Organism: Haemophilus influenzae Flashcards
Explain the epidemiology of capsulated strain
Severe disease (type B strain)
- young children in countries that don’t include Hib vaccine in infant schedule
- Hyposplenism/ asplenism
- Congenital/ acquired immunodeficiencies (HIV CD4 T cell, complement deficiency
Give an overview of non-capsulated strain
Respiratory and mucosal infections
- acute exacerbation of chronic bronchitis
- otitis media/ sinusitis/ pneumonia
What is the structure/features of H. influenzae?
- H. influenzae is a human only organism 🡪 colonise mucosal surfaces
- found in the nasopharynx of healthy adults and children
- 5% carry capsulated strains in the nasopharynx
- 25-80% carry non-capsulated strains in the nasopharynx
What are the virulence factors of capsulated influenza?
Antimicrobial resistance
Lipooligosaccharide (LOS)- endotoxin
Outer membrane proteins
Pili/ fimbriae (attachment)
Anti-phagocytic polysaccharide capsule (PRP = polyribosylribitol phosphate)
Resistant to phagocytosis by PMNs in absence of specific anti-capsular antibody
Reduces organism’s susceptibility to bactericidal effect of serum
What are the virulence factors of non-capsulated(nontypeable)?
Antimicrobial resistance
LOS
IgA protease activity (inactive IgA in nasopharynx)
Fimbriae 🡪 attaches to pharyngeal cells
Opacity associated protein (attachment to pharyngeal cells)
Why should one take steroids before antibiotics in treatment?
To limit inflammatory response to dead bacteria’s antigen)
Give the pathogenesis of capsulated strain.
Portal- colonization of oropharynx
Attachment- fimbriae/pili
Attachment of OMPs (outer membrane proteins)
Evasion- capsule critical virulence factor that facilitates invasion + hematogenous dissemination
Damage- capsule (evades phagocytosis)
Spread- inhalation of respiratory droplets/ direct contact with respiratory secretions
What is the pathogenesis of non-capsulated strain (otitis media of children)?
Colonise patients with chronic pulmonary disease such as COPD and CF.
- ciliated columnar epithelium damaged by air pollutants
- damaged cilia = pooling of mucus
- biofilm formation
- predisposes to invasion by bacteria
(may precipitate infection when preceding/coincidens viral infection)
What are the clinical features of type B capsulated?
-respiratory tract infections in early childhood (acute epiglottitis, pneumonia)
- meningitis (sequelae: deafness, seizures, intellectual impairment)
- septicemia (often with meningitis)
- septic arthritis
- cellulitis
VACCINE PREVENTABLE
What are the clinical features of type B non capsulated?
-recurrent sinusitis
- acute/chronic bronchitis
- acute/chronic otitis media
- community acquired pneumonia
less common: invasive infection
State the laboratory features of H. influenza
Pleomorphic Gram negative bacilli/coccobacilli Stain faintly Facultative anaerobic -Maximal growth in 5% CO2 -Fastidious
What are the growth characteristics of H. influenzae?
-Require growth supplements, typically present in blood
-Grow best in environment with CO2
-H. influenzae requires 2 growth factors to grow: X and V
Both found in chocolate agar*
X is haematin
V is NAD (nicotinamide adenine dinucleotide)
-Visible colonies will typically be seen after overnight incubation
* chocolate agar with 5% CO2
Describe the lab diagnosis of H. influenzae
Systemic Infection
Epiglottitis, Bloodstream Infection, cellulitis, septic arthritis
Blood cultures
Joint fluid (septic arthritis)
Aspirate from area of cellulitis
Swab for culture & antibiotic susceptibility where appropriate
Why is taking of laryngeal or epiglottic swabs is potentially dangerous for the very young?
it may precipitate complete airway obstruction - contraindicated
Describe the lab diagnosis of suspected meningitis
Blood for culture & PCR
Cerebrospinal fluid for microscopy, culture & PCR
