Recurrent invasive Haemophilus influenzae type b disease in Alaskan Natives

Alaskan Natives (Indians and Eskimos) have an extraordinary incidence of invasive Haemophilus influenzae type b (Hib) disease (500 cases/100 000 children younger than 5 years of age) and also an increased incidence of recurrent disease. However, the incidence of primary Hib disease and recurrent disease are not excessive in non-Native children in Alaska (mainly Caucasian). Twelve recurrent cases in Alaskan Natives were studied, 10 of which were detected in surveillance activities between 1971 and 1984. These recurrent episodes occurred 23 to 197 days after the initial episodes (median, 51 days); the overall rate of recurrent disease was 3.5%. The ages of the patients with recurrent disease were significantly younger than single episode cases. To determine if disease recurrence was a manifestation of the high disease incidence and earlier age at onset of disease, we calculated an expected number of recurrent cases for our study population, based on the incidence observed in children with first episodes and the period of observed follow-up. The expected number of recurrent cases was only 1.9, significantly fewer than the 10 observed, indicating that age and the high incidence of disease alone were not the only factors contributing to the recurrent disease. No other significant clinical or epidemiologic risk factors could be identified. Patients who develop recurrent invasive Hib disease may represent a subset of this population with unusual disease susceptibility.