| Clinical
Features |
Before the availability of the Haemophilus
influenzae serotype b (Hib) conjugate vaccine in the United
States and other industrialized countries, more than one-half
of Hib cases presented as meningitis with fever, headache,
and stiff neck. The remainder presented as cellulitis, arthritis,
or sepsis. In developing countries, Hib is still a leading
cause of bacterial pneumonia deaths in children. |
| Etiologic
Agent |
Haemophilus influenzae serotype
b. |
| Incidence |
During 1980-1990, incidence was
40-100/100,000 children < 5 years old in the United States.
Due to routine use of the Hib conjugate vaccine since 1990,
the incidence of invasive Hib disease has decreased to 1.3/100,000
children. However, Hib remains a major cause of lower respiratory
tract infections in infants and children in developing countries
where vaccine is not widely used. |
| Sequelae |
3%-6% of cases are fatal; up to
20% of surviving patients have permanent hearing loss or other
long-term sequelae. |
| Transmission |
Direct contact with respiratory
droplets from nasopharyngeal carrier or case patient. |
| Risk
Groups |
Infants and young children, household
contacts, and day-care classmates. |
| Surveillance |
National surveillance is conducted
through NETSS. Active laboratory-based surveillance is conducted
in Emerging Infections Program sites and other areas of the
United States. |
| Trends |
Since licensure of conjugate vaccines
for infants (1990) and children (1987), rates of disease among
children <5 years old have declined by more than 95% in
the United States, while rates for adults have remained stable.
However, rates of disease among Alaskan natives remain higher
than elsewhere in the United States. |
| Challenges |
Elimination of persistent Hib disease
in the United States. Currently available conjugate vaccines
differ in immuno-genicity in very young children and possibly
in duration of antibody persistence, raising questions about
long-term efficacy (>5 years), optimal use, and schedules.
Monitoring the possible emergence of disease due to other
serotypes. Problems with serotyping of H. influenzae in
state health departments. Development of rapid molecular assays
for detection and molecular subtyping of all Hi strains. The
cost of Hib conjugate vaccines has limited their use in developing
countries even though Hib is a major cause of morbidity and
mortality. |
| Opportunities |
Evaluating the characteristics
of Hib vaccines associated with prevention of carriage and
invasive disease will facilitate application of this technology
to development of conjugate vaccines for other organisms with
polysaccharide capsules (such as the meningococcus, pneumococcus,
and group B streptococcus). Further evaluation of herd immunity
effects may lead to insight into vaccination strategies that
optimize protection against invasive disease and transmission
of Hib organisms. |
|
December 2003
|
