Climatic Factors in Relation to Diarrhea for Informed Public Health Decision-Making: A Novel Methodological Approach

Background Diarrheal disease is one of the leading causes of morbidity and mortality globally, particularly in children under 5 years of age. Factors related to diarrheal disease incidence include infection, malnutrition, and exposure to contaminated water and food. Climate factors also contribute to diarrheal disease. Objectives We aimed to explore the relationship between temperature, precipitation and diarrhea case counts of hospital admissions among vulnerable communities living in a rural setting in South Africa. Methods We applied a novel approach of ‘contour analysis’ to visually examine simultaneous observations in frequencies of anomalously high and low diarrhea case counts occurring in a season and assigning colors to differences that were statistically significant based on chi-squared test results. Results There was a significantly positive difference between high and low ‘groups’ when there was a lack of rain (0 mm of cumulative rain) for 1 to 2 weeks in winter for children under 5. Diarrhea prevalence was greater among children under 5 years when conditions were hotter than usual during winter and spring. Discussion Dry conditions may lead to increased water storage raising the risks of water contamination. Reduced use of water for personal hygiene and cleaning of outdoor pit latrines affect sanitation quality. Rural communities require adequate and uninterrupted water provision and healthcare providers should raise awareness about potential diarrheal risks especially during the dry season.


Introduction
An estimated 3.4 million people die from diarrheal and other water-related diseases each year 60 [1]. Diarrheal disease is responsible globally for 21% of deaths per year in children younger 61 than 5 years of age [2] and is ranked as the third leading cause of death in this age group in South 62 Africa [3]. The transmission of diarrheal disease is determined by factors related to, among 63 others, weather variables, the vector and agent, socio-economic and ecological conditions, and 64 intrinsic human immunity [4]. association of diarrheal incidence with high average temperature of 36 °C and above, and high 77 cumulative monthly rainfall at 57 mm and above. In Vietnam, considerable spatial heterogeneity 78 existed in the risk of all-cause for diarrhoea across districts investigated with low elevation and 79 differential responses to flooding and air temperature, and humidity drove further spatial 80 heterogeneity in diarrheal disease risk [11]. In Ecuador, heavy rainfall events were associated 81 with increased diarrhoea incidence following dry periods and decreased diarrhoea incidence 82 following wet periods [12].

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Children and especially children under 5 years of age, are particularly susceptible to 84 diarrheal disease. In a study using Demographic and Health Survey data from 14 Sub-Saharan 85 countries, regional prevalence of diarrhoea in children under three years of age was considered in 86 relation to variations in precipitation and temperature [13]. Results showed that shortage of 87 rainfall in the dry season increased the prevalence of diarrhoea across Sub-Saharan Africa. Such 88 shortages occur in many regions when rainfall is average to below-average relative to the long-4 89 term monthly-mean. The results also showed that an increase in monthly-average maximum 90 temperature raises the prevalence of diarrhoea while an increase in monthly minimum 91 temperature reduces the number of diarrheal cases [13]. Maximum temperature and extreme 92 rainfall days were also reported as strongly related to diarrhoea-associated morbidity with the 93 impact of maximum temperature on diarrhoea-associated morbidity appearing primarily among 94 children (0-14 years) and older adults (40-64 years), but with relatively less effects on adults 95 (15-39 years) [14].

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Since diarrheal disease is a major cause of morbidity and mortality, particularly among 97 children under 5 years of age in developing countries and given that climate change-related 98 health consequences of diarrheal diseases are projected to pose significant risks to future 99 populations [15] we set out to explore the relationship between climate factors (temperature and 100 precipitation) and diarrhoea prevalence among vulnerable rural communities in South Africa 101 located in a subtropical setting, using a novel approach. In this study, we used "contours" to 102 visualize frequencies of diarrhoea anomalies occurring in a season and assigned colors to 103 differences that were statistically significant based on chi-squared test results. Meteorologists

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All diarrhea cases were extracted from the hospital admission records database for cases 123 defined as diarrhoea using the criteria and terms provided by a South African medical doctor.  were removed referring to the "noise", "irregular" or "remainder", which is thus termed as the 158 random component, i.e. the anomalies. Anomalies were therefore calculated according to 159 Equation 1: Where: A is the Anomaly, S is the seasonal component, T is the trend component, and t is time 162 (or week). High weekly anomalies were inferred as 'higher than normal' diarrhea case counts 163 and low anomalies were inferred as 'lower than normal', where 'normal" refers to the long-term 164 average for the corresponding period/week i.e. the first component discussed above. In addition, 165 we discarded anomalies that were less than one standard deviation from the mean to retain 166 anomalously extreme high or low incidence. Then we segregated the high and low incidence  For all weeks within each season, across the data set, we counted for precipitation how 171 many times it rained on average 'y' mm over 'x' consecutive weeks (with x going from 1 to 10 172 weeks, and y for decile increments of the range of precipitation values) and tested these findings 173 for statistically significant differences between the two groups of incidence category (i.e. high or 174 low  noticeably at a lag of 5 weeks with 4 to 9 weeks of consecutively no rain ( Figure 6). Significant 219 differences were not seen in DJF ( Figure S3) and MAM showed differences only at 4 and 8 for 8 220 to 10 weeks of consecutive cumulative rain of 14 -26 mm ( Figure S4). We set out to explore the relationship between precipitation / temperature and case counts of  In addition, the wetter conditions may lead to increased risks of water contamination. Under-269 developed infrastructure and illegal connections to water supply pipes may also lead to 270 contaminated water [26]. It is possible that children under the age of 5 are more vulnerable to 271 such conditions. However, these assumptions remained to be verified among the communities 272 served by the two hospitals from which data were drawn for use in the analyses presented here.  In summary, using a novel approach of analysis we detected trends in patterns of 301 precipitation and temperature in relation to diarrhea prevalence for two separate age groups.

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Children under 5 years of age were especially vulnerable to diarrhea during very dry, hot 303 conditions as well as when conditions were wetter than usual. We noted that local living, The authors declare they have no actual or potential conflicting interests.