The prevention and treatment of AOM is one of the top priorities in our clinic. Recent studies revealed that viral infection of the respiratory tract, attendance of day-care centers and exposures to smoke have increased the likelihood of developing AOM4. It was reported that a lower incidence of otitis media with effusion was found in Italy, followed by restrictive anti-contagion measures14,15. In relative terms, there is a higher overall incidence of AOM and it is more closely related with respiratory tract infection in children, such as COVID-19. So far, few studies focus on additional assessment of the effects of social distancing on the incidence of AOM. We thus attempt to investigate the impact of activities parallel to daily living, including the COVID-19 lockdown, on the number of admissions for ENT-related AOM at a large pediatric ENT emergency department, located in Shanghai, China, from 2015 to 2020.
First, seasonality, along with climate change in the area is recognized as an important factor in the incidence of AOM16. In agreement with previous studies, seasonal fluctuation in the prevalence of AOM was observed in 2014–2019, with a peak in winter and a nadir in the summer. This may be related to the high incidence of upper respiratory tract infections in autumn and winter17. In autumn and winter, the influenza virus leads to a significant increase in upper respiratory tract infections and therefore results in a high incidence of AOM16–18.
Second, fewer outdoor social activities for children play a critical role in reducing the incidence of AOM in autumn and winter. It is worth noting that AOM prevalence dropped sharply (less than 300 children) in February every year from 2015 to 2019. Seasonally adjusted, the significant reduction of social gathering among children results in a lower prevalence of AOM in winter holidays (usually in February). The summer holidays (July and August) indicate another period of low AOM incidence, possibly due to higher temperature and relative social isolation on holiday.
In addition, social distancing, mask effects and good hand hygiene account for the decrease in the prevalence of AOM. A nationwide lockdown was imposed by the Chinese government in 2020 to prevent the spread of COVID-19. The compliance with hygienic-behavioral rules and restriction of unnecessary interpersonal contacts contributed to controlling the spread of diseases related to upper respiratory tract infection, besides COVID-1919–21. Social segregation, due to the outbreak of COVID-19, also caused a dramatic decline of AOM outpatient attendance, especially from February to August, when kindergartens and primary schools closed for home-based online teaching. After September, we have resumed our normal social and teaching activities in China, and the incidence of AOM increased significantly compared with the previous few months. But generally, the AOM outpatient attendance has dropped by more than 50% compared with that in the same period of previous years. It suggests that isolation effects caused by wearing masks could avoid or slow the spread of disease to some extent, which contributed to the major reduction of AOM cases.
Furthermore, this research also allowed analysis into AOM prevalence across different age groups, and found that children aged from 4 to 6 years had the highest incidence of the disease. Importantly, the incidence of AOM didn’t simply increase or decrease with age, and was involved in social and demographic factors. It was families that children spent most of their time with before 3 years old. Children aged 4–6 started school life gradually, along with more crowd gathering activities, and thus the AOM prevalence increased greatly. After age 7, children are less likely to get AOM, indicating changes in the fully-grown morphological structure of the eustachian tube and progressive maturation of the immune system22–24. Seasonal variations of AOM prevalence in children at different ages were also diverse. Even during non-epidemic periods, the incidence of AOM in school-age children was closely related to the semesters, which decreased significantly in winter and summer vacation. Therefore, there was a positive effect of social isolation on the AOM prevalence for school-age children. On the other hand, the incidence of AOM in preschoolers was more correlated with season variations, but not semesters.
Despite the importance of social segregation in preventing AOM prevalence, there are still several limitations in our study. For convenience, narratives are constructed from limited data in a single audiologic center. Importantly, our study is a retrospective and hospital-based analysis so possible bias and confounding may exist when some patients postponed or refused to go to the hospital due to the initial outbreak of COVID-19.