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Section 3. Summaries of Infectious Diseases
Haemophilus influenzae Infections
Clinical ManifestationsEtiology
Epidemiology
Diagnostic Tests
Treatment
Isolation of the Hospitalized Patient
Control Measures (for Invasive HIB Disease)
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CLINICAL MANIFESTATIONS
Haemophilus influenzae type b (Hib) causes pneumonia, occult febrile bacteremia, meningitis, epiglottitis, septic arthritis, cellulitis, otitis media, purulent pericarditis, and other less common infections, such as endocarditis, endophthalmitis, osteomyelitis, and peritonitis. Nontype b encapsulated strains occasionally cause invasive disease similar to type b infections. Nontypable strains more commonly cause infections of the respiratory tract (eg, conjunctivitis, otitis media, sinusitis, pneumonia) and, less often, bacteremia, meningitis, chorioamnionitis, and neonatal septicemia.
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ETIOLOGY
H influenzae is a pleomorphic gram-negative coccobacillus. Encapsulated strains express 1 of 6 antigenically distinct capsular polysaccharides (a through f); nonencapsulated strains fail to react with typing antisera against capsular serotypes a through f and are designated nontypable.
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EPIDEMIOLOGY
The natural habitat of the organism is the upper respiratory tract of humans. The mode of transmission is person to person by inhalation of respiratory tract droplets or by direct contact with respiratory tract secretions. In neonates, infection is acquired intrapartum by aspiration of amniotic fluid or by contact with genital tract secretions containing the organism. Asymptomatic colonization by H influenzae is common, especially with nontypable and non-type b capsular type strains.
Before introduction of effective Hib conjugate vaccines, Hib was the most common cause of bacterial meningitis in children in the United States. The peak incidence of invasive Hib infections occurred between 6 and 18 months of age. In contrast, the peak age for epiglottitis was 2 to 4 years of age.
Unimmunized children younger than 4 years of age are at increased risk of invasive Hib disease. Factors that predispose to invasive disease include sickle cell disease, asplenia, human immunodeficiency virus (HIV) infection, certain immunodeficiency syndromes, and malignant neoplasms. Historically,
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