Haemophilus

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Haemophilus

A genus of gram-negative, pleomorphic bacteria that are facultative anaerobes and are nonmotile and non-spore-forming.

Haemophilus influenzae was the first of the species to be isolated and is considered the type species. It was originally recovered during the influenza pandemic of 1889 and for a time was believed to be the causative agent of influenza; thus it was called the influenza bacillus. However, when this fallacy became apparent, the organism was renamed, still reflecting the historical association with influenza.

Haemophilus species are distinguished by a number of criteria. Strains of H. influenzae can be separated into encapsulated and nonencapsulated forms. Encapsulated strains express one of six biochemically and antigenically distinct capsular polysaccharides that are designated serotypes a through f. Nonencapsulated strains are referred to as nontypable. See Influenza, Meningitis

Haemophilus influenzae is a human-specific pathogen that inhabits the upper respiratory tract and is acquired by exposure to airborne droplets or contact with respiratory secretions. Nontypable strains can be isolated from the nasopharynx of up to 80% of normal children and adults at any given time, usually in association with asymptomatic colonization. Overall, these organisms are the leading cause of exacerbations of chronic bronchitis, and the second most common etiology of acute otitis media and sinusitis. On occasion, nontypable H. influenzae causes invasive disease such as meningitis, septicemia, endocarditis, epiglottitis, or septic arthritis. Invasive disease occurs most often in neonates and in patients with underlying immunodeficiency, especially when abnormalities in humoral immunity are present.

Encapsulated strains of H. influenzae are present in the nasopharynx of only 2–5% of children and an even smaller percentage of adults. Historically, H. influenzae type b strains were the primary cause of childhood bacterial meningitis and a majority of other bacteremic diseases in children. However, in recent years the incidence of disease due to H. influenzae type b has plummeted in the United States and other developed countries, reflecting the routine use of H. influenzae conjugate vaccines. These vaccines provide effective protection against disease due to H. influenzae type b but fail to protect against non-type b strains.

Haemophilus aphrophilus, H. haemolyticus, H. parahaemolyticus, H. parainfluenzae, and H. segnis are members of the normal flora in the human oral cavity and oropharynx and have low pathogenic potential. Among these species, H. parainfluenzae is the most common pathogen and has been reported in association with a variety of diseases.

Strains of H. influenzae are increasingly resistant to a wide variety of antibiotics. Accordingly, an extended-spectrum cephalosporin is generally recommended for empiric treatment of serious disease. See Antibiotic, Drug resistance, Medical bacteriology

Haemophilus

[hē′mä·fə·ləs]
(microbiology)
A genus of gram-negative coccobacilli or rod-shaped bacteria of uncertain affiliation; cells may form threads and filaments and are aerobic or facultatively anaerobic; strictly blood parasites.
References in periodicals archive ?
Haemophilus influenzae Type B Infections - Therapeutics under Investigation by Universities/Institutes 12
Variability in the functional activity of vaccine-induced antibody to Haemophilus influenzae type b. Pediatr Res 1990; 27(4 Pt 1):358-64.
Kristensen, "Haemophilus influenzae type b. Epidemiology of invasive diseases, antimicrobial resistance of clinical isolates, and response to a conjugate vaccine in selected risk groups," Danish Medical Bulletin, vol.
Elimination of Haemophilus influenzae type b (Hib) disease from The Gambia after the introduction of routine immunisation with a Hib conjugate vaccine: a prospective study.
Waterhouse-Friderichsen syndrome caused by Haemophilus influenzae type B in an adult.
Effectiveness of Haemophilus influenzae type b (Hib) conjugate vaccine introduction into routine childhood immunization in Kenya.
A functional tonB gene is required for both utilization of heme and virulence expression by Haemophilus influenzae type B. Infect Immun.
Dr Richard Roberts, who leads the immunisation programme across Wales, said the fears raised about MMR had a knock-on effect on confidence in other vaccines; and immunisation rates at age one for illnesses like diphtheria, tetanus, polio, meningitis C and haemophilus influenzae type B fell because of concerns about MMR.
"Decline of Haemophilus influenzae type b disease in a region of high risk; impact of passive and active immunization." Pediatr Infect Dis J.
Protects against: Haemophilus influenzae type b, an infection that can seriously harm a child's brain, blood, bones, throat, and the area around the heart.

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