Normal flora in upper respiratory tract.
May also colonise conjunctiva and genital tract.
Most common strains are Hib and the unencapsulated.
Human is the only natural host
H. influenzae infection has dropped since vaccination.
Capsule -> important virulence factor.
Most serious infection is related with capsule type b (Hib)
Transmission - by respiratory droplet
IgA protease - facilitate colonisation
More often by unencapsulated
More often by Hib
H. aegyptius (aka H. influenzae biotype, or Koch-Weeks bacillus)
-> can cause outbreaks of purulent conjunctivitis
-> can also cause Brazilian purpuric fever
H. ducreyi
-> cause chancroid (soft chancre) (STD)
* painful genital lesions + inguinal lymphadenopathy
-> formation of bubo (swollen lymph node) -> suppuration
Pleomorphic
May have capsule (6 types) or uncapsulated.
Cultured on chocolate agar (growth requires X factor (hemin) and V factor (NAD+))
Capsular type can be tested by Quellung reaction or by immunofluorescent staining.
Need to test sensitivity
First line for non-life threatening: Ampicillin+sulbactam
First line for life-threatening: cefotaxime, ceftriaxone
Second line: trimethoprim+sulfamethoxazole
Azithromycin for H. ducreyi infection
Given for children <2 y.o.
Rifampicin given for prophylaxis in close contacts
Things to revise/add later:
Bibliography:
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Created | 20040402 |