of 14 — Xiamen City, Fujian Province, China, 2017–2023

Respiratory tract infections (ICD-10/J00-J99) are infectious diseases caused by various microorganisms, including bacteria, viruses, mycoplasmas, fungi, and parasites. These infections are typically seasonal and have been extensively studied. The implementation of dynamic control measures in China from 2020 to 2023 may have helped reduce the spread of other respiratory pathogens. Certain regions have experienced a delayed outbreak of respiratory viruses due to these interventions (1–5). However, most existing studies have mainly focused on the period from 2020 to early 2022. Timely surveillance is crucial for understanding community health threats, especially when observed trends deviate from seasonal norms. This study aims to assess changes in the epidemiological trends of common respiratory pathogens among children in recent years. We conducted a retrospective analysis of the prevalence of various common respiratory pathogens among patients with respiratory infections admitted to the Women and Children’s Hospital, School of Medicine, Xiamen University, in Fujian Province from 2017 to 2023.

The study was conducted at the Women and Children’s Hospital, School of Medicine, Xiamen University, which serves as a regional medical center for maternal and child healthcare in southwestern Fujian. The study retrospectively analyzed pediatric patients with respiratory tract infections who visited the hospital between January 1, 2017, and November 30, 2023. The inclusion criteria included children tested for pathogens (bacteria, virus, or mycoplasma) and excluded those above 14 years old or who didn’t undergo pathogen testing. The study focused on detecting five viruses [Respiratory syncytial virus (RSV), adenovirus, influenza A (Flu A), influenza B (Flu B), parainfluenza], five bacteria (H. influenzae, M. catarrhalis, S. pneumoniae, S. aureus, K. pneumoniae) and Mycoplasma pneumoniae. The five viruses were detected by polymerase chain reaction (PCR) capillary electrophoresis fragment analysis (multiple detection kits for 13 types of respiratory pathogens, Ningbo Health Gene Technologies Co., Ltd, Ningbo, China), probe-based PCR (Respiratory virus nucleic acid six-fold test kit, Beijing Zhuo Cheng Hui Sheng Biotechnology Co., Ltd., Beijing, China) or immunofluorescence (D®³ Ultra DFA Respiratory Virus Screening and ID Kit, Diagnostic Hybrids Inc., Athens, USA) with nasal swabs. Mycoplasma pneumoniae was detected by Probe-based PCR (Mycoplasma pneumoniae nucleic acid test kit, Daan Gene Co., Ltd, Guangzhou, China). Sputum was tested for typical bacteria using conventional culture method. A total of 25,506 virus detection samples, 21,640 bacterial detection samples, and 23,579 pneumonia detection samples were collected. Trend analysis was conducted using GraphPad Prism and ArcGIS.

According to the current addresses of the patients included in the study, the majority (77.71%) were from Xiamen, while 18.38% were from other cities in Fujian Province, and 3.91% were from other provinces (Figure 1A). The annual distribution of these samples is shown in Figure 1C. The number of outpatient visits for respiratory infections exceeded one hundred thousand from 2017 to 2019, decreased in 2020 and 2021, and then increased again in 2022 and 2023 (Figure 1B). The prevalence of various viruses declined between 2019 and 2023. However, cases of some pathogen infections have returned to previous levels, and in some cases, have even exceeded previous levels. Of particular note is the unprecedented surge in cases of Mycoplasma pneumoniae in recent months.

Figure 1. 

Information on the population and tested samples included in this study. (A) Distribution of patient sources included in this study; (B) total outpatient visits and visits for respiratory symptoms in the hospital over the past 7 years; (C) Number of samples tested for viruses, bacteria, and Mycoplasma pneumoniae in the last seven years.

Abbreviation: RTI=respiratory tract infection, MP=Mycoplasma pneumoniae.

As previously described, there have been changes in the epidemiology of respiratory infections in recent years. Our study observed a significant reduction in circulating respiratory pathogens, including major viruses, bacteria, and mycoplasma, in early 2020. Subsequently, several viruses demonstrated a “peak” pattern over the following three years, while bacteria did not exhibit such a pattern. Respiratory syncytial virus (RSV) emerged as the predominant virus in pediatric respiratory infections, with a surge in infections occurring after 2020, resulting in an infection peak higher than usual in July 2021 (Figure 2A). Adenovirus did not display a distinct seasonal pattern. Although a relatively large number of infected patients and increase in positive rates were seen in the summer of 2019, the number of infections has remained low in subsequent years. However, in recent months, there has been a steady increase in the number of adenovirus infections and positive rates, surpassing the previous years’ levels (Figure 2C). Before 2020, influenza A and influenza B traditionally alternated in dominance. In 2020 and 2021, the number of influenza A and influenza B infections was low. However, in the 2022–2023 period, influenza B re-emerged, while influenza A experienced two peaks, with a higher number of infections than the pre-March 2020 timeframe. Notably, both the number of influenza A and B infections and positivity rates rose simultaneously last month (Figure 2E, 2G). Since the winter of 2020, there has been a significant increase in parainfluenza infections and positive rates (Figure 2I). Among the five bacteria of interest (H. influenzae, M. catarrhalis, S. pneumoniae, S. aureus, K. pneumoniae), there was no observable trend of post-decline “upsurge” (Figure 2B, 2D, 2F, 2H, 2J). The last significant outbreak of Mycoplasma pneumoniae occurred in 2019. After 2020, Mycoplasma pneumoniae infections remained at low levels until the second half of 2023. However, in the past two months, there has been a remarkable surge in Mycoplasma pneumoniae infections and positive rates, making it the primary pathogen in respiratory infections in 2023 (Figure 2K, 2L). It is important to note that cases where pathogenic microorganisms were not detected or could not be identified among patients were not included in Figure 2L.

Figure 2. 

Changes in positive samples for different pathogens in the last seven years. (A) RSV; (B) H. influenzae; (C) Adenovirus; (D) M. catarrhalis; (E) influenza A; (F) S. pneumoniae; (G) Influenza B; (H) S. aureus; (I) Parainfluenza; (J) K. pneumoniae; (K) Mycoplasma pneumoniae; (L) Percentage of positive samples infected with different respiratory pathogens in different years (Number of positive samples for different pathogens divided by the sum of positive samples for all pathogens).

Abbreviation: RSV=respiratory syncytial virus.