Environmental Covariates Associated with Meningococcal Meningitis

Abstract

The “Meningitis Belt” is a region of sub-Saharan Africa that suffers the greatest mortality and morbidity due to meningococcal meningitis (MCM). MCM is strongly characterized by seasonality, in which outbreaks and epidemics of the disease typically occur in the dry season, from January until April. While there have been numerous studies investigating the impact of environmental covariates on the MCM incidence rates in Africa, it is still relatively unclear which seasonal factors are the most important to consider in understanding the severity of meningitis outbreaks. Thus, this paper focuses on determining on the environmental covariates that are the most strongly associated with the meningitis incidence rate in areas throughout Burkina Faso, during 2003-2007. Nested models with these seasonal variables were constructed using RStudio. In addition, due to the hypothesized role they play in affecting a population’s susceptibility to MCM, two environmental covariates - the dust concentration and the relative humidity - were also investigated further by creating graphs that plot the trends in dust concentration, relative humidity, and incidence rate. Results from the model analyses showed that the disease incidence rate, dust concentration, relative humidity, the type of season, and the interaction between the relative humidity and season two weeks prior to a given week were strongly associated with the meningitis incidence rate. On the other hand, model analyses of these variables two months prior to a given week showed that only MCM incidence rate, the type of season, and the interaction between relative humidity and season two months prior were significantly associated with the disease incidence rate. Graphs plotting the disease incidence rate, relative humidity, and dust concentrations showed that the dusty season (the period of time in which dust concentration rises and falls rapidly) is generally longer than the meningitis season, and that the yearly minimums of relative humidity during the dry season precede the peaks of MCM incidence rates by 2-4 weeks. Lastly, the results showed that neither increases in dust concentration and decreases in relative humidity are proportional to increases in disease incidence rates. This study provides an important means of disease monitoring in Africa: since the severity of the outbreaks vary from year to year, gaining a better understanding of the environmental covariates strongly associated with the disease incidence rate can provide crucial information for constructing health policies to protect an estimated 300 million at risk for this disease in the Meningitis Belt.