Outbreak of invasive Streptococcus pneumoniae among an inner-city population in Victoria, British Columbia, 2016-2017.

Background Invasive pneumococcal disease (IPD) is a significant cause of morbidity and mortality; however, outbreaks of IPD are relatively rare. Homelessness and substance use are known risk factors for IPD and have been associated with several outbreaks in Canada, despite national recommendations for routine childhood and targeted adult pneumococcal vaccination. Objectives To describe the epidemiology and public health challenges related to an outbreak of novel serotype 4 IPD in a homeless and unstably housed population in Victoria, British Columbia during the autumn and winter of 2016-2017. Results Prospective, enhanced surveillance was initiated for laboratory confirmed cases reported to public health, including variables recording housing status and substance use. Thirty-three cases of serotype 4 IPD within the Victoria area were reported to public health between August 1, 2016 and September 1, 2017. Compared with other serotypes, these cases were more likely to be middle-aged, homeless or unstably housed, and to have a recent history of substance use. A targeted pneumococcal vaccination campaign was initiated in collaboration with external community organizations; however, these initiatives were challenged by incomplete data and staffing constraints. Conclusion This report illustrates an outbreak of serotype 4 IPD among an inner-city population with multiple risk factors, including homelessness, unstable housing and substance use. Given the challenges controlling the outbreak, outreach capacity and pneumococcal vaccination coverage is needed among this marginalized population.