Learning Objectives for this Presentation:
By the end of the presentation participants will be able to: Describe changes in the epidemiology of Haemophilus influenzae type B in California.

Background:
Historically, Haemophilus influenzae type B (Hib) was the leading cause of invasive bacterial disease among young children. Although immunization of infants beginning in 1991 resulted in a significant decline in incidence, California continues to report an average of 3 cases per year among children <5 years of age.

Objectives:
To compare the epidemiologic characteristics of reported Hib cases <5 years of age during 1990-2005.

Methods:
Hib case investigation data from 1990-2005 were analyzed. California Department of Finance population estimates were used to calculate incidence rates.

Results:
Between 1990 and 2005, Hib incidence in children < 5 years of age decreased 99.8%; from 16.99 to 0.04 per 100,000.

In 1990, incidence was highest among blacks, Hispanics and Native Americans (34.73, 20.46 and 13.10 per 100,000 respectively) and lowest among whites and Asians (10.99 and 4.73 per 100,000). During 2000-2005, average annual incidence was highest among Hispanics and Asians (0.16 and 0.14 per 100,000) and lowest among whites, blacks and Native Americans (0.04, 0.00 and 0.00 per 100,000).

In 1990, of 426 Hib patients, 11 (2.6 %) were aged <2 months (underage for vaccination). Of the 407 cases aged ≥2 months, 13 (3.2%) had received ≥ 1 dose of vaccine. During 2000-2005, of 18 Hib patients, 3 (16.7%) were aged <2 months. Of the 15 children who were aged ≥2 months, 12 (66.7%) had received ≥ 1 dose of vaccine.


Conclusions:
Incidence among children aged <5 years has dropped significantly since the introduction of Hib vaccine. However, complete elimination of Hib in California will require improved age-appropriate vaccination given that 33% of the cases between 2000 and 2005 aged ≥ 2 months of age were unvaccinated.