Epidemiology ofHaemophilus influenzaeSerotype a, North American Arctic, 2000–2005

Michael G Bruce,Carolynn Debyle,Tom Hennessy,Andre Corriveau,Alan J Parkinson,Bryce Larke,Carolina Palacios,Colleen Hemsley,Shelley L Deeks,Marguerite Lovgren,Cheryl Case,Raymond Tsang,Isaac Sobel,Tammy Zulz,Christine Navarro

doi:10.3201/eid1401.070822

Abstract

Before the introduction of Haemophilus influenzae type b (Hib) conjugate vaccines, rates of invasive H. influenzae disease among indigenous people of the North American Arctic were among the highest in the world. Routine vaccination reduced rates to low levels; however, serotype replacement with non-type b strains may result in a reemergence of invasive disease in children. We reviewed population-based data on invasive H. influenzae in Alaska and northern Canada from 2000-2005; 138 cases were reported. Among 88 typeable isolates, 42 (48%) were H. influenzae type a (Hia); 35 (83%) occurred in indigenous peoples. Among Hia patients, median age was 1.1 years; 62% were male; 1 adult died. Common clinical manifestations included meningitis, pneumonia, and septic arthritis. Overall annual incidence was 0.9 cases per 100,000 population. Incidence among indigenous children <2 years of age in Alaska and northern Canada was 21 and 102, respectively. Serotype a is now the most common H. influenzae serotype in the North American Arctic; the highest rates are among indigenous children.

Highlights

Haemophilus influenzae causes illnesses ranging from local respiratory infection to serious invasive disease, including meningitis, epiglottitis, septic arthritis, and septicemia [1]
Our data demonstrate that 69% of invasive H. influenzae disease in the North American Arctic is caused by non-b serotypes (Alaska 51%; northern Canada 89%) with serotype a comprising almost half of cases (Alaska 24%; northern Canada 74%)
The overall annualized incidence of H. influenzae type a (Hia) in children

Summary

Introduction

Haemophilus influenzae causes illnesses ranging from local respiratory infection to serious invasive disease, including meningitis, epiglottitis, septic arthritis, and septicemia [1]. With widespread vaccination against Hib, concern has been raised about the potential for replacement disease caused by non–type b encapsulated strains. It was suggested that reducing carriage of the vaccine type may open an ecologic niche, allowing increased colonization with non–type b strains of H. influenzae with the potential to become invasive [6,16]. Non–type b H. influenzae disease is uncommon in children; since the introduction of Hib vaccine, the relative importance of infections due to nonencapsulated and non–type b encapsulated H. influenzae has increased [3]. Numerous case reports of invasive H. influenzae disease caused by encapsulated non-b serotypes, types a, e, and f, have been published [6,10,11,18,19,20]

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