Climate Change and Cholera in Tanzania

Increased rainfall and temperatures are widely recognized to increase the risk of diarrheal diseases.  Trærup et al. (2011) used historical climatic and cholera data along with socioeconomic data in order to predict the future risk of Cholera in Tanzania under a moderate climate change scenario. The results revealed a significant relationship between temperature and the incidence of cholera. It was found that a 1ºC increase would cause a 15–20% risk increase. In addition, Trærup et al. predicted the costs associated with the disease, which were estimated to account for 0.32–1.4 % of GDP in Tanzania in 2030.—Simone Berkovitz
Trærup S., Ortiz R., Markandya A., 2011.The Costs of Climate Change: A Study of Cholera in Tanzania. Int. J. Environ. Res. Public Health 8, 4386–4405.

Recent studies have associated temperature and rainfall variability with the prevalence of diarrhea and cholera transmission. Therefore, climate change is of particular concern when studying the impacts of cholera and other waterborne diseases.  Higher air temperatures lead to higher water temperatures in shallow bodies of water, which become bacterial breeding grounds. In addition, increased flooding due to climate change can contaminate drinking water, which increases the disease prevalence. Trærup et al. utilize Tanzanian local national data in order to assess the impacts of climate change on cholera prevalence, and the economic costs of the disease. The authors used primary data sources in order to estimate the relationship between climate change and cholera, and then made future predictions for 2030.
The study utilized historical data on deaths and cases of cholera, rainfall and temperature recordings, and socioeconomic data. The data for cases were converted into a graph that showed seasonal distribution over the past 6 years. The second graph showed the average monthly rainfall over the same 6-year span. These figures indicated that from June to October, lower total rainfall coincided with fewer cases of cholera.
In order to analyze and predict the impact of climate change on the burden of cholera, two separate economic and climate scenarios were used. Scenario C2030, was a baseline scenario that did not include the effects of climate change. This scenario incorporated WHO estimates, which included predictions for socio-economic growth that would lower the burden of the disease. Using these data, the authors were able to calculate the average case fatality rate (CFR) for cholera in Tanzania. In addition, population health was estimated by combining data on mortality and non-fatal health outcomes in a single figure, which was measured as Disability-Adjusted Life-Years (DALY). DALY measures the disease burden and combines years of life lost (YLL) from premature deaths with years of life lived with disabilities (YLD). Scenario C1, accounts for climate change when estimating the number of cholera cases, deaths, and DALYs. This scenario assumes a 1ºC and 2ºCtemperature increase based on the IPCC, A1B middle scenario temperature predictions for Tanzania on 2030. The burden of the disease attributable to climate change was found by calculating the Impact Fraction, which is the proportion of the population exposed, combined with the burden of climate change.. A negative binomial regression model was used in order to estimate the incidences of cholera cases or deaths in a time period, based upon the rainfall, temperature, and a vector of socioeconomic factors.
In order to assess the total costs of the health impacts attributable to climate change, Trærup et al. looked at reactive adaptation measures in addition to the costs of residual damages. The authors discussed the costs of preventive measures, however these measures were not taken into account because it was assumed that they were included in economic development. Reactive measures included the cost of treatment per case. The loss of short-term productivity was accounted for by looking at lost working hours. In addition, the cost of lives lost was calculated by using a GDP-adjusted Value of Statistical Life (VOSL) method, which broadly measures the individual’s willingness to pay to reduce the risk of death in order to place a value on the impacts of mortality.
According to the statistical tests, Trærup et al. found that cholera cases were positively correlated with temperature, however the correlation between cases and rainfall was found to be not significant. This suggests that cholera cases in Tanzania are better explained by temperature rather than amount of rainfall. In the first model, it was found that an increase equal to 1ºC would increase the relative risk for cholera cases in Tanzania by 29%, while the second model predicted that a 1ºC increase would increase the relative risk by 15%. A table was created, which displayed the estimated number of diseases in the year 2030, in each of the different scenarios. The second table displayed the estimated costs in 2030 for the different scenarios. It is revealed that a 1ºC temperature increase costs 44–47 % less than a 2ºC increase. The authors note that preventative measures are not included and most likely there are other health variables that are going to be affected by climate change which were not accounted for. This study confirms the correlation between environmental risk factors and cholera in Africa and reveals how climate change will exacerbate the situation. Climate change will negatively influence overall human health and cause large additional economic burdens. 

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