Epidemiology of two decades of invasive meningococcal disease in the Republic of Ireland: an analysis of national surveillance data on laboratory-confirmed cases from 1996 to 2016.

D Bennett,S Morgan,R Cunney,S Cotter,P O'Lorcain,M Cafferkey

doi:10.1017/s0950268819000396

Abstract

We examined the epidemiology of invasive meningococcal disease (IMD) in the Republic of Ireland (ROI) between epidemiological year (EY) 1996/1997 and EY2015/2016. Over the 20 EYs, 3707 cases were reported with annual incidence rates per 100 000 peaking at 11.6 in EY1999/2000, decreasing significantly to 1.5 in EY2015/2016. The highest disease burden was in infants and children <5, whereas adults aged ⩾65 years experienced the highest case fatality ratio (CFR) of 15.7% but over the study period the median annual CFR remained low (4.4%). Meningococcal serogroup B (menB) dominated (78%), followed by menC (17%), menW (1%) and menY (1%). The incidence of menC IMD declined significantly in all age groups after menC vaccine introduction in 2000. MenB incidence also declined over the 20 EYs with decreasing trends in all age groups under 65, including an almost 50% decrease in infants over the final four EYs. IMD incidence in the ROI has declined, partly attributable to menC vaccination success, coupled with a spontaneous decline in menB. However, recent gradual increases in non-menB IMD and the introduction of vaccines targeting menB demand continued detailed surveillance to accurately monitor trends and to assess vaccine impact.

Highlights

Invasive meningococcal disease (IMD), defined as acute and severe infection by the bacterium Neisseria meningitidis, results in substantial neurological morbidity and mortality worldwide [1]
In the Republic of Ireland (ROI), national invasive meningococcal disease (IMD) surveillance is performed by the Health Protection Surveillance Centre (HPSC) and the Irish Meningitis and Sepsis Reference Laboratory (IMSRL)
In the ROI between EY1996/1997 and EY2015/2016, there were 3707 laboratory-confirmed cases of IMD recorded in the IMSRL

Summary

Introduction

Invasive meningococcal disease (IMD), defined as acute and severe infection by the bacterium Neisseria meningitidis, results in substantial neurological morbidity and mortality worldwide [1]. Six serogroups (A, B, C, W, Y and X) are responsible for the majority of IMD cases worldwide, distribution varies by geographical region and time, with most areas experiencing major cyclical fluctuations in the incidence of endemic disease and the occurrence of outbreaks and epidemics [1]. Laboratory-based epidemiological surveillance is important for monitoring changes in incidence and serogroup distribution over time. In the Republic of Ireland (ROI), national IMD surveillance is performed by the Health Protection Surveillance Centre (HPSC) and the Irish Meningitis and Sepsis Reference Laboratory (IMSRL). Prompted by an increase in the number of cases notified during the early 1990s, the IMSRL (originally named the Irish Meningococcal and Meningitis Reference Laboratory) was established in 1996 to provide a national service for the non-culture diagnosis of IMD using polymerase chain reaction (PCR) on specimens from normally sterile sites and species confirmation with serological and molecular epidemiological typing of N. meningitidis isolates.

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Conclusion