Severe viral infection Unusual viral infection Severe seasonal coronavirus infection Severe HCoV infection Severe HCoV-NL63 infection A severe seasonal coronavirus infection can be a manifestation of unusual susceptibility to infection, particularly in T-cell deficiencies and post-hematopoietic-stem-cell-transplant patients. Severe common cold coronavirus infection Invasive seasonal coronavirus infection A severe infection caused by a seasonal coronavirus (HCoV-229E, HCoV-OC43, HCoV-NL63, or HCoV-HKU1), characterized by lower respiratory tract involvement, hypoxia, or systemic illness beyond that typically seen with these viruses in immunocompetent hosts. Severe HCoV-HKU1 infection Severe HCoV-OC43 infection Severe HCoV-229E infection