De Wals, P., Gilquin, C., Demaeyer, S., Bouckaert, A., Noël, A., Lechat, MF., & Lafontaine, A. (1983). Longitudinal-study of Asymptomatic Meningococcal Carriage in 2 Belgian Populations of Schoolchildren. Journal of Infection, 6(2), 147-156. https://doi.org/10.1016/S0163-4453(83)92756-1 (Original work published 1983)