What is the role of bacteremia to the pathophysiology of Haemophilus influenzae type b (Hib) meningitis?

Updated: Jul 09, 2018
  • Author: Prateek Lohia, MD, MHA; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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Answer

Infection of distant sites appears to require the achievement of a degree of bacteremia sufficient to overcome the bacterial defense systems of the particular host. Clearance of bacteria from circulating blood is possibly more difficult for host defenses than containment of colonized bacteria. The capacity to eliminate Haemophilus from the circulation clearly entails normal function of the spleen as well as humoral and cellular arms of the immune system, because infections are more common in individuals who have defects in these systems.

In addition, preceding viral infections are possibly permissive of Haemophilus invasiveness (from colonized site to bloodstream or from bloodstream to target tissues) either because they disrupt barriers or they interfere with critical aspects of the host immune response. Upper respiratory infections or otitis media, presumably viral, often precede Haemophilus meningitis.

Once a sufficient degree of bacteremia is achieved, one or more sites may become infected. Predilection for a given site may be determined by proximity, blood flow characteristics, affinity of organisms for particular endothelial receptors, and the ability of organisms to pass through various barrier systems of the body.

Invasion of the central nervous system (CNS) may involve patterns of venous drainage from sites of nasopharyngeal colonization to vulnerable nearby CNS sites (eg, cribriform plate, thin sinus walls) or, more likely, high blood flow to sites of reduced blood-brain barrier (BBB) function (eg, choroid plexus).


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