The occurrence of infection-related systemic diseases in Korean children and adolescents has decreased after the spread of the COVID-19 pandemic: A multicenter retrospective study

Background: The occurrences of infection-related systematic diseases, such as Henoch-Schönlein Purpura (HSP), intussusception, and mucocutaneous lymph node syndrome (MCLS) may have decreased, similarly to the decreased occurrence of infectious diseases following the Coronavirus disease 2019 (COVID-19) pandemic. We aimed to investigate whether there was a change in the occurrence of these diseases in South Korea after the spread of the COVID-19 pandemic. Methods: In this multicenter, retrospective study conducted in 16 medical centers in South Korea patients diagnosed with HSP, intussusception, and MCLS at the age of <18 years between January 2016 and December 2020 were included. New occurrences of these three diseases were investigated monthly and annually, while to compare between the pre- and post-COVID-19 era cases, new occurrences between 2017-2019 and 2020 were compared. Additionally, the total annual occurrence rate was calculated by dividing each center's occurrence into the annual population per 100,000 of the population <18 years in each region that the center covers. Results: A total 6,857 patients were included in this study. From 2017 to 2020, the number of patients diagnosed with HSP, intussusception, MCLS at the age of <18 years were 1,301, 1,693, and 3,863 patients, respectively. The average number of patients during the three years before the COVID-19 pandemic were each 379.7, 505.3, and 1,112.0 for HSP, intussusception, MCLS, respectively, which each decreased by 57.3%, 65.0%, 52.6% to 162, 177, 527 in 2020, respectively. Furthermore, the total annual occurrence rate showed a significant decrease in 2020 compared to 2017 to 2019 in all three diseases (2017-2020; HSP: 11.85, 12.96, 10.52, and 5.48; intussusception: 13.94, 16.97, 16.31, and 5.98; MCLS: 33.89, 35.11, 34.69, and 17.82, respectively). Conclusions: We revealed that the occurrence of HSP, intussusception, and MCLS, which are representative of infection-related systemic diseases in the pediatric population, decreased significantly after the spread of the COVID-19 pandemic.