| 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 Programme 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 optimise protection against invasive disease and transmission of Hib organisms. |
