FIG 3.

Elevated SBA and OPKA levels in serum are associated with decreased disease severity after Shigella infection. SBA (A) and OPKA (B) titers in EcSf2a-2 vaccine recipients (n = 15) and nonvaccinated controls (n = 13) were correlated with disease index (DI) postchallenge using Spearman's rank correlation (r and P values are indicated on the plots). The DIs after challenge were as follows: 6 of 28 volunteers remained healthy (DI of 0), 8 of 28 had mild disease (DI of 1), 8 of 28 experienced moderate disease (DI of 2), and 6 of 28 were severely ill (DI of 3). Titers were further grouped and compared based on disease severity (healthy to mild disease, DI of 0 or 1; moderate to severe disease, DI of 2 or 3) by using the Mann-Whitney U test (C and D). Asterisks indicate significant differences between groups at a P of ≤0.05.