Haemophilus

Characteristics/Epidemiology

Normal flora in upper respiratory tract.

May also colonise conjunctiva and genital tract.

Most common strains are Hib and the unencapsulated.

Human is the only natural host

H. influenzae infection has dropped since vaccination.

 

 

Pathogenesis/Transmission

Capsule -> important virulence factor.

Most serious infection is related with capsule type b (Hib)

Transmission - by respiratory droplet

IgA protease - facilitate colonisation

Clinical significance

Contiguous spread (H. influenzae)

More often by unencapsulated

• Otitis media
• Sinusitis
• Epiglottitis - life-threatening
• Bronchopneumonia

Haematogenous spread (H. influenzae)

More often by Hib

• Septic arthritis
• Cellulitis
• Bacterial meningitis, often with otitis media

H. aegyptius (aka H. influenzae biotype, or Koch-Weeks bacillus)

   -> can cause outbreaks of purulent conjunctivitis

   -> can also cause Brazilian purpuric fever

H. ducreyi

   -> cause chancroid (soft chancre) (STD)

   * painful genital lesions + inguinal lymphadenopathy

   -> formation of bubo (swollen lymph node) -> suppuration

Laboratory identification

Pleomorphic

May have capsule (6 types) or uncapsulated.

Cultured on chocolate agar (growth requires X factor (hemin) and V factor (NAD+))

Capsular type can be tested by Quellung reaction or by immunofluorescent staining.

Treatment

Need to test sensitivity

First line for non-life threatening: Ampicillin+sulbactam

First line for life-threatening: cefotaxime, ceftriaxone

Second line: trimethoprim+sulfamethoxazole

Azithromycin for H. ducreyi infection

Prevention/immunity

Active immunisation

Given for children <2 y.o.

• Made up of Hib polyribose phosphate (PRP) capsular carbohydrate conjugated with a carrier protein
• 2 types of carrier protein:
  * OMP (outer membrane protein of N. meningitidis)
     -> effective after first dose, require 3 doses altogether
  * other carrier protein
     -> not as effective, requires 4 doses altogether

Rifampicin given for prophylaxis in close contacts

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Things to revise/add later:

Bibliography:

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