METHODS: Data were collected from active population- and laboratory-based surveillance for invasive H. influenzae disease conducted through Active Bacterial Core surveillance (ABCs) sites during 2009–2014. Isolates were serotyped via slide agglutination and real-time PCR. Case-fatality rates (CFR) were calculated using the proportion of cases with known outcomes as the denominator. Incidence rates per 100,000 population were determined using US Census data for ABCs sites; projected nationwide estimates were standardized for race and age.
RESULTS: During the surveillance period, ABCs sites reported 4,124 cases of invasive H. influenzae disease among all ages, resulting in an estimated national annual incidence of 1.9 cases per 100,000 population. Incidence was highest among children aged <5 years (6.5) and adults aged ≥65 years (6.4). The largest burden of disease among children aged <5 years was in infants aged <1 year (incidence: 8.8). Nearly half (47%) of disease among infants aged <1 year occurred during the first month of life, 71% of which occurred in preterm or low-birth weight infants. Among children aged <5 years, disease burden was substantially higher in American Indian and Alaska Natives (AI/AN) (incidence: 43.4) than in all other races (incidence: 5.8). The most common clinical syndromes were bacteremic pneumonia (62%) and bacteremia (26%); 7% had meningitis. Overall, 14% of cases were fatal; CFR was highest among adults aged ≥65 years (20%). Incidence and CFR were highest for nontypeable H. influenzae (incidence: 1.3; CFR: 16%), as compared to non-b encapsulated serotypes (incidence: 0.6; CFR: 10%) and Hib (incidence: 0.04; CFR: 4%). Only 1.7% of invasive H. influenzae disease was due to Hib. Serotype f caused the majority (63%) of non-b encapsulated serotypes, with 20% due to serotype a, 17% serotype e, and 0.3% serotype d.
CONCLUSIONS: A considerable burden of invasive H. influenzae disease still affects the oldest and youngest age groups, particularly AI/AN children. Nontypeable H. influenzae currently causes the highest morbidity and mortality.