Haemophilus species

MICROBIOLOGY

• Small aerobic gram-negative coccobacillus found mainly in human respiratory tract.
• H. influenzae is the most notable species, but decline in past decades due to active childhood immunization (Hib).
  
  • Encapsulated, type b strain accounts for most bacteremic pneumonia and invasive disease, whereas non-encapsulated strains mostly cause otitis media, sinusitis, AECB and pneumonia.
  • Sensitivity of Gram stain and Cx probably ~50% in pts with H. influenzae pneumonia. Use of prior abx will decrease yield.
• Non-typeable H. influenzae strains more common now than type b. Other Haemophilus strains (H. aphrophilus, now called Aggretibacter aphrophilus) occasional cause of infection in HIV.