The current study advances our knowledge of the clinical features and epidemic trend of MP infection prior to and during the COVID-19 pandemic. Additionally, the analysis of clinical data spanning four years shows the epidemic trend under various preventive and control measures. Epidemic prevention strategies varied in various nations and areas, which may lead to different impacts in MP prevalence, and our findings indicated whether the prevalence of MP in southeast China was impacted. The mitigation of the COVID-19 pandemic has impacted the spread of endemic respiratory diseases and required drastic adjustments to population-level community behavior[13]. Both stringent NPIs and relaxed NPIs have contributed to reduce the spread of respiratory viruses including SARS-CoV-2, which has been confirmed by several studies, including RSV and influenza virus[13–14]. However, studies also showed that respiratory viruses were not always silent during the covid-19 epidemic. For example, our previous research showed that RSV became the main pathogen of LRTI during the pandemic, and there were different trend of susceptible population and epidemic season compared with those before the pandemic[12].
Different pathogens transmitted by respiratory droplets may have different prevalence trends during the COVID-19 pandemic. As the main pathogen of community-acquired pneumonia in children, MP has always been a matter of concern to pediatricians. Our study devoted to understand the prevalence and clinical characteristics of MP in hospitalized children during the pandemic. Through the study of a large sample for four consecutive years, this study not only summarized the changes in the seasonal distribution of epidemics, but also understood the demographic characteristics, disease severity in hospitalized children with LRTI infected with MP, which more comprehensively studied the prevalence and clinical characteristics of mycoplasma pneumonia in children before and during the pandemic, and provided certain information for the prevention and treatment strategies of MP in children in the future.
From 2019 to 2022, our study found that among hospitalized children with LRTI, the infection rate of MP was the highest in 2019, decreased to the lowest in 2020, and recovered to 20.6% in 2022, with statistical differences. It reflected the epidemic trend of MP infection for four consecutive years before and during the COVID-19 pandemic. According to the seasonal and monthly distribution of MP positive cases, there was a peak in the summer of 2019, which was similar with previous studies [10–11]. The recent MP outbreak is predicted to extend from the summer and fall of 2019 through the winter or spring of 2021, based on past trends[15]. However, compared to 2019, the positive instances of MP in 2020 and 2021 were significantly lower. Our findings also indicated a significant decline starting in February 2020, which was maintained at a low level with slight oscillations. Positive instances steadily increased until April 2022 and persisted till the conclusion of our investigation. Effective COVID-19 pandemic control strategies have the potential to significantly lower the prevalence of MP in closed or semi-closed populations, including hospitals, schools, religious centers, and military bases[16–18].The significant decline in 2020 was consistent with previous research[19]; similarly, investigations conducted in Finland and Japan showed that the prevalence of MP was significantly lower in 2020 as compared to 2012 and 2016[20–21]. It is plausible to speculate that the stringent protocols implemented to mitigate the spread of SARS-CoV-2 may have had a notable effect on other respiratory viruses that share comparable modes of transmission. NPIs like obligatory face masks, social isolation, stay-at-home orders, and hand hygiene were the main global initiatives. By reducing the spread of MP through droplets and contact through unclean hands and feet, all of these measures help. Therefore, during MP epidemic years, especially in, it was advised to practice adequate non-drug preventive isolation, such as mask wearing, frequent hand sanitization, and avoiding crowded areas. Our research also found that although it was still in the period of COVID-19 pandemic, MP positive cases gradually increased in 2022, and by the end of 2022, the number of positive cases even exceed the level of the same period in 2019. The reason for this may be related to the implementation of relaxed NPIs in Hangzhou in 2022, where children attend school and participate in activities normally; On the other hand, after a 2-year period of low infection proportion with MP, the population lacks immune protection and is generally susceptible to MP, resulting in a gradual increase in the number of positive cases.
From the perspective of age stratification, the majority of positive cases were preschool and school-age children, which was consistent with the characteristics of mycoplasma infection in children[14]. Comparing the four-year continuous data, the proportion of the 1–2 age group has a downward trend, while the proportion of the 7–12 age group has increased. In 2022, school-age children (7-12y) accounted for 50% of the positive cases, and the median age was also higher than that in the other three years, indicating statistical differences. In 2022, as the first year during the epidemic in which the infection rate of MP had gradually increased after a sustained low level of infection, the majority of cases were among school-age children, suggesting that school-age children are more susceptible to LRTI with MP Infection in a population with a generally decreased of immune protection against MP infection.I Compared with infants, the protection of school-age children is easily neglected, while school-age children are more susceptible to MP, which deserves our attention.
In terms of disease spectrum and severity, acute pneumonia dominated, accounting for 50.2 ~ 68.5%, and the proportion of severe pneumonia was also high. Except in 2020, a year with a extremely low MP infection rate, the proportion of severe pneumonia in other years was above 30%, and the higher the MP infection rate, the higher the proportion of severe pneumonia, suggesting that MP is an important pathogen of CAP in children and an important pathogen that causes severe pneumonia in children. In our study, with the four years, 8.9%-20.5% of children had co-infection with other pathogens. The co-infection rate was relatively low in 2021 and 2022, considering that it may be related to the selection of pathogens detected in this study, other common respiratory viruses, such as rhinovirus, coronavirus, metapneumovirus, etc., were not detected. The co-infection rate was also related to the prevalence of other viruses. For example, there were more mixed adenovirus infections in 2019, which was related to the prevalence of adenovirus in 2019 [22].
Compared with previous studies[10, 15], the nucleic acid test was performed to investigate the positive rate of MP in our study, which was more reliable than specific IgM antibody to diagnose the infection of MP, as the IgM antibody test results may be influenced by the time and duration of antibody production. In addition, our study period, which lasted from before the pandemic to the end of the pandemic, is meaningful for a comprehensive understanding of the prevalence of MP during the entire epidemic period. There were also some limitations in our study. First, in the first two years of the pandemic, especially in early 2020, when the NPIs was strictly implemented, the total cases of LRTI for admission was low, which may be related to delays in patients' visits to hospital emergency emergencies and face-to-face outpatient clinic, and it may create selection bias. Second, it is a single-center study, and it would be more convincing if the data was from different centers. In addition, our research did not cover the period after China relieved the prevention and control measures for category A infectious disease against SARS-CoV-2 infection, So it is not yet possible to determine the prevalence of MP after the end of the pandemic. Further research is needed to determine whether the prevalence of MP will return to the pre-COVID-19 characteristics after the end of pandemic.