Invasive Haemophilus influenzae disease in Alaskan residents aged 10 years and older before and after infant vaccination programs

Context The introduction of Haemophilus influenzae type b (Hib) vaccination of children has led to a decline in incidence of Hib disease in young Alaskan children, How ever, the impact of vaccination on unimmunized Alaskan adolescents and adults has not been studied. Objective To characterize trends in incidence of and mortality due to invasive H influenzae disease in Alaskan residents aged 10 years and older prior to and after the introduction of a statewide Hib infant vaccination program. Design and Setting Population-based, descriptive correlational study conducted 1980-1996 in Alaska, Subjects One hundred twenty-nine individuals (31 Alaska Natives and 98 nonnative Alaska residents) aged 10 years and older in whom H influenzae was cultured from a normally sterile site. Main Outcome Measures Incidence of H influenzae infection before (1980-1990) vs after (1991-1996) vaccination program initiation; serotype, biotype, and p-lactamase production of isolates. Results The overall annual incidence of invasive H influenzae in those aged 10 years and older declined 33%, from 2.1 per 100000 persons per year to 1.4 per 100000 persons per year (P=.03) after initiation of statewide infant Hib vaccination programs in 1991. This reduction appeared to be the result of a decrease in serotype b disease (82%; P<.001). Infection with other H influenzae serotypes and nontypeable strains increased from 0.5 per 100000 persons per year to 1.1 per 100000 persons per year (P =.01). Incidence declined from 4.2 per 100000 persons per year to 1.2 per 100000 persons per year in Alaska Natives (P=.005) and from 1.7 per 100000 persons per year to 1.4 per 100000 persons per year in non native Alaska residents (P =.37). Pneumonia (43%), sepsis (26%), and meningitis (16%) were the most common clinical presentations. Alcohol/drug abuse was comorbid in 15% of patients, while 13% of patients were pregnant women. beta-Lactamase production occurred in 35% of isolates and was stable throughout the surveillance. The overall case-fatality rate was 15%. Conclusion The overall statewide incidence of invasive H influenzae infections in unimmunized persons aged 10 years and older decreased after the initiation of an infant Hib vaccine program, perhaps by decreasing Hib carriage in child reservoirs. An increase in non-serotype b strains was observed. This trend justifies the need for continued surveillance of invasive disease caused by H influenzas.