Haemophilus influenzae is a small, nonmotile, non-spore-forming bacterium, and a strict parasite of humans found principally in the upper respiratory tract. The production of
capsule is of major significance to clinicians since it is an important
virulence factor. We described six antigenically distinct capsular types, designated a-f. Spread from one individual to another occurs by airborne droplets or by direct contagion with secretions. Haemophilus influenzae produces at least two factors that inhibit the ciliary activity of human epithelial cells in vitro. One of this has been shown to be
lipopolysaccharide and the other factor is of low molecular weight, most likely a heat-stable
glycopeptide. Type b strains are distinguished by the production of capsular
polysaccharide composed of repeating units of ribosyl-
ribitol phosphate, account for greater than 95 percent of systemic
infections in children. Two contrasting patterns of Haemophilus influenzae disease can be identified. The first and the most serious in its consequences is invasive
infection such as
meningitis,
septic arthritis,
epiglottitis, and
cellulitis in which
bacteremia is a prominent feature; these
infections are usually caused by type b strains and occur in young children. The second category includes less serious but numerically more common
infections, that occur as a result of contiguous spread of Haemophilus influenzae within the respiratory tract; e.g.
otitis media,
sinusitis. These latter
infections are usually, but not invariably, caused by unencapsulated strains. A provisional diagnosis of
meningitis,
epiglottitis, facial
cellulitis, or
septic arthritis will usually be prompted by the history and clinical findings. Confirmation requires microbiologic studies. Cultures of blood, CSF and other normally sterile fluids are diagnostic and therefore under the appropriate circumstances mandatory. Whenever feasible, specimens obtained for culture should also the gram-strained. Detection of capsular
antigen in serum, CSF or concentrated urine using immunoelectrophoresis,
latex agglutination or
enzyme linked
immunosorbent assay may be diagnosed and can be found in up to 90 percent of culture proved cases of
meningitis. Without treatment,
infection due to Haemophilus influenzae can be rapidly fatal, particularly by
meningitis and
epiglottitis. There is currently a trend to use certain parenteral
third generation cephalosporins as initial
therapy when lifethreatening
Haemophilus influenzae infection is known or suspected in children beyond the neonatal period, commonly used agents included
cefotaxime or
ceftriaxone.
Antibiotic therapy is only one facet of the management of the child with
Haemophilus influenzae infection, and critical attention must also be given to supportive
therapy. In the ambulatory setting,
ampicillin or
amoxicillin for 10 days is often satisfactory for the less severe
Haemophilus influenzae infections.
Cephalosporins are often chosen for treatment of adults, with
pneumonia when Haemophilus influenzae is documented.