Measles surveillance in Canada, 2019

Abstract

Background: The Public Health Agency of Canada (PHAC) has conducted enhanced measles surveillance since 1998, the year endemic measles transmission was eliminated in Canada. The objective of this annual national measles surveillance report is to provide an epidemiologic summary of measles activity reported in Canada for 2019 in order to provide evidence to support the continued verification of Canada's measles elimination status.

Methods: Measles surveillance data are housed in the Canadian Measles and Rubella Surveillance System (CMRSS) database. Descriptive analyses of demographics and risk factors were performed. Outbreak characteristics were summarized and genotypic analyses conducted. Surveillance, laboratory and vaccine coverage data for 2019 were used to assess Canada's status against the Pan American Health Organization (PAHO) essential criteria for the verification of measles elimination.

Results: In 2019, 113 measles cases were reported in Canada (crude incidence rate of 3.0 cases per 1,000,000 population). Of these cases, 42 (37%) were imported into Canada, and of the imported cases, 12 (29%) resulted in further transmission. Infants younger than one year had the highest age-specific incidence rate at 13.1 cases per 1,000,000 population. Only 29% of cases had one or more documented doses of measles-containing vaccine. One-fifth (19%) of cases were hospitalized; no deaths were reported. Genotype information was available for 100% of outbreaks reported in 2019 and 90% of non-outbreak-related measles cases; of cases with genotype information available, 27% were B3 and 73% were D8.

Conclusion: Despite meeting/partially meeting only three out of four of PAHO's essential criteria for measles elimination status, there is no evidence that endemic measles transmission has been reestablished in Canada.

Keywords: measles; measles elimination; surveillance; travel health; vaccination.

Figure 1

Number of reported measles cases (N=113), by epidemiologic week of rash onset and reporting province or territory, Canada, 2019 Abbreviations: AB, Alberta; BC, British Columbia; MB, Manitoba; NB, New Brunswick; NT, Northern Territories; ON, Ontario; QC, Québec; SK, Saskatchewan

Figure 2

Confirmed measles cases (N=113) and incidence rates (per 1,000,000 population) by age group and vaccination status, Canada, 2019

Figure 3

Maximum parsimony phylogenetic tree of measles N-450 sequences identified in Canada in 2019 (n=73) prepared using MEGA X software^a Abbreviations: ID, identifier; MeaNS, Measles Nucleotide Surveillance; WHO, World Health Organization ^a Genotype B3 sequences are shown in the orange shading and genotype D8 sequences in the blue shading. WHO genotype B3 and D8 reference sequences are included, along with their GenBank accession numbers, and can be identified with the starting text “B3” or “D8”. The four WHO-named strains that match Canadian sequences are included and begin with an asterisk (MVs/Gir Somnath.IND/42.16, MVs/Dagon Seikkan.MMR/5.18, MVi/Gombak.MYS/40.15 and MVi/Marikina City.PHL/10.18/). Canadian sequences are identified by their WHO name, which indicates province and week of rash onset (by number in the year, as assigned in accordance with WHO guidelines). Distinct sequence IDs, as identified and assigned by MeaNS, the WHO measles sequence database, are shown in brackets (4-digit number). Travel history is indicated where applicable with “ex:<country name>.” Outbreaks are represented by a single sequence. These sequences are tagged with their outbreak number in accordance with Table 1 and with the number of identical sequences identified in the outbreak in brackets. The remaining sequences (without an outbreak number listed) are from non-outbreak-related cases (n=35). The scale bar indicates number of nucleotide differences between branches

Figure 4

Number of measles cases with genotype D8, WHO-named strain MVs/Gir Somnath.IND/42.16 detected in 2018 and 2019 (n=51), by epidemiologic week of rash onset, chain of transmission status and source of exposure, Canada^a Abbreviation: WHO, World Health Organization ^a Chains of transmission (outbreak or sporadic case) are identified by colour with 2019 outbreaks numbered as per Table 4. Solid bars reflect cases with known source of exposure. Bars with diagonal stipes indicate cases with unknown source