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Section 3. Summaries of Infectious Diseases
Haemophilus influenzae Infections
Clinical Manifestations
Etiology
Epidemiology
Diagnostic Tests
Treatment
Isolation of the Hospitalized Patient
Control Measures (For Invasive Hib Disease)
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.
Nontypeable strains more commonly cause infections of the respiratory
tract (eg, conjunctivitis, otitis media, sinusitis, pneumonia)
and, less often, bacteremia, meningitis, chorioamnionitis, and
neonatal septicemia.
ETIOLOGY: Haemophilus 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 nontypeable.
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 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 nontypeable
strains, which are recovered from the nasopharynx of 40% to
80% of children. Nasopharyngeal colonization by type b organisms
is rare, occurring in 2% to 5% of children in the prevaccine
era and even fewer children after widespread immunization. Colonization
by strains expressing nontype b capsules also is uncommon. The
exact period of communicability is unknown.
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 meningitis and most other invasive Hib infections occurred between 6 and 18 months of age. In contrast, . . . [Go to Full Text]
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