Haemophilus influenzae

Haemophilus influenzae causes diseases predominantly affecting children.

Epidemiology

Incidence – rate of disease for type B has decreased with immunizations
- WHO estimates 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
May colonize the human upper airways
- Up to 80% of healthy people carry nontypeable H. influenzae

Clinical Presentation

Otitis media, sinusitis, pharyngitis – usually children
Cellulitis – predominantly in young children
Pneumonia – particularly in the elderly, patients with chronic obstructive pulmonary disease (COPD), and patients who are immunocompromised
- 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 Testing

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

Laboratory Testing

Rapid antigen detection tests are available, but their 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
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 due to other bacterial, viral or atypical organisms
Pharyngitis – Streptococcus group A, EBV
Cellulitis – Staphylococcus aureus, Streptococcus group A
Meningitis – bacterial, viral, fungal etiologies

Tests generally appear in the order most useful for common clinical situations

Test name: Diphtheria, Tetanus, and H. Influenzae b Antibodies, IgG

ARUP #: 0050779

Methodology: Quantitative Multi-Analyte Fluorescent Detection

Use:

Determine patient response to vaccine and whether protective antibody levels have been reached

Determines IgG antibody titers to tetanus and diphtheria toxoids and H. influenzae PRP simultaneously

Follow-up:

If concentrations of IgG, IgM, and IgA range from low to normal and antibody deficiency still strongly suspected, determine IgG subclass and response to protein antigens (eg, diphtheria, tetanus toxoid, influenzae) as well as to pure polysaccharide antigens (eg, unconjugated pneumococcal vaccine)

Test name: CBC with Platelet Count & Automated Differential

ARUP #: 0040003

Methodology: Automated Cell Count with Flow Cell Differential

Use:

Evaluate for possible infectious process

Test name: Respiratory Culture (Includes Gram Stain 0060101)

ARUP #: 0060122

Methodology: Standard reference procedures for bacterial stain, aerobic culture, and identification. Sinus swabs or aspirates should be ordered as a Wound Culture (0060132).

Use:

Determine type of organism involved in pneumonia

Test name: Blood Culture

ARUP #: 0060102

Methodology: Bactec® continuous monitoring system. Standard reference procedures for identification of aerobic and anaerobic microorganisms

Use:

Identify organisms causing bacteremia

Limitations:

Testing is limited to the University of Utah Health Sciences Center only

Test name: CSF Bacterial Culture (Includes Gram Stain 0060101)

ARUP #: 0060106

Methodology: Standard reference procedures for bacterial stain, aerobic culture, and identification