Discussion:
This is an observational study evaluating the respiratory sequelae following COVID-19 infection in Thai healthy children aged 7-18 years. The main findings of our study revealed that a quarter of the patients had at least one post COVID symptom which significantly associated with the history of COVID-19 pneumonia. Pulmonary function impairment was found in almost one-fifth of the patients and the obstructive impairment was the most common. However, no clinical characteristics were identified as a significant factor associated with the presence of pulmonary function impairment and changes in pulmonary function measures.
The prevalence of post COVID-19 symptoms in our study is consistent with previous literatures which ranged between 23-27%12,13,14. In addition, fatigue, dyspnea and cough are common symptoms in our study and consistent with findings in other studies14,15. These outcomes are likely to indicate that post COVID-19 symptoms are comparable across countries despite variations in management; and after recovering from COVID-19 infection ongoing follow-up for the patients is necessary despite their lack of remarkable medical backgrounds.
Pneumonia which represents the moderate severity of acute COVID-19 infection, was the only factor associated with respiratory sequalae. Approximately, half of our patients with COVID-19 pneumonia had at least one post COVID-19 symptom. This finding consolidates previous evidence that patients suffering more severe infections or requiring intensive care, are more susceptible to post COVID-19 symptoms, ranging from 30-70%13,15,16,17. This could be straightforwardly explained by infection-related and cytokine-induced airway and lung damage15,16. Therefore, children who have been diagnosed with COVID-19 pneumonia are at a higher risk and in needs of careful follow-up evaluation. The additional evaluation should include both clinical review and pulmonary function tests.
Among the participants, almost one-fifth exhibited impaired pulmonary function, with obstructive impairment being the most prevalent, followed by possible restrictive impairment. Our findings aligned with existing studies which reported impaired pulmonary function in the patients from 0-24%7,14,16,18,19,20. The wide range of the prevalence of impaired pulmonary function after COVID-19 infection could be explained by multiple reasons, for example children’s medical backgrounds and the timepoint of pulmonary function assessment. In the previous study Palacios et al study, it was found that children who had pre-existing conditions such as asthma and obesity exhibited a higher incidence of pulmonary abnormalities7. They also reported that the rate of abnormal pulmonary function declined from 24% to 10% over a nine-month follow-up period, which could be a result of either natural healing process or the use of inhaled corticosteroids to treat bronchial hyperresponsiveness7.
Our research revealed no significant correlation between post COVID symptoms or COVID-19 pneumonia and impaired pulmonary function, corresponding with earlier research16. Nevertheless, around 15% of the participants who were diagnosed with COVID-19 URI and did not exhibit persistent symptoms after the infection showed abnormal spirometry results, mainly compatible with obstructive impairments. Probably, this is a consequence of chronic subclinical inflammation of peripheral airways caused by COVID-19, regardless of infection severity21,22. These findings highlight the importance of undertaking pulmonary function tests in patients with COVID-19 infection to evaluate their post-infection progression.
Although this study provides additional data and highlights the importance of monitoring pediatric patients after COVID-19 infection, there are some limitations. First and foremost, the sample size was small as this study was undertaken in a single center. For assessing the respiratory sequalae, we relied on clinical review and spirometry and did not include computed tomography chest imaging, so we were unable to address lung parenchymal changes such as pulmonary fibrosis. Moreover, lung volume and diffusion capacity of the lungs were not routinely measured, so we could not provide additional data on other functional consequences of COVID-19 infection. Finally, this is a cross-sectional study without ongoing evaluations for both post COVID-19 symptoms and pulmonary function. We cannot ascertain whether the respiratory sequalae persist over time or resolve spontaneously. Henceforth, further studies are warranted to fill the gaps and improve the understanding of post COVID conditions in children.