Notifiable disease trends: acute and chronic HB report rates, 1990–2013
Between 1990–2013, the overall incidence of acute-HB cases per 100,000 decreased by 97 % from 6.5 to 0.2 (p<0.0001), (Fig. 1). In children ≤9 yoa, the acute-HB incidence decreased from 0.6 in 1990 to no cases since 2010 (p < 0.0001). In those 10–19 yoa, the incidence of 3.2 in 1990 also decreased to zero since 2007 (p < 0.0001). Finally, in adults 20–29 yoa, the incidence of 15 per 100,000 in 1990, formerly the highest of all age groups, also fell to zero in 2013 (p < 0.0001).
During the same period, the overall rate of newly-reported chronic-HB cases per 100,000 decreased by 66 % from 17.7 to 6.1 (p < 0.0001), with a reduction of 92 % (2.4 to 0.2;p < 0.001) in children ≤ 9 yoa and 83 % (7.2 to 1.2;p = 0.003) in those 10–19 yoa. The rate of unspecified case reports showed an initial downward then upward trend during the study period. However, rates were low and stable throughout in children ≤ 9 yoa (0.3 vs. 0.2;p = 0.70) and 10–19 yoa (1.6 vs. 1.5;p = 0.45) old (Fig. 1). The upward trend in unspecified case reports since 2004 was among adults ≥20 yoa and primarily 30–39 yoa (Fig. 1).
Acute-HB case reports – potential for prevention through infant immunization
Among children ≤9 yoa, there were 9 acute-HB case reports during the 2005–2013 period, all before 2010 and of whom 8 would not have been preventable by routine universal infant immunization. Five children had been adopted from HB-endemic countries and were already infected upon arrival in Canada. Three children were born in Quebec from HBsAg-positive mothers: two had received immunoglobulin at birth and 3 or 4 doses of vaccine according to the recommended schedule. The parents of the third child refused prenatal screening; the mother was identified to be HBsAg-positive 2 months post-delivery and the child was diagnosed with HB a few months after birth. The final acute HB case was born in another Canadian province and was diagnosed at preschool age. The mother was born in a highly-endemic country but her HBsAg status and the child’s age upon arrival in Quebec were unknown. Assuming that this latter case was preventable, then over and above the existing program, an infant immunization program could have spared 0.0249 acute-HB cases per 100,000 person-years (CI:0.0248-0.0251) in children ≤9 yoa between 2005 and 2009 and none between 2010 and 2013.
There were two acute-HB cases reported in individuals 10–19 yoa between 2005 and 2013; both occurred before 2008. The first was an unvaccinated homosexual boy born in Quebec; the second was a drug user with no information on country of birth or vaccination status. In addition to school-based HB vaccine-eligibility, these two individuals would have been eligible for immunization on the basis of high-risk behaviours but assuming infant immunization may have spared their infection, this would correspond to an additional preventable rate of 0.0654/100,000 person-years (CI:0.0651-0.0657) between 2005 and 2007 in that age group, and none between 2008 and 2013.
Overall, in addition to the existing program, an infant immunization program could have prevented 0.0335 (95 % CI: 0.0334-0.0336) acute-HB cases per 100,000 person-years between 2005 and 2009 in people 0–19 years old.
Chronic-HB and unspecified cases – risk factors
With no acute-HB case reported in children ≤9 yoa since 2010, we limited the analysis of risk factors among chronic cases to the period spanning 2005–2009.
Among the 38 chronic-HB cases reported in children ≤9 yoa, 34 (89 %) were born outside Quebec, three were born in Quebec and one lacked place-of-birth information. The three Quebec-born children had known HBsAg-positive mothers, received adequate vaccination and immunoglobulin at birth and were not preventable. Among the 34 (89 %) immigrant cases, 13 were already infected upon arrival in Canada or diagnosed with chronic-HB during the first 12 months thereafter; 9 had unknown HBsAg status at arrival but were born from a known HBsAg-positive mother; and one was fully vaccinated before arrival. For the other 11 cases there was insufficient information to explain when and how they became infected.
In the 10–19 yoa group, there were 118 chronic-HB cases reported between 2005 and 2009. Of these, 9 cases were born in Quebec and 109 cases (92 %) were born outside Quebec (n = 84) or with unknown place of birth (n = 25). Among individuals born in Quebec, 2 were born to HBsAg-positive mothers, 2 had HBsAg carriers among their family members, 2 reported unsafe sex, 2 had parents born in an endemic country with unknown HB status and one did not report any risk factor. The two cases born to HBsAg-positive mothers were probably infected at birth and would likely not have been prevented by an infant program starting at 2 months of age. Among the other 109 chronic-HB cases, 80 (68 %) were born in a high-endemicity country, 2 had HBsAg carriers among their family members, 2 were born to an HBsAg-positive mother, and 1 reported sexual aggression as a potential cause of infection.
In addition, there were 15 case reports in people 10–19 yoa with unspecified acute or chronic HB status, 5 of whom were born in a high-endemicity country and another whose parents were born in an endemic country. For the other 9 unspecified cases, there was no information on country of birth or other risk factors.
Globally, among the 182 cases reported in those ≤19 yoa, 133 cases were born outside Quebec, 122 (91 %, CI:87 %-96 %) of whom were born in an endemic country.