Detection of human coronavirus-OC43 in nasopharyngeal swab specimens via immunofluorescence staining using human serum and an anti-human antibody

Immunofluorescence methods to detect seasonal human coronavirus (HCoV)-OC43 in nasopharyngeal swab specimens using cell lines 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 with the combination of human serum containing the 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 the eleven patients in which HCoV-OC43 RNA was detected using the FilmArray method. Increased supernatant viral RNA levels 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 seventeen types and subtypes of respiratory viruses, including HCoV-OC43. The cells inoculated with the established strain HCoV-OC43 (ATCC VR-759) also showed positive staining. These findings suggest that the replication-competent HCoV-OC43 in the specimens could be detected via immunofluorescence staining of HRT-18 cells with human serum. It may be possible to obtain positive staining for viruses other than HCoV-OC43 using this method.