Haemophilus Dr. Salma

Overview- Haemophilus Small Non-motile Gram-negative rods Transmitted via respiratory droplets, or direct contact with contaminated secretions Normal flora of the human respiratory tract and oral cavity.

Culture On chocolate agar, flat, grayish brown colonies with diameters of 1–2 mm are present after 24 hours of incubation. IsoVitaleX in media enhances growth. H influenzae does not grow on sheep blood agar except around colonies of staphylococci ("satellite phenomenon"). H haemolyticus and H parahaemolyticus are hemolytic variants of H influenzae and H parainfluenzae, respectively

Haemophilus species of clinical importance 1. H. influenzae -type b is an important human pathogen 2. H. ducreyi -sexually transmitted pathogen (chancroid) 3. Other Haemophilus are normal flora - H. parainfluenzae – pneumonia & endocarditis - H. aphrophilus – pneumonia & endocarditis - H. aegyptius – pink eye (purulent conjunctivitis) or Brazilian Purpuric Fever

Differentiation of Species Growth Factor Hemolysis X Y H. influenzae - + H. aegyptius H. ducreyi H. parainfluenzae H. aphrophilus

Pathogenesis: * H.influenzae infects Only human, there is No animal reservoir. It enters the body through the upper respiratory tract, resulting in either asymptomatic colonization or may cause infection such as sinusitis, otitis media or pneumonia. * The organism produces IgA protease that degrades the secretary IgA which facilitate its attachment to the respiratory mucosa. * Then organism enters the blood stream and reaches the meninges. * Pathogenesis involves the antiphagocytic capsule and endotoxins, no exotoxins are produced. * Most infections occur in children between the age’s 6months-6 years, with a peak of 0.5-1year, due to decrease in maternal IgG, and inability of the child to form sufficient anticapsular antibodies until the age of 2 years.

Laboratory diagnosis: Clinical findings: * Meningitis caused by H.influenzae cannot be differentiated from those caused by the other group of bacteria. * Symptoms include rapid onset of fever, headache, and stiff neck with drowsiness. * Infection may be accompanied with sinusitis and otitis media. * Unencapsulated strain can cause pneumonia in elderly adults, especially those with chronic respiratory disease. Laboratory diagnosis:  1- Organism should isolate on chocolate medium supplemented with factor X & V. 2- H.parainfluenzae does not require these two factors. 3- Further identification could be made by using Quelling reaction and fluorescent antibody technique or other immunological techniques.   Treatment: The drug of choice is ceftriaxone, because 20-30% of H.influenzae produce β lactamase.

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