Invasive Disease due to <i>Haemophilus influenzae</i> Type A in Children in Canada’S North: A Priority for Prevention

aemophilus influenzae type B (HiB) was the major cause of menin- gitis and a frequent cause of other invasive infections in young children until an effective vaccine became available in the early 1990s.In the prevaccine era, the estimated yearly incidence of invasive disease in the United States (US) for children <5 years of age was 40 to 100 cases per 100,000.Infection rates were highest in Aboriginal children (1).For Inuit children <5 years of age residing in the Keewatin district in Nunavut, the rate of HiB meningitis alone was 530 cases per 100,000 (2); however, HiB infection is now rare.Immunization against HiB protects against disease and also reduces carriage of this organism.After the remarkable success of the conjugate HiB vaccine in controlling HiB, there has been concern about the possibility of serotype replacement, as has been observed with pneumococcus (1,3,4).Historically, invasive infections involving H influenza serotypes other than B were sporadic and rare (5).However, in recent years, increasing rates of invasive infection due to H influenzae type A (HiA) have been reported in the Canadian north, as well as in Alaska (USA) and in Aboriginal populations in the southwestern US and Australia (1,6,7).In Alaska, where surveillance for all invasive H influenzae infections has been onging since 1983, HiA was not detected before 2002 (8).Between 2002 and 2005, rates for Indigenous children <2 years of age in northern Canada and Alaska were 101.9 and 20.9 per 100,000, respectively (3).An incidence of 87.5 per 100,000 for children <2 years of age was reported in the Canadian circumpolar region from 2000 to 2010 (6).In 2001, in the Keewatin region of Nunavut, the rate for children <5 years of age was 418.8 per 100,000 (9).Outbreaks occurred in Alaska in 2003 and 2009 to 2011 (3,8), as well as in Nunavik, northern Quebec, from 2012 to 2013 (10).Recurrent disease has been reported in three apparently healthy children who were <10 months of age at initial infection (11,12).Case fatality rates of 5.5% to 16% have been observed (6,8,9).HiA infections in the non-Aboriginal population in the US remain rare (13).In Quebec, before 2010, there were one or two cases of invasive HiA infection per year, with no cases from Nunavik.There was an average of four cases per year in Nunavik from 2010 to 2012, and 10 cases in 2013.Most cases involved young children, and presentations included meningitis, septicemia, septic arthritis and bacteremic pneumonia.Infection rates for 2010 to 2013 were 330.1 and 191.4 cases per 100,000 for children <1 year of age and one to four years of age, respectively, compared with an overall rate in Quebec of 2.0 and 0.8 for these age groups.There were two deaths in 2013, an infant six months of age and another 10 months of age (10).Children from Nunavik are transferred to the Montreal Children's Hospital (Montreal, Quebec) if they require care that cannot be provided in the north.There were no children transferred with invasive HiA disease before 2010, one in 2010, none in 2011; however, 12 were transferred from 2012 to 2013.In 2013, two cases were from the same household, with onset of illness 24 h apart.In

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