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

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). Median age of case-patients was 0.7 years; 3 infants died. Incidence of Hia infection (2002–2011) among children <5 years was 5.4/100,000; 27 cases occurred in Alaska Native children (18/100,000) versus 2 cases in non-Native children (0.5/100,000) (risk ratio = 36, p<0.001). From 12/2009 to 12/2011, 15 cases of Hia disease occurred in southwestern Alaska (in children <5 years, rate = 204/100,000). Since introduction of the Hib conjugate vaccine, Hia infection has become a major invasive bacterial disease in Alaska Native children.

Classification, Identification, and Clinical Significance of Haemophilus and Aggregatibacter Species with Host Specificity for Humans

“…Routine use of the Hib vaccine has changed the epidemiology of H. influenzae, and unencapsulated H. influenzae now accounts for most invasive infections, followed by serotypes f and b (224)(225)(226)(227)(228)(229). An unexpectedly large proportion of invasive childhood infections caused by serotype a was recently reported from several Canadian provinces (205,230) and among Alaska Native children (231). There is no evidence of substantial replacement disease with non-b serotypes in young children in the United States (232) or of increases of non-b infection in Australian indigenous children (233).…”

Collaboration on a public health-driven vaccine initiative

“…Since northern Canada has a relatively high indigenous population and Hia, being similar to Hib including its epidemiology, has replaced Hib as a cause of significant burden of invasive diseases in the post-Hib vaccine era (17). This trend has also been observed in Alaska, U.S.A. (18).…”

Treatment strategies for central nervous system infections: an update

“…Serotype replacement has been seen with an increase in incidence of non-type b cases. In a statewide surveillance done in Alaska from 1983 to 2011, no H. influenzae type a disease was identified before 2002 but between 2002 and 11, 32 cases were identified while from December 2009 to December 2011, 15 cases were identified [18].…”