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Haemophilus Influenzae

Haemophilus influenzae is a gram negative coccobacillus (short rod), which is non-motile, capsular and ong thread-like and pleomorphic in CSF specimen.


Route of Entry
H. influenzae infects humans only. It enters through the upper respiratory tract.

After entry of the organism, there are two fates:
•    Asymptomatic colonization
•    Infection

The organism produces IgA protease, which breaks down secretory IgA, therefore facilitating attachment to the respiratory mucosa.
Encapsulated variety enters blood stream and spreads to meninges. Non- encapsulated variety causes local infections.
The capsule of most lethal varieties is composed of polyribitol phosphate and is antiphagocytic. Endotoxin is lipopolysaccharide.

Virulence factors
•    Capsule
•    Endotoxin
•    IgA protease

Predisposing factors
•    Immunocompromised
•    Childrens 6 months to 6 years of age

Clinical symptoms
Symptoms of invasive infections include:

  • Meningitis
  • Fever
  • Headache
  • Stiff neck
  • Sepsis
  • Epiglottitis

Symptoms of local infections include:

•    Sinusitis
•    Otitis media
•    Conjunctivitis
•    Pneumonia

Lab- Diagnosis

•    CSF
•    Nasopharyngeal specimen
•    Pus
•    Blood


Features observed under microscope include:
•    Gram negative coccobacillus
•    Non-motile
•    Capsular
•    Long thread-like and pleomorphic in CSF specimen

Haemophilus influenzae on blood agar
Haemophilus influenzae on blood agar


Chocolate agar plus factor X (heme compound) plus factor V (NAD)
Mucoid colonies are formed. Factor X is required to produce essential enzymes e.g cyctochromes, catalases, peroxidases. Factor V is an electron carrier.

Biochemical tests

Biochemical tests are not usually done. B-biotypes are differentiated by indole, urease and ornithine decarboxylase tests.

Serological tests

•    Quelling reaction
•    Fluorescent- antibody staining
•    Counter-immunoelectrophoresis
•    Latex agglutination test.
•    PCR


  • Ceftriaxone
  • In case of local infection –amoxicillin– clavulanate is given.

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