FIG. 5.

Survey of serum anti-F. tularensis antibody levels in Germany (n = 6,632). The distribution of ELISA results stratified by a cutoff level of 0.200 (line a) and results of confirmatory Western blotting are shown. Line b indicates the threshold value of confirmed positive samples. For calculation of specificity, sera with values between lines a and b (n = 18) were considered true negatives by ELISA, since all of them were negative by Western blotting. All serum samples were diluted 1/250. The cutoff was determined by 200 independent measurements of the negative-control serum and calculation of the range of values equal to 3 times the standard deviation. For a better overview, results for only 1/50 of the serum samples without subsequent Western blotting, randomly selected, are given.