Haemophilus influenzae

Background

Microbiology

• Species of Gram-negative bacillus within the genus Haemophilus
• Deficient heme biosynthetic pathway leading to X-factor-dependent growth on media
• Fastidious growth with standard media
• May be encapsulated; non-encapsulated strains are referred to as "nontypeable"
• The group includes Haemophilus influenzae, Haemophilus aegyptius, and Haemophilus haemolyticus

Test	Biotype
	I	II	III	IV	V	VI	VII	VIII
Indole	+	+	–	–	+	–	+	+
Urease	+	+	+	+	–	–	–	–
ODC	+	–	–	+	+	+	–	–

Clinical Manifestations

• Community-acquired pneumonia, particularly in children, meningitis, bacteremia, mainly type b strains
• Community-acquired pneumonia, acute otitis media, acute sinusitis, acute exacerbation of COPD, mainly untypeable strains

Management

• For beta-lactamase-negative strains, ampicillin is recommended
  • Generally still considered resistant to first-generation cephalosporins
• For beta-lactamase-positive strains, ceftriaxone or cefepime
• Alternatives include chloramphenicol, ertapenem, meropenem
• Possibly also a fluoroquinolone, azithromycin, clarithromycin, doxycycline, amoxicillin-clavulanic acid
• Duration depends on syndrome being treated:
  • Uncomplicated meningitis: 10 days
  • Pneumonia: at least 5 days, with clinical improvement
  • Septic arthritis: 10 to 14 days
  • Pericarditis: 3 to 6 weeks
  • Empyema: 3 to 6 weeks
  • Osteomyelitis: 3 to 6 weeks

Further Reading

• Antimicrobial Resistance in Haemophilus influenzae. Clin Microbiol Rev. 2007. doi: 10.1128/CMR.00040-06