Comparison of H. influenzae strains R2866, HI2206, and HI2210 to sustain bacteremia in infant rats. (A) Bacteremic titers of rats infected with either R2866 (closed circles) or HI2206 (closed squares) in the virulence model of infection. (B) Competitive index showing the comparison of bacteria input ratios of R2866 and HI2206 on Day 0 compared to the output ratios on subsequent days of the infection. (C) Competitive index comparing the ∆hfq strain HI2206 and the complement HI2210. (D) Comparison of fitness of R2866 and HI2210. Data are representative of two independent experiments. (**P<0.0001; *P<0.01).