The Role of Encapsulation and Host Age in the Clearance of Haemophilus influenzae Bacteremia

Nonimmune rats given intravenous inoculations of 108 encapsulated Haemophilus influenzae type b cleared the bacteria at an exponential rate for 10 min; thereafter, the bacteremia plateaued at approximately 106 organisms/ml of blood. With 108 unencapsulated organisms, the initial clearance rate was significantly faster (P < 0.001) and was complete by 30 min. The rate of clearance of a mutant strain of H. influenzae type b containing 0.1% as much capsular polysaccharide as the wild type was significantly faster (P < 0.01), and H. influenzae type b from which a portion of the capsule had been removed physically had an intermediate clearance pat-