Based on the much lower frequency of patients with HCoV-specific IgA antibody in nasal wash specimens than of those with IgG in serum in our older adult population, one might hypothesize that antibodies to HCoV in nasal secretions decline in titer more rapidly after infection than do serum antibodies or that infection does not induce IgA antibody to HCoV in nasal secretions to high titers or at all in a significant proportion of older, chronically ill patients with COPD.