The findings may reflect previous infections of patients with more than one viral strain, antibody cross-reactivity between strains due to HCoV group-specific rather than strain-specific antigens, better induction of mucosal IgA antibodies by certain HCoV strains and a shorter period of detectability after infection in secretions than in serum, and a better preservation of antibodies in the nasal wash specimens with antibody to HCoV than in those that had no detectable anti-HCoV antibody despite similar storage conditions.