Global epidemiology of capsular group W meningococcal disease, 1970-2014: emergence and persistence of hypervirulent ST-11 lineage

Following an outbreak in Mecca Saudi Arabia in 2000, meningococcal strains expressing capsular group W (W) emerged as a major cause of invasive meningococcal disease (IMD) worldwide. This essay presents a critical review of studies reporting IMD surveillance data spanning four decades and places in context the recent findings of WGS studies to the epidemiology of group W IMD. This report will be of use to Public Health experts in several countries currently facing a rise in number of W cc11 cases and persistence of sporadic group W cases. \ud The Saudi Arabian outbreak strain (Hajj clone) belonging to the ST-11 clonal complex (cc11) is similar to W cc11 causing occasional sporadic disease before 2000. Since 2000, W cc11 has caused large meningococcal disease epidemics in the African meningitis belt and endemic disease in South America, Europe and China. Traditional molecular epidemiologic typing suggested that a majority of current W cc11 burden represented global spread of the Hajj clone. However, recent whole genome sequencing (WGS) analyses revealed significant genetic heterogeneity among global W cc11 strains. While continued spread of Hajj-related strains occurs in the Middle East, the meningitis belt and South Africa have co-circulation of the Hajj clone and other unrelated W cc11 strains and South America, the UK and France share a genetically distinct W c11 strain. Other W lineages persist in low numbers in Europe, North America and the meningitis belt. In summary, WGS is helping to unravel the complex genomic epidemiology of group W meningococcal strains. Wider application of WGS and strengthening of global IMD surveillance is necessary to monitor the continued evolution of group W lineages. There is need for a vaccine that is protective against group W in the meningitis belt.\ud Public Health relevance: This essay presents a critical review of studies reporting IMD surveillance data spanning four decades and places in context the recent findings of WGS studies to the epidemiology of group W IMD. This report will be of use to Public Health surveillance and policy professionals in several countries currently facing a rise in number of W cc11 cases and persistence of sporadic group W cases. Data presented in this review also provides evidence in support of introduction of group W in the African meningitis belt