Fig. 2.

Reproducibility of the S. typhi Vi ELISA for specific IgG using sera from healthy donors (n = 11). Anti-S. typhi Vi IgG levels expressed in AU/ml for 11 healthy donors (hatched bars). Anti-S. typhi Vi IgG values are expressed as the mean AU/ml ± 1 s.d. over seven different assays. Two of the 11 (nos 10 and 11) had been vaccinated recently with S. typhi Vi vaccine and their sera used in assays 4–6 weeks post-vaccination. The reproducibility of the two internal QC sera (run in each assay) is indicated by the clear bars. The QC values were 22·1 ± 5·0 and 8·3 ± 1·5 AU/ml, respectively.