Haemophilus influenzae Serotype a Invasive Disease, Alaska, USA, 1983–2011

Michael G. Bruce

, Tammy Zulz, Carolynn DeByle, Ros Singleton, Debby Hurlburt, Dana Bruden, Karen Rudolph, Thomas Hennessy, Joseph Klejka, and Jay D. Wenger

Author affiliations: Centers for Disease Control and Prevention, Anchorage, Alaska, USA (M.G. Bruce, T. Zulz, C. DeByle, D. Hurlburt, D. Bruden, K. Rudolph, T. Hennessy, J.D. Wenger); Alaska Native Medical Center, Anchorage (R. Singleton); Yukon Kuskokwim Health Corporation, Bethel, Alaska (J. Klejka)

Abstract

Before introduction of Haemophilus influenzae type b (Hib) vaccines, rates of Hib disease in Alaska’s indigenous people were among the highest in the world. Vaccination reduced rates dramatically; however, invasive H. influenzae type a (Hia) disease has emerged. Cases of invasive disease were identified through Alaska statewide surveillance during1983–2011. Of 866 isolates analyzed for serotype, 32 (4%) were Hia. No Hia disease was identified before 2002; 32 cases occurred during 2002–2011 (p<0 .001="" 0.7="" 12="" 15="" 27="" 2="" 3="" 5.4="" a="" age="" alaska="" among="" bacterial="" become="" case-patients="" cases="" children.="" children="" conjugate="" died.="" disease="" from="" has="" hia="" hib="" in="" incidence="" infants="" infection="" introduction="" invasive="" major="" median="" native="" non-native="" occurred="" of="" p="" rate="204/100,000)." ratio="36," risk="" since="" southwestern="" the="" to="" vaccine="" versus="" was="" years="">

Haemophilus influenzae is a bacterial pathogen that can cause serious invasive disease. The organism is classified by the presence of a capsular polysaccharide (6 STs, a-f) or its absence (nonencapsulated or nontypeable strains). In Alaska, before introduction of H. influenzae serotype b (Hib) vaccine, rates of invasive Hib disease among Alaska Native people were among the highest in the world (1,2). Disease caused by Hib was reduced significantly after the 1991 introduction of the Hib conjugate vaccine, polyribosylribitol phosphate outer membrane protein (PRP-OMP) (3); however, this vaccine does not provide protection against the other capsular or nontypeable strains (4). H. influenzae serotype a (Hia), in particular, has been reported as the cause of serious disease in young children (5–7). We previously described invasive Hia disease in the North American Arctic (Northern Canada and Alaska) from 2000 through 2005 (8) and reported an outbreak of 5 episodes of invasive Hia disease in 3 children during 2003 in southwestern Alaska (9). Sporadic cases were reported from 2005 through 2009. In this report, we describe an outbreak of 15 cases of invasive Hia disease that occurred from December 2009 through December 2011 in neighboring areas and review the microbiology and epidemiology of Hia disease in Alaska from 1983 to 2011.