Invasive pneumococcal disease surveillance in Canada, 2023

Invasive pneumococcal disease (IPD), which is caused by Streptococcus pneumoniae, has been a nationally notifiable disease in Canada since 2000. This report summarizes the demographics, serotypes and antimicrobial resistance of IPD isolates collected in Canada in 2023.

The Public Health Agency of Canada's National Microbiology Laboratory (Winnipeg, Manitoba) collaborates with provincial and territorial public health laboratories to conduct national surveillance of IPD. Serotypes and minimum inhibitory concentrations were obtained from whole genome sequencing data.

The incidence of IPD in Canada was 10.2 cases per 100,000 population in 2022, increasing from the low rate of 5.6 cases per 100,000 population in 2021. A total of 4,760 IPD isolates were collected during 2023. The most common serotypes overall were 3 (12.3%, n=587), 4 (12.2%, n=580), 22F (8.2%, n=391) and 9V (7.1%, n=340). Serotypes 4 (7.1%-12.2%, p<0.0001) and 9V (1.3%-7.1%, p<0.0001) also increased significantly in prevalence since 2019, resulting in an overall increase in the proportion of PCV15 and PCV20/non-V116 serotypes causing disease. The highest rates of antimicrobial resistance in 2023 were seen with clarithromycin (25.8%), doxycycline (17.5%) and trimethoprim/sulfamethoxazole (15.9%). Multidrug-resistance continued to increase from 2019 to 2023 (8.4%-13.2%, p<0.0001) and rates were highest in serotypes 9V, 15A, 19A, 23A and 35B.

The high number of IPD cases collected in 2023 represents a return to pre-SARS-CoV-2 pandemic disease activity. Several serotypes included in previous conjugate vaccine formulations are highly common or are increased in prevalence, including 3, 4 and 9V. Continued surveillance of pneumococcal serotypes is imperative to evaluate vaccine effectiveness, particularly as new vaccine formulations are approved and integrated into immunization schedules in Canada.