[Clinical manifestations, diagnosis and treatment of Haemophilus influenzae infection]

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.