Association between population prevalence of smoking and incidence of meningococcal disease in Norway, Sweden, Denmark and the Netherlands between 1975 and 2009: a population-based time series analysis. - Norheim G; Sadarangani M; Omar O; Yu LM; Mølbak K; Howitz M; Olcén P; Haglund M; van der Ende A; Pollard AJ (BMJ open, 2014)