Post-pandemic increase in invasive group A strep infections in New Zealand.

Background: Since October 2022, multiple high-income countries have reported an increase in invasive group A streptococcal (iGAS) infections. This study describes trends in iGAS infections in Aotearoa New Zealand (NZ) between 2017 and 2023, and examines associations of iGAS incidence, COVID-19 eras, and acute respiratory infections (ARI).

Methods: Analyses include national-level surveillance data on iGAS and ARI. Multivariable Poisson regression was used to examine relationships between COVID-19 era and iGAS incidence, and Pearson pairwise correlations were calculated to examine trends between ARI and iGAS.

Findings: A sharp increase in iGAS was observed in 2023, with notable increases among children aged under ten years. Indigenous Māori and Pacific peoples were disproportionately affected. emm1 and emm12 were commonly reported in 2022-2023. Compared to pre-pandemic, iGAS decreased significantly during the COVID-19 restrictions era and increased once COVID-19 restrictions were relaxed, after adjusting for ethnicity, sex, and age. ARI was moderately correlated with iGAS (r = 0∙55) in 2022-2023.

Interpretation: Though delayed, NZ's recent iGAS trends mirror those seen in the 2022/2023 multi-country iGAS surge. These findings expand existing research, suggesting a link between the easing of COVID-19 measures, increased ARI circulation, and the rise in iGAS. Continued and improved iGAS surveillance, is needed to better understand iGAS epidemiology and support public health response. iGAS in NZ will become notifiable in late 2024, which should help improve iGAS monitoring and support public health response.

Funding: This research received no specific funding, though iGAS surveillance and typing in NZ is funded by the Ministry of Health, which was not involved in the analysis, interpretation, design, or any aspect of this study. No authors were paid to write this manuscript.