Atmospheric Dust, Early Cases, and Localized Meningitis Epidemics in the African Meningitis Belt: An Analysis Using High Spatial Resolution Data

By Woringer, Maxime; Martiny, Nadege et al. | Environmental Health Perspectives, September 2018 | Go to article overview

Atmospheric Dust, Early Cases, and Localized Meningitis Epidemics in the African Meningitis Belt: An Analysis Using High Spatial Resolution Data


Woringer, Maxime, Martiny, Nadege, Porgho, Souleymane, Bicaba, Brice W., Bar-Hen, Avner, Mueller, Judith E., Environmental Health Perspectives


Introduction

Bacterial meningitis affects tens of thousands of people every year, with a case fatality rate of >10% (WHO 2014). The majority of these cases occur in the African meningitis belt, an area characterized by a single long dry season with intense dust events (Lapeyssonnie 1963; Molesworth et al. 2002) that spans sub-Saharan Africa from Senegal to Ethiopia. In this region, bacterial meningitis exhibits a complex epidemiological pattern. During the rainy season (June-September), endemic meningitis cases occur at a rate that is similar to those of other areas of the world. However, during the late dry season (January-May) the incidence of meningitis due to Neisseria meningitidis (meningococcal meningitis) and Streptococcus pneumoniae increases 10- to 100-fold throughout the meningitis belt. In addition, localized epidemics of meningococcal meningitis with incidence rates that imply an additional 10- to 100-fold increase may occur within smaller areas (Tall et al. 2012). Finally, epidemic waves that cover larger geographic areas occur every 7-10 y, with some variation in the specific regions affected by each periodic wave (Lapeyssonnie 1963).

Although the introduction of a meningococcal serogoup A conjugate vaccine in 2010 appears to have eliminated serogroup A meningitis epidemics in the meningitis belt countries (Diomande et al. 2015), epidemics due to other serogroups (W, X, and C) continue to occur (Xie et al. 2013; Kretz et al. 2016). A better understanding of the factors that contribute to ongoing meningitis outbreaks is needed to more effectively control them and to optimize future vaccination strategies.

No widely accepted explanation for the meningococcal epidemiology exists today (Agier et al. 2017). A hypothetical explanatory model that combines factors at different time scales and spatial scales has been proposed (Mueller and Gessner 2010). These factors are low relative humidity (typically below 20% during the late dry season) and exposure to atmospheric dust through the Harmattan winds for hyperendemic seasonality of meningitis incidences (Savory et al. 2006; Yaka et al. 2008; Martiny and Chiapello 2013; Agier et al. 2012; Garcia-Pando et al. 2014; Deroubaix et al. 2013), coinfections for localized outbreaks and genetic variations of meningococcal strains for epidemic waves. Furthermore, exposure to domestic smoke (Hodgson et al. 2001; Mueller et al. 2011) has been found to increase individual risk of bacterial meningitis. Several of these factors can be seen in analogy to indoor smoke and environmental dust as risk factors of pneumonia and other respiratory morbidity (Gordon et al. 2014; Trianti et al. 2017). In addition, ecological studies suggest that the occurrence of cases during the early dry season (before January) is associated with the risk of subsequent epidemics during January-May (Yaka et al. 2008; Paireau et al. 2014; Garcia-Pando et al. 2014).

A considerable body of evidence based on weekly or monthly meningitis surveillance data at the national or district level thus supports the essential role of environmental factors in the seasonality of epidemic meningitis. However, it is unclear so far whether the environment accounts only for seasonal hyperendemicity or also for the occurrence of localized epidemics and of epidemic waves. Such questions require a distinction between seasonality and epidemic events (and their respective onset) that needs to be based on high-resolution data that allow identification of individual localized epidemics. Findings from two recent studies suggested that the use of case counts at the health center (HC) level facilitates research on the spatial and temporal dynamics of localized meningococcal meningitis epidemics (Tall et al. 2012; Paireau et al. 2014). An individual HC is the smallest administrative health division in most countries of the meningitis belt and comprises primary health posts, hospitals, and clinics. For the present analysis, we used high-resolution case-count data to estimate associations of localized meningitis epidemics with dust load and the occurrence of early cases (reported during October-December). …

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