The environmental drivers of bacterial meningitis epidemics in the Democratic Republic of Congo, central Africa

Abstract

Introduction

Bacterial meningitis still constitutes an important threat in Africa. In the meningitis belt, a clear seasonal pattern in the incidence of meningococcal disease during the dry season has been previously correlated with several environmental parameters like dust and sand particles as well as the Harmattan winds. In parallel, the evidence of seasonality in meningitis dynamics and its environmental variables remain poorly studied outside the meningitis belt. This study explores several environmental factors associated with meningitis cases in the Democratic Republic of Congo (DRC), central Africa, outside the meningitis belt area.

Methods

Non-parametric Kruskal-Wallis’ tests were used to establish the difference between the different health zones, climate and vegetation types in relation to both the number of cases and attack rates for the period 2000–2018. The relationships between the number of meningitis cases for the different health zones and environmental and socio-economical parameters collected were modeled using different generalized linear (GLMs) and generalized linear mixed models (GLMMs), and different error structure in the different models, i.e., Poisson, binomial negative, zero-inflated binomial negative and more elaborated multi-hierarchical zero-inflated binomial negative models, with randomization of certain parameters or factors (health zones, vegetation and climate types). Comparing the different statistical models, the model with the smallest Akaike’s information criterion (AIC) were selected as the best ones. 515 different health zones from 26 distinct provinces were considered for the construction of the different GLM and GLMM models.

Results

Non-parametric bivariate statistics showed that there were more meningitis cases in urban health zones than in rural conditions ( χ ² = 6.910, p-value = 0.009), in areas dominated by savannah landscape than in areas with dense forest or forest in mountainous areas ( χ ² = 15.185, p-value = 0.001), and with no significant difference between climate types ( χ ² = 1.211, p-value = 0,449). Additionally, no significant difference was observed for attack rate between the two types of heath zones ( χ ² = 0.982, p-value = 0.322). Conversely, strong differences in attack rate values were obtained for vegetation types ( χ ² = 13.627, p-value = 0,001) and climate types ( χ ² = 13.627, p-value = 0,001). This work demonstrates that, all other parameters kept constant, an urban health zone located at high latitude and longitude eastwards, located at low-altitude like in valley ecosystems predominantly covered by savannah biome, with a humid tropical climate are at higher risk for the development of meningitis. In addition, the regions with mean range temperature and a population with a low index of economic well-being (IEW) constitute the perfect conditions for the development of meningitis in DRC.

Conclusion

In a context of global environmental change, particularly climate change, our findings tend to show that an interplay of different environmental and socio-economic drivers are important to consider in the epidemiology of bacterial meningitis epidemics in DRC. This information is important to help improving meningitis control strategies in a large country located outside of the so-called meningitis belt.

Author summary

Bacterial meningitis remains an international public health threat. The most affected area worldwide is the Sahelian region between Senegal and Ethiopia called the meningitis belt. In parallel recurrent epidemics have also occurred out of the belt in Africa for the last twenty years. While environmental, socioeconomic and demographic factors are well described to explain the epidemiology of meningitis in the belt, very few studies have focused on the role of these factors to understand meningitis epidemics outside of the belt. Based on epidemiological, socio-economic, demographic and environmental data collected for the period 2000–2018 in the Democratic Republic of Congo (DRC), we used different statistical methods to explore the links between meningitis cases and the different explored factors. Our results showed that urbanized areas where populations have a low economic index of well-being, high latitude and longitude eastwards, medium to low altitude level, savannah-type vegetation, medium temperature value, are risk factors of meningitis outbreaks from North to South in the DRC. This information is important to help improving meningitis control strategies in a large country located outside the so-called meningitis belt.