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Rising incidence of invasive meningococcal disease caused by Neisseria meningitidis serogroup W in Victoria

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Invasive meningococcal disease (IMD) caused by Neisseria meningitidis is one of the most rapidly progressive sepsis syndromes, often resulting in significant morbidity and mortality. Since the introduction of meningococcal C conjugate vaccine in 2003, IMD in Victoria has decreased from 2.5/100 000 to 0.6/100 000 population.1 Epidemiological typing of N. meningitidis isolates is by serogroup, multilocus sequence typing and finetyping.

In Victoria, from January 2014 to September 2015, the number of cases of IMD caused by N. meningitidis serogroup W (MenW) increased. Previously uncommon (< 5% of IMD overall in the period from 2008 to 2013 [n = 260]), MenW as a proportion of IMD has increased: four of 33 cases in 2014 and 12 of 41 cases in 2015 (Microbiological Diagnostic Unit, University of Melbourne, unpublished data). Over this period, the median age of cases was 55 years, compared with 19 years for serogroup B, with many non-classical presentations including pneumonia, epiglottitis, septic arthritis and pericarditis. There has been one death in a healthy young adult. No epidemiological links between cases have been observed (Victorian Government Department of Health and Human Services [DHHS], unpublished data).

Globally, MenW has been responsible for an increasing proportion of IMD since outbreaks associated with the Hajj pilgrimage in 2000.