Potential subgroups of interest, suggestive of bacterial infection, include participants with (a) an elevated C-reactive protein (CRP) level, (b) double-sickening, defined as, “Have you had worsening of sinus symptoms after initial improvement,” (c) evidence of nasal discharge purulence on clinical examination, (d) change in smell (cacosmia), (e) pain in the teeth, or (f) provider’s clinical impression [21,25–30]. Here, CRP is linked to bacterial infectious disease.