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L'article du mois (septembre 2018)

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

Maxime Woringer, Nadège Martiny, Souleymane Porgho, Brice W.Bicaba, Avner Bar-Hen, and Judith E.Mueller

BACKGROUND: Bacterial meningitis causes a high burden of disease in the African meningitis belt, with regular seasonal hyperendemicity and spo-radic short, but intense, localized epidemics during the late dry season occurring at a small spatial scale [i.e., below the district level, in individual health centers (HCs)]. In addition, epidemic waves with larger geographic extent occur every 7–10 y. Although atmospheric dust load is thought to be an essential factor for hyperendemicity, its role for localized epidemics remains hypothetic.

 

OBJECTIVES: Our goal was to evaluate the association of localized meningitis epidemics in HC catchment areas with the dust load and the occurrence of cases in the same population early in the dry season.

METHODS: We compiled weekly reported cases of suspected bacterial meningitis at the HC resolution for 14 districts of Burkina Faso for the period 2004–2014. Using logistic regression, we evaluated the association of epidemic HC-weeks with atmospheric dust [approximated by the aerosol optical thickness (AOT) satellite product] and with the observation of early meningitis cases during October–December.

RESULTS: Although AOT was strongly associated with epidemic HC-weeks in crude analyses across all HC-weeks during the meningitis season [odds ratio (OR) = 6:82; 95% CI: 4.90, 9.50], the association was no longer apparent when controlling for calendar week (OR = 0:92; 95% CI: 0.60, 1.50). The number of early meningitis cases reported during October–December was associated with epidemic HC-weeks in the same HC catchment area during January–May of the following year (OR for each additional early case = 1:14; 95% CI: 1.06, 1.21).

CONCLUSIONS: Spatial variations of atmospheric dust load do not seem to be a factor in the occurrence of localized meningitis epidemics, and the fac-tor triggering them remains to be identified. The pathophysiological mechanism linking early cases to localized epidemics is not understood, but their occurrence and number of early cases could be an indicator for epidemic risk.

 

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Le Centre de Recherches de Climatologie (CRC) est une équipe de recherche de l'UMR6282 Biogéosciences (CNRS / Université de Bourgogne). Le CRC travaille sur la détection, l'attribution et la prévision du signal climatique et de ses impacts dans l'actuel et le futur. Ses activités sont centrées autour de la régionalisation du climat observé et simulé.

Le CRC est structuré en deux axes thématiques qui mettent en œuvre des méthodes permettant de passer de l'information large échelle (objet des travaux de l'équipe « Dynamique du Climat ») à une information d'échelle plus fine permettant d'évaluer les impacts (équipe « Impacts Climatiques »). Cette méthodologie relève de la statistique (méthodes statistico-dynamiques sur les sorties de modèles; statistiques spatiales;  désagrégation), de l'analyse spatiale (SIG opérateurs d'analyse spatiale vecteur et raster; interpolation spatiale mécaniste ou statistique), ou de la modélisation numérique du climat (modèles régionaux MM5 et WRF, modèle global Arpege-Climat).

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