Representative indirect immunofluorescent assays of Vero E6 cells infected with thrombocytopenia syndrome virus from patients in rural areas, South Korea. Indirect immunofluorescent assays were conducted by using serially diluted patient serum as primary antibody and fluorescein isothiocyanate–conjugated antihuman IgG as secondary antibody. A) H1 serum (negative, dilution 1:32, IgG titer <1:32); B) B321 serum (positive, dilution 1:64, IgG titer 1:512); C) H214 serum (positive, dilution 1:32, IgG titer 1:128); D) D127 serum (positive, dilution 1:32, IgG titer 1:256). Original magnification x400.