II. Pathophysiology
- Haemophilus Influenzae
- Facultatively anaerobic Gram Negative Rods (or coccobacilli) in family Pasteurellaceae
- Non-motile and Non-Spore forming
- Respiratory transmission
- Haemophilus is derived from the greek "blood loving"
- Cytochrome system within Haemophilus organisms require Hematin (or Factor X, from blood)
-
Polysaccharide Capsule
- Capsule confers virulence and is composed of Polyribitol Ribose Phosphate (PRP)
- Six different capsule types (A, B, C, D, E, F)
- Capsule Type B (Hib)
- Capsule Type B is most important in humans (esp. in children) and the Hib Vaccine target (see below)
- Encapsulated Haemophilus Influenzae (esp. Hib) is a significant risk for Sepsis in Asplenic patients
- Haemophilus Influenzae Type B is associated with invasive disease in children (e.g. Bacterial Meningitis)
- Hib invasive disease has been dramatically reduced in the U.S. by Hib Vaccine
- Non-Encapsulated Strains (Non-Typeable Haemophilus Influenzae, NTHi)
- Non-Typeable strains colonize the upper respiratory tract of children and adults
- Responsible for most Haemophilus Influenzae infections in adults and vaccinated children
- Low virulence organisms (lacking a capsule)
- Includes strains previously classified as separate species (now considered non-typable H. Influenzae)
- Haemophilus aegyptius (causes Bacterial Conjunctivitis, Brazilian Purpuric Fever)
- Haemophilus haemolyticus (rare Immunocompromised infections, including endocarditis)
- Typically NTHi causes only local disease (e.g. Otitis Media, Acute Sinusitis)
- Invasive disease (e.g. Pneumonia) may occur in age over 65 years or Immunocompromised patients
III. Associated Conditions: Haemophilus Influenzae Infections
- Haemophilus Influenzae Type B or Hib (Non-Immunized Children)
- Haemophilus Influenzae Pneumonia
- Hib Vaccine has nearly eliminated Hib Pneumonia in Children
- NTHi in adults now predominates as a Bacterial Pneumonia cause (see below)
- Prior to Hib Vaccine, Hib Pneumonia in Children 0–4 years of age caused significant morbidity and mortality
- Developed countries: 6 per 100,000 cases (5% mortality)
- Developing Countries: 300 per 100,000 cases (13 to 24% mortality)
- Hib Vaccine has nearly eliminated Hib Pneumonia in Children
- Occult Bacteremia (Pediatric Fever Age Under 3 Years)
- Vaccines (Hib, PCV) have reduced Occult Bacteremia in febrile children <36 months from 12% to 2%
- Bacterial Meningitis
- Hib was the most common cause of Bacterial Meningitis in age 6 months to 3 years prior to Hib Vaccine
- Hib Meningitis was previously 10,000 cases/year (now rare in U.S. after 1987 Hib Vaccine introduction)
- Significant neurologic deficits persisted in 50% of Antibiotic treated children (of the 95% that survived)
- Septic Arthritis
- Hib was the most common cause of Septic Joint in infants prior to Hib Vaccine
- Hib now (post-Hib Vaccine) represents <3% of Septic Arthritis cases
- Acute Epiglottitis
- High mortality condition, now rare in children since Hib Vaccine introduction
- Hib Epiglottitis now rare in U.S., and more likely to occur in adults (waning Immunity)
- Haemophilus Influenzae Pneumonia
- Non-Encapsulated Strains (Non-Typeable Haemophilus Influenzae, NTHi)
- Non-Invasive Disease (most common)
- Invasive Disease in Adults (age >65 years, lung disease, Immunocompromised status)
- Bacterial Pneumonia
- NTHi is among the top 2 causes of Bacterial Pneumonia in hospitalized patients (esp elderly)
- Bacterial Pneumonia
IV. Management: Antibiotics
-
General
- Beta-lactam resistance in Haemophilus Influenzae may approach 50% in some communities
- Empiric Antibiotics should cover Beta-Lactamase producers until culture sensitivity is returned
- Intravenous Antibiotics in Life-threatening Disease (e.g. Meningitis)
- Oral Antibiotics in Non-Life Threatening Disease
- Alternative Antibiotics (e.g. allergy)
- Levofloxacin
- Doxycycline
- Azithromycin or Clarithromycin (resistance is common)
V. Prevention
-
Haemophilus influenzae B Vaccine (Hib Vaccine)
- Released in 1987, Hib Vaccine has reduced invasive Hib associated disease by 99%
VI. Resources
VII. References
- Gladwin, Trattler and Mahan (2014) Clinical Microbiology, Medmaster, Fl, p. 96-7
- Sanford Guide, accessed 2/3/2025
- Oliver (2023) Clin Infect Dis 76(11):1889-95 +PMID: 36722332 [PubMed]