Longitudinal study of meningococcal carriage in adolescents and young adults in South Australia 2017-2020.

Background: This analysis investigated longitudinal changes in meningococcal carriage in adolescents in South Australia over 4 years.

Methods: Data from the "B Part of It" study, which included a state-wide cluster randomized controlled trial in secondary-school students (n = 34,489 in 2017 and 2018) and serial cross-sectional studies in school leavers aged 17-25 years (n = 4028 in 2019-2020). Individuals had oropharyngeal swabs collected annually. This study included two unique cohorts: (1) individuals enrolled in 2019, with three consecutive annual swabs taken in 2017, 2018 and 2019; and (2) individuals enrolled in 2020, with swabs taken in 2017, 2018, and 2020. Disease-associated N. meningitidis genogroups were identified using PCR and whole genome sequencing. Univariate analysis identified risk factors for recurrent carriage (≥2).

Results: Among school leavers, 50 (1.7%, total n = 2980) had carriage detected at successive visits. In participants with meningococcal carriage at successive visits, 38/50 (76.0%) had the same genogroup detected by porA PCR. Of those, 19 had the same MLST type and demonstrated minimal variation, indicating they most likely had sustained carriage of the same isolate (range 226 to 490 days, mean duration 352 [SD 51] days). In the 2019 school leaver cohort, 6.7% acquired carriage in their first year out of school compared to 3.3% in their final school year. Compared to single carriage detection, recurrent carriage was potentially more likely in older adolescents (16 compared to ≤15 years; OR = 1.97 (95%CI 1.0, 3.86); p = 0.048).

Conclusion: Whilst carriage is typically transient, some adolescents/young adults may have persistent carriage and are likely to be an important group in the transmission of meningococci.