Invasive Haemophilus influenzae disease in Alaskan residents aged 10 yearsand 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 Alas kan children, How ever, the impact of vaccination on unimmunized Alaskan ad olescents and adults has not been studied. Objective To characterize trends in incidence of and mortality due to invas ive H influenzae disease in Alaskan residents aged 10 years and older prior to and after the introduction of a statewide Hib infant vaccination progra m. Design and Setting Population-based, descriptive correlational study conduc ted 1980-1996 in Alaska, Subjects One hundred twenty-nine individuals (31 Alaska Natives and 98 nonn ative Alaska residents) aged 10 years and older in whom H influenzae was cu ltured 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, a nd 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 dec lined from 4.2 per 100000 persons per year to 1.2 per 100000 persons per ye ar 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). Pne umonia (43%), sepsis (26%), and meningitis (16%) were the most common clini cal presentations. Alcohol/drug abuse was comorbid in 15% of patients, whil e 13% of patients were pregnant women. beta-Lactamase production occurred i n 35% of isolates and was stable throughout the surveillance. The overall c ase-fatality rate was 15%. Conclusion The overall statewide incidence of invasive H influenzae infecti ons in unimmunized persons aged 10 years and older decreased after the init iation of an infant Hib vaccine program, perhaps by decreasing Hib carriage in child reservoirs. An increase in non-serotype b strains was observed. T his trend justifies the need for continued surveillance of invasive disease caused by H influenzas.