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      Exploring relationships between drought and epidemic cholera in Africa using generalised linear models


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          Temperature and precipitation are known to affect Vibrio cholerae outbreaks. Despite this, the impact of drought on outbreaks has been largely understudied. Africa is both drought and cholera prone and more research is needed in Africa to understand cholera dynamics in relation to drought.


          Here, we analyse a range of environmental and socioeconomic covariates and fit generalised linear models to publicly available national data, to test for associations with several indices of drought and make cholera outbreak projections to 2070 under three scenarios of global change, reflecting varying trajectories of CO 2 emissions, socio-economic development, and population growth.


          The best-fit model implies that drought is a significant risk factor for African cholera outbreaks, alongside positive effects of population, temperature and poverty and a negative effect of freshwater withdrawal. The projections show that following stringent emissions pathways and expanding sustainable development may reduce cholera outbreak occurrence in Africa, although these changes were spatially heterogeneous.


          Despite an effect of drought in explaining recent cholera outbreaks, future projections highlighted the potential for sustainable development gains to offset drought-related impacts on cholera risk. Future work should build on this research investigating the impacts of drought on cholera on a finer spatial scale and potential non-linear relationships, especially in high-burden countries which saw little cholera change in the scenario analysis.

          Supplementary Information

          The online version contains supplementary material available at 10.1186/s12879-021-06856-4.

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          Most cited references39

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          Little change in global drought over the past 60 years.

          Drought is expected to increase in frequency and severity in the future as a result of climate change, mainly as a consequence of decreases in regional precipitation but also because of increasing evaporation driven by global warming. Previous assessments of historic changes in drought over the late twentieth and early twenty-first centuries indicate that this may already be happening globally. In particular, calculations of the Palmer Drought Severity Index (PDSI) show a decrease in moisture globally since the 1970s with a commensurate increase in the area in drought that is attributed, in part, to global warming. The simplicity of the PDSI, which is calculated from a simple water-balance model forced by monthly precipitation and temperature data, makes it an attractive tool in large-scale drought assessments, but may give biased results in the context of climate change. Here we show that the previously reported increase in global drought is overestimated because the PDSI uses a simplified model of potential evaporation that responds only to changes in temperature and thus responds incorrectly to global warming in recent decades. More realistic calculations, based on the underlying physical principles that take into account changes in available energy, humidity and wind speed, suggest that there has been little change in drought over the past 60 years. The results have implications for how we interpret the impact of global warming on the hydrological cycle and its extremes, and may help to explain why palaeoclimate drought reconstructions based on tree-ring data diverge from the PDSI-based drought record in recent years.
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            The global burden of cholera.

            To estimate the global burden of cholera using population-based incidence data and reports. Countries with a recent history of cholera were classified as endemic or non-endemic, depending on whether they had reported cholera cases in at least three of the five most recent years. The percentages of the population in each country that lacked access to improved sanitation were used to compute the populations at risk for cholera, and incidence rates from published studies were applied to groups of countries to estimate the annual number of cholera cases in endemic countries. The estimates of cholera cases in non-endemic countries were based on the average numbers of cases reported from 2000 to 2008. Literature-based estimates of cholera case-fatality rates (CFRs) were used to compute the variance-weighted average cholera CFRs for estimating the number of cholera deaths. About 1.4 billion people are at risk for cholera in endemic countries. An estimated 2.8 million cholera cases occur annually in such countries (uncertainty range: 1.4-4.3) and an estimated 87,000 cholera cases occur in non-endemic countries. The incidence is estimated to be greatest in children less than 5 years of age. Every year about 91,000 people (uncertainty range: 28,000 to 142,000) die of cholera in endemic countries and 2500 people die of the disease in non-endemic countries. The global burden of cholera, as determined through a systematic review with clearly stated assumptions, is high. The findings of this study provide a contemporary basis for planning public health interventions to control cholera.
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              Rainfall and drought in equatorial east Africa during the past 1,100 years.

              Knowledge of natural long-term rainfall variability is essential for water-resource and land-use management in sub-humid regions of the world. In tropical Africa, data relevant to determining this variability are scarce because of the lack of long instrumental climate records and the limited potential of standard high-resolution proxy records such as tree rings and ice cores. Here we present a decade-scale reconstruction of rainfall and drought in equatorial east Africa over the past 1,100 years, based on lake-level and salinity fluctuations of Lake Naivasha (Kenya) inferred from three different palaeolimnological proxies: sediment stratigraphy and the species compositions of fossil diatom and midge assemblages. Our data indicate that, over the past millennium, equatorial east Africa has alternated between contrasting climate conditions, with significantly drier climate than today during the 'Medieval Warm Period' (approximately AD 1000-1270) and a relatively wet climate during the 'Little Ice Age' (approximately AD 1270-1850) which was interrupted by three prolonged dry episodes. We also find strong chronological links between the reconstructed history of natural long-term rainfall variation and the pre-colonial cultural history of east Africa, highlighting the importance of a detailed knowledge of natural long-term rainfall fluctuations for sustainable socio-economic development.

                Author and article information

                BMC Infect Dis
                BMC Infect Dis
                BMC Infectious Diseases
                BioMed Central (London )
                22 November 2021
                22 November 2021
                : 21
                : 1177
                [1 ]GRID grid.7445.2, ISNI 0000 0001 2113 8111, School of Public Health, , Imperial College London, ; Norfolk Place, London, W2 1PG UK
                [2 ]GRID grid.7445.2, ISNI 0000 0001 2113 8111, MRC Centre for Global Infectious Disease Analysis, School of Public Health, , Imperial College London, ; London, W2 1PG UK
                [3 ]GRID grid.83440.3b, ISNI 0000000121901201, Institute for Risk and Disaster Reduction, , University College London, ; London, WC1E 6BT UK
                [4 ]GRID grid.83440.3b, ISNI 0000000121901201, Institute for Globa Health, , University College London, ; London, UK
                [5 ]GRID grid.23048.3d, ISNI 0000 0004 0417 6230, University of Agder, ; Kristiansand, Norway
                [6 ]GRID grid.83440.3b, ISNI 0000000121901201, Department of Statistical Science, , University College London, ; London, WC1E 6BT UK
                [7 ]MRC Unit The Gambia at London School of Hygiene and Tropical Medicine, Atlantic Boulevard, Fajara, The Gambia
                © The Author(s) 2021

                Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

                : 8 July 2021
                : 8 November 2021
                Funded by: Natural Environmental Research Council
                Award ID: NE/S007415/1
                Award Recipient :
                Custom metadata
                © The Author(s) 2021

                Infectious disease & Microbiology
                public health,epidemiology,cholera,disease outbreaks,vibrio cholerae,droughts,climate change,africa


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