Haemophilus haemolyticus: a human respiratory tract commensal to be distinguished from Haemophilus influenzae

J Infect Dis. 2007 Jan 1;195(1):81-9. doi: 10.1086/509824. Epub 2006 Nov 27.


Background: Haemophilus influenzae is a common pathogen in adults with chronic obstructive pulmonary disease (COPD). In a prospective study, selected isolates of apparent H. influenzae had an altered phenotype. We tested the hypothesis that these variant strains were genetically different from typical H. influenzae.

Methods: A prospective study of adults with COPD was conducted. Strains of apparent H. influenzae obtained from a range of clinical sources were evaluated by ribosomal DNA sequence analysis, multilocus sequence analysis, DNA-DNA hybridization, and sequencing of the conserved P6 gene.

Results: Variant strains were determined to be Haemophilus haemolyticus by means of 4 independent methods. Analysis of 490 apparent H. influenzae strains, identified by standard methods, revealed that 39.5% of sputum isolates and 27.3% of nasopharyngeal isolates were H. haemolyticus. Isolates obtained from normally sterile sites were all H. influenzae. In a prospective study, acquisitions of new strains of H. haemolyticus were not associated with exacerbations of COPD, whereas 45% of acquisitions of new strains of H. influenzae were associated with exacerbations.

Conclusions: Standard methods do not reliably distinguish H. haemolyticus from H. influenzae. H. haemolyticus is a respiratory tract commensal. The recognition that some strains of apparent H. influenzae are H. haemolyticus substantially strengthens the association of true H. influenzae with clinical infection.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Haemophilus / classification*
  • Haemophilus / isolation & purification*
  • Haemophilus Infections / epidemiology
  • Haemophilus Infections / microbiology*
  • Haemophilus influenzae / classification
  • Haemophilus influenzae / genetics
  • Haemophilus influenzae / isolation & purification
  • Humans
  • Phylogeny
  • Pulmonary Disease, Chronic Obstructive / complications*
  • Respiratory Tract Infections / microbiology*
  • Sputum / microbiology