Detection of Human Coronavirus-OC43 in Nasopharyngeal Swab Specimens Via Immunofluorescence Staining Using Human Serum and an Anti-human Antibody

Immunofluorescence methods using cell lines to detect seasonal human coronavirus (HCoV)-OC43 in nasopharyngeal swab specimens have not yet been established. A human rectal adenocarcinoma cell line (HRT-18) was exposed to the specimens obtained from patients with upper respiratory tract infections. Immunofluorescence staining was conducted using a combination of human serum containing an HCoV-OC43 anti-spike protein antibody and a fluorescence-labeled anti-human antibody. Positive staining in HRT-18 cells was detected after exposure to specimens obtained from nine of eleven patients in whom HCoV-OC43 RNA was detected using the FilmArray method. Increased viral RNA levels in the supernatant were also detected in HRT-18 cells exposed to specimens obtained from four of five patients. In contrast, positive staining was not detected in HRT-18 cells exposed to six patient specimens that tested negative for RNA from 17 types and subtypes of respiratory viruses, including HCoV-OC43. Cells inoculated with the established strain HCoV-OC43 (ATCC VR-759) also showed positive staining. These findings suggest that replication-competent HCoV-OC43 in the specimens can be detected via immunofluorescence staining of HRT-18 cells with human serum. Using this method, positive staining for viruses other than HCoV-OC43 may be obtained.