Haemophilus influenzae

Diagnosis

Indications for Testing

• Identify etiologic agent in pneumonia, meningitis, cellulitis, septic arthritis

Laboratory Testing

• CDC - testing recommendations
• Rapid antigen detection tests are available – utility is questionable
• Otitis/sinusitis – clinical diagnosis; laboratory testing not routinely performed
• Pneumonia – CBC, chest x-ray; consider sputum culture, blood culture
  • Positive upper respiratory culture does not necessarily establish organism as pathogen due to colonization
• Cellulitis – wound culture; consider CBC, depending on clinical severity
• Meningitis – CBC, spinal tap with CSF culture and gram stain, cell count, and culture
• Immunoglobin deficiency testing
  • IgG testing for diphtheria, tetanus and H. influenzae – determine vaccination response to diagnose immunoglobulin deficiency in patients with recurrent infection
    • Need pre- and post-vaccine titers (1 month after vaccination)

Differential Diagnosis

• Community-acquired pneumonia – other bacterial, viral, or atypical organisms
• Pharyngitis – Streptococcus group A, EBV
• Cellulitis – Staphylococcus aureus, Streptococcus group A
• Meningitis – bacterial, viral, fungal etiologies

Clinical Background

Haemophilus influenzae causes diseases predominantly affecting children.

Epidemiology

• Incidence
  • WHO – 3,000,000 cases of serious disease annually
• Age – usually in children; exception is pneumonia, which affects all ages  
• Transmission – respiratory droplet or direct contact with secretions

Organism

• Small, nonmotile, nonspore-forming, fastidious gram-negative bacterium
• Requires medium containing X (porphyrins such as hemin) and V (nicotinamides such as NAD) factors for aerobic growth (eg, chocolate agar)
• Six major typable serotypes (A-F)
  • Nontypeable strains are common
• Colonizes human upper airways
  • Up to 80% of healthy people carry nontypeable H. influenzae

Clinical Presentation

• Otitis media, sinusitis, pharyngitis – usually children
• Cellulitis – predominantly young children
• Pneumonia – elderly, patients with chronic obstructive pulmonary disease (COPD), and patients who are immunocompromised
  • Common etiology of COPD exacerbations
• Meningitis – often preceded by symptoms of upper respiratory tract infection, head trauma or surgery, CSF leak, otitis or sinusitis
• Epiglottitis – usually children
• Sepsis – neonatal and maternal sepsis
• Septic arthritis – usually children <2 years
• Conjunctivitis – may occur in outbreaks, especially in daycare settings

Treatment

• Parenteral antibiotics are recommended for serious infections; oral antibiotics can be used for non-invasive disease
  • 30% of isolates produce β-lactamase

Prevention

• Vaccination

Indications for Laboratory Testing

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory

Click the plus sign to expand the table of additional tests.

Test Name and Number	Comments
Haemophilus influenzae b Antibody, IgG 0050542 Method: Quantitative Multiplex Bead Assay