Identification of influenza C virus in young South Korean children, from October 2013 to September 2016

BACKGROUND: Influenza C virus has been largely neglected, compared to influenza A orB viruses, and is not routinely tested in clinical practices. However, several studies have indicated that influenza C virus causes severe acute respiratory illness and pneumonia in all ages. OBJECTIVE: We conducted a study to identify influenza C virus among young children in South Korea.Study design. From October 2013 to September 2016, 973 young children with influenzalike illness (ILI) were enrolled at three university hospitals. We tested nasopharyngeal samples for 16 types of respiratory viruses. Among the tested samples, 564 were positive for one or more respiratory viruses. Except for the samples where 16 types of respiratory viruses were found, 409 negative samples were examined for the presence of influenza C virus, using a matrix gene specific primer set. RESULTS: Among 409 nasopharyngeal samples, five influenza C viruses were detected. The manifestation of influenza C virus infection in young children was observed acute respiratory illness, such as fever, rhinorrhea, and cough, but no pneumonia or severe respiratory illness. Nucleotide sequencing was conducted and a phylogenetic tree was generated. We found that C/Sao Paulo/387/82-like lineage viruses circulated in South Korea, and the fully sequenced virus (C/Seoul/APD462/2015) was closely related to C/Victoria/2/2012 and C/Tokyo/4/2014 strains. CONCLUSIONS: This study was the first report of influenza C virus detection in South Korea. Although severe illness was not observed in this study, we suggest the necessity for influenza C virus testing in pediatric patients with ILI, considering other reports of severe illnesses caused by influenza C virus infections.