What causes 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

Of the encapsulated H influenzae strains, serotype b is the most virulent. Most invasive Haemophilus infections are caused by encapsulated strains , in particular Hib. Unencapsulated strains rarely cause bacteremia; these species are more likely to produce noninvasive infections (eg, sinusitis, otitis media).

In the prevaccination era, Hib accounted for more than 95% of all cases of H influenzae meningitis. Most human diseases are caused by a limited clone complex of Hib strains that appear to have achieved worldwide distribution as the result of historical migrations of human hosts. These clones express in their capsules a repeating polymer of PRP that has been shown to be a particularly important virulence factor.

It remains important to recognize and treat unencapsulated and therefore nontypeable H influenzae (NT-HI) infections, against which Hib vaccine provides no protection. Factors that predispose to systemic infection with NT-HI include the presence of cerebrospinal fluid shunts, posttraumatic compromise of the blood-brain barrier (as with post-traumatic encephalocele), and central nervous system implants. [1]


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