Exploring gaps in surveillance of a small measles outbreak in Toronto, Canada.

In early 2015, an outbreak of 10 confirmed measles cases occurred in Toronto, Ontario. As part of the outbreak response, the Toronto Public Health staff conducted both traditional and supplementary case investigation activities. Despite this extensive effort, and unlike many previous measles outbreaks in Canada, neither the source case nor any confirmed epidemiologic links between cases were identified. The outbreak investigation brought to light potential gaps in the current measles surveillance and suggested approaches to future investigations: routine use of social media and other time-stamped resources to enhance case investigation; early and repeated targeted communication with primary care partners to improve case detection; and continued efforts to increase and maintain sufficient immunization coverage to interrupt transmission.