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Current epidemiology and trends in invasive Haemophilus influenzae disease--United States, 1989-2008.

BACKGROUND
With the introduction of Haemophilus influenzae serotype b (Hib) conjugate vaccines, there has been a dramatic reduction of Hib disease in young children and the epidemiological trends of invasive H. influenzae have shifted.


METHODS
Data were collected from active surveillance for invasive H. influenzae disease conducted through Active Bacterial Core surveillance sites during 1989-2008.


RESULTS
During 1999-2008, the estimated mean annual incidence of H. influenzae infection was 1.62 cases per 100 000 population; 15.3% of cases were fatal. Incidence was higher among adults aged ≥65 years, compared with other age groups. The largest burden of disease among children aged <5 years was in infants aged <1 year; many of these cases occurred during the first month of life in preterm or low-birth weight infants. An estimated 10% of the total burden of disease among children aged <5 years occurred in American Indian and Alaska Native children. During 1989-2008, 7559 cases of H. influenzae disease were reported from Active Bacterial Core surveillance sites. Small increases in the incidence of serotypes a, e, and f were observed during 1989-2008. The largest of these increases was in serotype f and was primarily among adults aged ≥18 years.


CONCLUSIONS
Since the introduction of Hib conjugate vaccines, the incidence of invasive disease caused by H. influenzae in the United States has decreased dramatically; however, a considerable burden of non-Hib disease is still present in the oldest and youngest age groups. There is no evidence of substantial replacement disease with non-b serotypes in young children in the United States.