Shifts in Bronchiolitis Viral Etiology and Seasonality Post-Pandemic: A Single-Center Retrospective Study
Introduction
Bronchiolitis, a common respiratory illness in infants and young children, has seen significant shifts in the viral pathogens responsible for its onset following the COVID-19 pandemic. Understanding these changes is crucial for healthcare providers to allocate resources efficiently and prepare for future trends.
Study Design and Participants
The study analyzednasopharyngeal swab samples from children hospitalized for bronchiolitis between January 2022 and December 2023. Participants were required to undergo nucleic acid testing for 13 respiratory pathogens, excluding those with incomplete medical records or certain underlying conditions that could affect their immune response.
Respiratory Virus Detection
Nasopharyngeal swab samples were processed using the TANBead OptiPure Virus Auto Tube to extract RNA, which was then stored at -80°C. Etiology was determined using a multiplex detection kit for 13 common respiratory viral targets, including influenza viruses, respiratory syncytial virus (RSV), and rhinovirus.
Ethics Statement
The study received ethics approval from the Research Ethics Committee of the Children’s Hospital of Zhejiang University School of Medicine. Data were collected retrospectively, anonymized, and stored in a standardized form.
Statistical Analysis
Statistical analysis focused on categorical variables using chi-squared tests and rank-sum tests. Logistic regression models were employed to assess the association between year and viral prevalence, adjusting for age and sex.
Results
Demographics
There were 697 cases of bronchiolitis among 2089 hospitalized children under 2 years old with lower respiratory tract infections. The median age was 7.5 months, with a higher proportion of boys (68.9%) than girls (31.1%). Post-pandemic, there was a significant increase in bronchiolitis admissions, particularly among children aged 12 to 18 months.
Viral Etiology
The study detected viral infections in 82.5% of the cases. RSV was the most common (43%), followed by HRV (24.5%), and PIV (8.6%). There were no significant differences in viral detection rates or mixed-virus infections between 2022 and 2023.
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Table 2 Distribution of pathogens diagnosis during two consecutive years 2022 and 2023 |
Age Stratification
The majority of patients were aged ≤6 months or 6–12 months. In younger children, RSV was the leading virus, while HRV was prevalent in older children aged 12–24 months. Admission rates increased across all age groups in 2023, with a notable rise in children aged 12 to 18 months.
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Figure 1 Proportion of different age groups and distribution of various viruses in bronchiolitis hospitalizations in 2022 and 2023. (A). Proportion of different age groups in 2022, (B). Proportion of different age groups in 2023, (C). Distribution of various viruses among different age groups in 2022, (D). Distribution of various viruses among different age groups in 2023. |
Viral Etiology and Gender
Male patients had a higher infection rate (68.9%) than females (31.1%). No significant differences were found in viral detection rates between genders, with RSV continuing to be the most prevalent.
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Figure 2 The distribution of viral infections among bronchiolitis hospitalizations by gender. (A) Male (B) Female. |
Seasonality
Before the easing of COVID-19 restrictions, bronchiolitis infections peaked in winter, specifically in December. Post-pandemic, there was an atypical seasonality with RSV infections showing an off-season outbreak in summer 2023. HRV trends remained stable, while HMPV and PIV peaks shifted.
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Figure 3 Monthly distribution of common respiratory viruses in 2022 and 2023. (A) Monthly distribution of bronchiolitis hospitalizations in 2022 and 2023. Monthly distribution of RSV-positive (B), HRV-positive (C), HMPV-positive (D), PIV-positive (E) cases in 2022 and 2023. |
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Figure 4 Adjusted Odds Ratios for RSV and PIV Infection by Season in Bronchiolitis Patients: A Subgroup Analysis (2022 vs 2023). (A) RSV infection, (B) PIV infection. |
Discussion
This study highlights shifts in bronchiolitis viral etiology and seasonality post-pandemic. RSV and PIV displayed significant variations in their epidemic patterns, indicating potential changes in transmission dynamics. These findings are crucial for future healthcare planning and intervention strategies.
Conclusion
Bronchiolitis admissions increased post-pandemic, with notable rises in children aged 12 to 18 months. RSV and HRV were the most prevalent viruses, with age-specific distribution trends. Seasonal variations in RSV and PIV infections suggest an unstable seasonal pattern, necessitating preparedness for atypical timing.
Abbreviations
RSV, respiratory syncytial virus; HRV, human rhinovirus; HBoV, human boca virus; PIV, parainfluenza virus; HMPV, human metapneumovirus; ADV, adenovirus; HCoV, human coronavirus; Inf, Influenza virus.
Acknowledgments
This research was supported by grants from the National Natural Science Foundation of China and other relevant health research centers.
Disclosure
The authors declare no conflicts of interest regarding the publication of this paper.
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