Invasive Haemophilus influenzae disease in Utah children: an 11-year population-based study in the era of conjugate vaccine.

BACKGROUND The incidence of invasive Haemophilus influenzae infection decreased dramatically since the introduction of the H. influenzae serotype b (Hib) conjugate vaccine. H. influenzae invasive disease continues to occur and cause significant morbidity and mortality in children aged <5 years. We aimed to report the epidemiology and serotypes of invasive H. influenzae disease in children from Utah in the post-Hib vaccine era. METHODS We identified all cases of invasive H. influenzae disease, defined as H. influenzae isolated from a sterile site, during the period 1998-2008 among children aged <18 years who were living in Utah. RESULTS We identified 91 cases of invasive H. influenzae disease in children. Children aged <5 years accounted for 78 cases (86%). H. influenzae serotype a (Hia) was the most common serotype (22 cases), representing 28% of all cases of invasive disease among children aged <5 years. The majority (15 cases [93%]) of Hib disease cases occurred among children aged <5 years and accounted for 18% of all cases of H. influenzae invasive disease in this age group. The mean incidence of Hia disease increased from 0.8 cases per 100,000 child-years in 1998 to 2.6 cases per 100,000 child-years in 2008. The incidence of Hib disease among children aged <5 years remained steady at 0.5 cases per 100,000 child-years. Bacteremia accounted for 61% of all cases of invasive disease. One-half (13 of 26) of cases of H. influenzae meningitis were due to Hia. CONCLUSIONS H. influenzae continues to cause invasive disease in Utah children. Hia is the primary cause of the overall increased incidence of invasive H. influenzae disease and leads to disease similar to Hib. Isolated cases of Hib disease demonstrate a continued reservoir. The success of the Hib conjugate vaccine may therefore be vulnerable to vaccine shortages and refusal of vaccination.