Haemophilus influenzae

Gram Stain

• Gram negative coccobacilli small pleomorphic (facultative anaerobic)

Clinical Significance

This organism may represent a commensal of the flora from the nasopharynx, conjunctiva, and occasionally the genital tract.

It will often colonize the lower respiratory tract of patients with chronic obstructive pulmonary disease (COPD).

It can cause meningitis, epiglottitis, cellulitis (including periorbital cellulitis), septic arthritis, osteomyelitis, otitis media, sinusitis, acute exacerbation of COPD, pneumonia, empyema, conjunctivitis, bacteremia, neonatal and maternal sepsis, urethritis, cervicitis, and urinary tract infections (typically in children).

Usual Susceptibility Pattern

This organism is resistant to 1st generation cephalosporins and erythromycin.  Although clarithromycin and azithromycin have enhanced activity, they are not adequate for serious infections.

It has variable susceptibility to amoxicillin/ampicillin, TMP/SMX, and tetracyclines.  Note routine susceptibility testing may not detect all mechanisms of resistance to TMP/SMX.

Resistance to amoxicilin-clavulanate and cefuroxime is increasing. May not be detected if testing only for presence of beta-lactamase.

Most strains are susceptible to 3rd generation cephalosporins (including cefixime), quinolones, aminoglycosides, and rifampin.