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Haemophilus influenzae 

Haemophilus influenzae

Chapter:
Haemophilus influenzae
Author(s):

Derrick W. Crook

DOI:
10.1093/med/9780199204854.003.070612_update_001

Update:

Update on epidemiology of H. influenzae infection including risk factors for infection and impact of Hib vaccination.

Update on nontypeable H. influenzae (NTHi).

Emergence of Β‎-lactamase negative (BLNAR) H. influenzae.

Updated on 31 May 2012. The previous version of this content can be found here.
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date: 28 March 2017

Haemophilus influenzae is a Gram-negative bacillus that is an exclusively human pathogen. There are six capsular serotypes (a–f), of which type b (Hib) is a major cause of childhood infectious disease. Transmission occurs by close bodily contact, the main source being other children, and is usually followed by nasopharyngeal carriage, following which susceptible people may develop disease.

Clinical features—in infants Hib causes symptoms ranging from a mild nonspecific febrile illness (occult bacteraemia) to fully blown sepsis with meningitis, epiglottitis, pneumonia, septic arthritis, and cellulitis. Nontypeable H. influenzae (NTHi) are common nasopharyngeal commensals and may cause otitis media and conjunctivitis in children, and exacerbations of chronic bronchitis, sinusitis, and pneumonia in adults. H. parainfluenzae, H. aphrophilus, H. paraphrophilus, and H. segnis are rare causes of infective endocarditis and other sepsis.

Diagnosis and treatment—Gram staining of cerebrospinal, synovial, or pleural fluid is a key investigation, but definitive diagnosis requires culture or detection of H. influenzae DNA by polymerase chain reaction (PCR) methods. Aside from supportive care, treatment requires (1) appropriate antibiotics—resistance is an increasing problem: the agent of choice for invasive Hib disease is a third-generation cephalosporin with good cerebrospinal fluid penetration (e.g. ceftriaxone or cefotaxime); chloramphenicol with or without ampicillin remains effective in some developing countries. (2) corticosteroids—except in children in low-income countries, these reduce mortality, severe hearing loss, and neurological sequelae of Hib meningitis. Antibiotic treatment of noncapsulate H. Influenzae otitis media, sinusitis, and chronic bronchitis is widely practised but largely unsupported by evidence.

Prevention—conjugate Hib vaccines are given as part of the routine infant immunisation schedule and have virtually eliminated invasive Hib disease from North America, Europe and some other countries.

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