Etiology and Epidemiology of Croup before and throughout the COVID-19 Pandemic, 2018-2022, South Korea

Abstract

Omicron, a recent variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is currently globally dominating. We reviewed the etiology and epidemiology of croup over an approximately 5-year period, with an emphasis on the recent dominance of the Omicron variant. Children less than 5 years of age seen in the emergency department with diagnosis of croup from two large national tertiary hospitals were collected for the period from January 2018 through March 2022. Viral etiologies of the patients were compared with national surveillance data upon circulating respiratory viruses in the community. A total number of 879 croup cases were recognized during the study period. The most common pathogen was SARS-CoV-2 (26.9%), followed by HRV (23.8%), PIV1 (14.6%), PIV3 (13.1%), and CoV NL63 (13.1%), among seventeen respiratory viral pathogens tested by polymerase chain reaction. The viral identification rate was significantly higher in the Omicron period, with most of the pathogens identified as SARS-CoV-2. In the Omicron period, with the exponential increase in the number of COVID-19 cases in the community, croup associated with SARS-CoV-2 significantly increased, with a high detection rate of 97.2% (35 of 36) among croup cases with pathogen identified. The etiologic and epidemiologic data before and throughout the COVID-19 pandemic indicate that the association between croup and infection with the SARS-CoV-2 Omicron variant is highly plausible.

Keywords: COVID-19; child; croup.

Figure 1

Proportional distribution of viral pathogen in children responsible for croup during 2018–2022, South Korea. PIV, parainfluenza virus; HRV, human rhinovirus; CoV, coronavirus; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

Figure 2

Epidemiologic curve of croup patients from two tertiary hospitals with surveillance data of parainfluenza viruses and coronaviruses, including severe acute respiratory syndrome coronavirus 2 circulating in the community, 2018–2022, South Korea. The broken line indicates circulating respiratory viruses in the community collected from the Laboratory Surveillance Service (Korea Disease Control and Prevention Agency, https://www.kdca.go.kr/ accessed on 12 September 2022). The blue dashed line indicates the mean numbers of weekly SARS-CoV-2 confirmed cases (Korean Ministry of Health and Welfare, http://ncov.mohw.go.kr/en, accessed on 1 August 2022). All lines correspond to the y-axis on the left. Each bar shows croup cases from study sites. Croup cases with detection of parainfluenza virus or coronavirus are correspondently colored. The gray bar indicates croup cases with other or unknown etiology. Each bar corresponds to the y-axis on the right. The left y-axis corresponding to viral surveillance data is presented on a logarithmic scale. COVID-19, coronavirus; PIV, parainfluenza virus; CoV, coronavirus; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.