Measles surveillance in Canada: Trends for 2013

Abstract

Objective: The objective of this report is to describe measles activity in Canada during 2013, in order to support the documentation and maintenance of measles elimination status.

Methods: A descriptive analysis of measles counts and incidence by age group, immunization history, hospitalization and province/territory, as well as a summary of 2013 outbreaks, was conducted using enhanced measles data captured through the Canadian Measles and Rubella Surveillance System. Genotype information and phylogenetic analysis for 2013 were summarized.

Results: In 2013, 83 confirmed measles cases were reported in seven provinces/territories for an incidence rate of 2.4 per 1,000,000 population. Incidence was highest in the youngest age groups (< 1 year, 1 to 4 years). Burden of disease was highest in the youngest age groups and children 10 to 14 years. Three-quarters of cases had been inadequately immunized, and 10% were hospitalized. There were nine measles outbreaks reported in 2013, one of which consisted of 42 cases in a non-immunizing community in Alberta.

Discussion: 2013 saw the fifth highest number of reported measles cases since 1998. While we continue to face challenges related to importation and heterogeneous immunization coverage, in 2013 Canada met or partially met all four criteria outlined by the Pan American Health Organization for measles elimination.

Figure 1. Number of reported measles cases by epidemiological week of rash onset and reporting province or territory, Canada, 2013

Figure 2. Phylogenetic tree of measles N-450 sequences detected in Canada in 2013 (n = 50)

Each entry represents a sequence from an individual measles case. Phylogenetic trees demonstrate the relatedness of genetic sequences. Sequences on the same vertical line are identical. The length of horizontal lines separating sequences or branches of sequences is proportional to the number of differences (measured in single nucleotides) between the sequences (scale shown at the bottom left). WHO reference sequences (10) are shown in bold, italic font. Relevant sequence variants are shown in italics. These are identified within the WHO measles sequence database, MeaNS (accessible at http://www.who-measles.org/Public/Web_Front/sequence.php), and represent prevalent sequences within the database (10) Canadian sequences are shown in regular font and are identified by their WHO name, which indicates province and week of rash onset or specimen collection. Cases of imported virus are identified with “ex:< 3 letter country code>.” Outbreaks are represented by colour fonts: sequences with the same colour, within the same genotype, are from the same outbreak.

Figure 3

Phylogenetic tree of measles H gene sequences detected in Canada in 2013 (n = 43) WHO reference sequences (10) are shown in bold, italic font. Canadian sequences are shown in regular font and are identified by their WHO name, which indicates province and week of rash onset or specimen collection. Cases of imported virus are identified with “ex:< 3 letter country code>.” Outbreaks are represented by colour fonts: sequences with the same colour, within the same genotype, are from the same outbreak.