What are Haemophilus influenzae infections?

Updated: Jul 02, 2019
  • Author: Joseph Adrian L Buensalido, MD; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Answer

Haemophilus influenzae is a small (1 µm × 0.3 µm), pleomorphic, gram-negative coccobacillus. Some strains of H influenzae possess a polysaccharide capsule, and these strains are serotyped into 6 different types (a-f) based on their biochemically different capsules. The most virulent strain is H influenzae type b (Hib). Some H influenzae strains have no capsule and are termed nonencapsulated H influenzae or nontypeable H influenzae (NTHi). The incidence of invasive Hib diseases has greatly decreased because of widespread use of the Hib conjugate vaccine, while NTHi strains have become the most common cause of invasive disease in all age groups in countries with routine Hib vaccination.


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