Definition and characterization of localised meningitis epidemics in Burkina Faso: a longitudinal retrospective study.

Haoua Tall,Judith E Mueller,Frank Drabo,Ludovic Kambou,Michèle Dramaix-Wilmet,Stéphane Hugonnet,Philippe Donnen

doi:10.1186/1471-2334-12-2

Abstract

BackgroundThe epidemiology of meningococcal meningitis in the African meningitis belt is characterised by seasonality, localised epidemics and epidemic waves. To facilitate research and surveillance, we aimed to develop a definition for localised epidemics to be used in real-time surveillance based on weekly case reports at the health centre level.MethodsWe used national routine surveillance data on suspected meningitis from January 2004 to December 2008 in six health districts in western and central Burkina Faso. We evaluated eight thresholds composed of weekly incidence rates at health centre level for their performance in predicting annual incidences of 0.4%and 0.8% in health centre areas. The eventually chosen definition was used to describe the spatiotemporal epidemiology and size of localised meningitis epidemics during the included district years.ResultsAmong eight weekly thresholds evaluated, a weekly incidence rate of 75 cases per 100,000 inhabitants during at least two consecutive weeks with at least 5 cases per week had 100% sensitivity and 98% specificity for predicting an annual incidence of at least 0.8% in health centres. Using this definition, localised epidemics were identified in all but one years during 2004-2008, concerned less than 10% of the districts' population and often were geographically dispersed. Where sufficient laboratory data were available, localised epidemics were exclusively due to meningococci.ConclusionsThis definition of localised epidemics a the health centre level will be useful for risk factor and modelling studies to understand the meningitis belt phenomenon and help documenting vaccine impact against epidemic meningitis where no widespread laboratory surveillance exists for quantifying disease reduction after vaccination.

Highlights

The epidemiology of meningococcal meningitis in the African meningitis belt is characterised by seasonality, localised epidemics and epidemic waves
We recently proposed a model [13] according to which localised epidemics are the basic unit of epidemic meningococcal disease and occasionally form epidemic waves that span larger regions if additional factors lead to a simultaneous widespread occurrence
We aimed to establish a definition of localised meningitis epidemics in the meningitis belt based on health centre data and to use this definition to describe the spatiotemporal epidemiology of localised epidemics in Burkina Faso over half a decade

Summary

Introduction

The epidemiology of meningococcal meningitis in the African meningitis belt is characterised by seasonality, localised epidemics and epidemic waves. Apart from the current introduction of serogroup A meningococcal conjugate vaccine in Mali, Burkina Faso and Niger, three core countries of the meningitis belt, emergency mass vaccination campaigns with polysaccharide. To this purpose, all health centres in the countries above report on a weekly basis suspected cases of bacterial meningitis to the sanitary districts, where data are aggregated, analysed and sent to the national level [8]. We aimed to establish a definition of localised meningitis epidemics in the meningitis belt based on health centre data and to use this definition to describe the spatiotemporal epidemiology of localised epidemics in Burkina Faso over half a decade

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