| Organism: |
Haemophilus influenzae |
| Classification:
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| Family: |
Pasteurellaceae |
| Genus: |
Haemophilus |
| Specie: |
H.influenzae |
| H.
influenzae serotype b is considered most pathogenic
and virulent of the 6 capsular types |
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| Normal habitat: |
Part of normal flora of oropharynx
and nasopharynx in more than 85% of adults.
(Most oropharyngeal
isolates are non-encapsulated, however capsulated serotype
including “b” may also be found as normal
flora.)
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| Cultural characteristics: |
| (Optimal recovery
of Haemophilus depends on proper collection and
transport, as they are fastidious Media: Chocolate
Agar, Blood Agar (with staphylococcus streak
technique), Heamophilus Isolation Agar.
Growth requirements:
Aerobic, CO2 rich, 350-370
and X and V factors:
On Blood Agar (which has X-factor) Staphylococcus
aureus synthesize and secrete V factor. On Blood
Agar will grow only around staphylococcus aureus
colonies. This is called Satellitism(fig1)
More specifically, it will grow on a plate (
Mueller-Hinton agar) that has been fortified
with both X-factor (found to be hemin) and V-factor
(found to be NAD) but not either one alone(fig2)
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Colony
characteristics: On Chocolate agar; smooth bluish
grey mucoid 1-2mm entire colonies.
Biochemical reactions:
Biochemical tests are not routinely used. Six
biovars are recognized on basis of Indole, Urea,
ODC etc.
Serotyping: Multiple types of kits are available
for Serotyping especially to identify H.influenzae
type b.
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|
Immunological techniques |
Latex
particle agglutination, coagglutination and
counterimmuno -electrophoresis techniques
For rapid diagnosis of H. influenza type b,
immunological tests are used to detect capsular
antigen in CSF and other body fluid. As the
method relies on antigen rather than viable
bacteria, and result is not affected by prior
antibiotic use and it is much quicker than culture. |
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| Microscopic
Appearance: |
Small
(1 µm X 0.3 µm), pleomorphic, gram-negative
coccobacillus. It is a nonmotile, non–spore-forming.
Occasionally slender filamentous cells may be
observed |
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| Susceptibility testing: |
According
to CLSI: Haemophilus Test Medium, Direct
colony suspension of 0.5 McFarland turbidity
standard35? -37? in CO2 rich environment. |
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| 1. |
Ampicillin |
| 2. |
ß -Lactamase detection
(ß-Lactamase negative, Ampicillin Resistant
strains of H.influenza should be considered
Resistant to Co-amoxiclav,Cefaclor, Cefuroxime
despite in-vitro sensitivity) |
| 3. |
Amoxicillin-clavulonic
acid |
| 4. |
cefuroxime |
| 5. |
ceftriaxone / cefotaxime |
6. |
chloramphenicol |
7. |
Azithromycin or Clarithromycin |
8. |
ciprofloxacin (or levofloxacin or other) |
9. |
Trimethoprim/ sulphamethoxazole |
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|
As antibiotic
susceptibility and hence empirical therapy is
becoming less predictable, in vitro testing
has become increasingly important. |
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| Virulence factors: |
• |
Capsule |
|
(H.influenza
capsular type b is associated with decreased
adherence to and invasion of human cells. It
has RPR (polyribosyl-ribitol-phosphate) capsule,
which allows the organism to resist phagocytosis
and intracellular killing. |
• |
Adhesin |
• |
IgA protease |
• |
Opacity associated Protein A (OpA) |
• |
Lipopolysaccharide |
• |
Outer membrane protein
(OMPs designated P2 and P6 has generated most
interest in vaccine development |
• |
Haemocin (Its production
may contribute to the ability of H. influenza
type b to compete other strains in nasopharyngeal
colonization) |
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|
| Common infections: |
• |
Meningitis |
• |
Epiglottitis |
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Otitis media |
• |
Sinusitis |
| • |
Acute pharyngitis/laryngotracheobronchitis |
• |
Pneumonia |
• |
Bactremia |
• |
Genital tract infections |
• |
Neonatal sepsis with meningitis |
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conjunctivitis |
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| Unusual
infections: |
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Endocarditis |
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Facial and peri-orbital cellulitis |
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Endophthalmitis |
• |
Abdominal infection (peritonitis, liver
abscess) |
| • |
Hepato-biliary tract infection |
• |
Pancreatitis |
• |
Appendicitis |
• |
Osteomyelitis |
• |
Septic arthritis |
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| Drug of
choice: |
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| • |
Otitis
media and exacerbation of COPD amoxicillin/clavulanic
acid, cefaclor, cefuroxime, fluoroquinolone
and macrolide |
|
| • |
Meningitis and epiglottitis
(can be rapidly fatal without therapy)
cefotaxime/ceftriaxone is drug of choice
(treatment should be continued till patient
is afebrile and without clinical and laboratory
signs for 3 to 5 days)
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| Resistance: |
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• |
Approximately
30% of strains produce ß lactamase; ampicillin
as a sole therapy should be given only after
susceptibility of organism is determined. |
| • |
Increase in the prevalence
of plasmid-mediated ß lactamase production
as well as resistance to other drugs like chloramphenicol
Proper culture and antibiotic susceptibility
testing is Important requirement especially
in serious infection. |
| • |
At the present time, H.
influenzae isolates have not been detected that
are resistant to either third-generation cephalosporins
or fluoroquinolones.
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| Chemoprophylaxis: |
(For all who have not
received prior immunization)
In case of invasive H.influenza type b infection Rifampicin
prophylaxis is recommended for all household contacts
including adults(except pregnant women) child <2
years with incomplete immunization, and immunocompromised
child |
| Immunization: |
|
Three conjugate vaccines are
available
(RPR-T, HbOC, PRP-OMPC)
All children should be immunized with a conjugate
vaccine beginning at 2 months of age |
| • |
Primary series
(3 doses) ß2,4 and6 moths age |
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• |
A booster dose at 12 to 15 months |
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