Updating the meningitis belt: associations between environmental factors and epidemic meningitis risk across : Africa

TL;DR

This study updates the geographic risk of meningitis in Africa, finding that the meningitis belt remains in the Sahel, but potential expansion may reflect surveillance issues rather than real changes.

Contribution

The study provides an updated analysis of meningitis risk in Africa, incorporating recent data and environmental factors to assess changes over the past two decades.

Findings

The Sahelian region remains the highest risk area for meningitis outbreaks, with a probability >0.8.

Countries like the Republic of the Congo, Gabon, Liberia, and Angola showed moderate risk, suggesting a possible expansion of the meningitis belt.

Excluding the DRC due to poor case confirmation showed no surrounding countries at risk, highlighting the need for better laboratory testing.

Abstract

Previous analytical work, defining the distribution of meningitis epidemics in Africa is over 20 years old, with climate change representing an ongoing issue. We aim to update this analysis and determine if the meningitis belt geography and associated environmental risk factors have changed in the last two decades.

Epidemic bacterial meningitis data from 2003–2022 were provided by WHO-AFRO. Districts across Africa were coded 1 if they experienced a meningitis outbreak and 0 if not. Monthly means of windspeed, rainfall, dust, and humidity were processed into climatic profiles using k-means clustering. We undertook logistic regression with meningitis epidemic history as the dependent variable and k-means clusters of rainfall, dust, humidity, and windspeed, alongside land-cover type as independent variables. A sensitivity analysis was conducted, excluding the Democratic Republic of Congo (DRC), due to limited laboratory confirmation of cases.

Rainfall, dust, and humidity demonstrated the strongest statistical association with outbreaks and were included in our final model. With a probability cut-off >0.4, our model had specificity and sensitivity of 81.0% and 84.3%, respectively, in identifying districts having experienced a meningitis epidemic. The Sahelian region had the highest risk of meningitis outbreaks (probability >0.8), consistent with previous findings. The inclusion/exclusion of the DRC had a significant impact on our model. In the full model the Republic of the Congo, Gabon, Liberia, and Angola had a moderate risk of meningitis (probability >0.4), suggesting a possible south-westerly expansion of the belt. However, when the DRC was excluded, no countries surrounding the meningitis belt were at risk for outbreaks, highlight the importance of laboratory testing and case confirmation.

The apparent extension of risk beyond the belt possibly reflects surveillance limitations rather than alterations in disease ecology. Where possible, laboratory confirmation should be used to support surveillance of suspected meningitis outbreaks and cases.

Bacterial meningitis is a significant public health issue within sub-Saharan Africa, where outbreaks show a distinct seasonal pattern. Cases peak within the dry season, characterised by low humidity and high dust levels. Most cases occur within 26 countries spanning Senegal to Ethiopia, known as the meningitis belt. In this study, we evaluated the statistical association between history of meningitis outbreaks across Africa and climatic factors including rainfall, dust, humidity, wind speed and land cover type. We aimed to see if there had been any changes in at-risk regions of meningitis in line with climate change.

This study revealed that the central and western part of the Sahelian region of Africa, with lower rainfall and humidity, had the highest risk of meningitis outbreaks. This includes countries such as Burkina Faso, Chad, Gambia, Niger and Nigeria. Several countries bordering the meningitis belt had a moderate outbreak risk, suggesting a potential expansion. However, when we excluded outbreaks from the Democratic Republic of Congo due to poor case confirmation, no countries surrounding the meningitis belt were at risk for outbreaks. It is important to improve diagnostic capacity within meningitis outbreaks, to accurately assess disease risk across the continent.

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