565448 research-article2015
APHXXX10.1177/1010539514565448Asia-Pacific Journal of Public HealthPhung et al
Review Article
Climate Change, Water Quality, and Water-Related Diseases in the Mekong Delta Basin: A Systematic Review
Asia-Pacific Journal of Public Health 2015, Vol. 27(3) 265–276 © 2015 APJPH Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/1010539514565448 aph.sagepub.com
Dung Phung, PhD1, Cunrui Huang, PhD1, Shannon Rutherford, PhD1, Cordia Chu, PhD1, Xiaoming Wang, PhD2, and Minh Nguyen, DrEng2
Abstract Mekong Delta Basin (MDB) is vulnerable to extreme climate and hydrological events. The objectives of this review are to understand of water related health effects exacerbated by climate change and the gaps of knowledge on the relationships between climate conditions, water quality, and water-related diseases in the MDB. The findings indicate that a few studies with qualitative emphases on the relationships between climate and water quality have been conducted in MDB, and they are insufficient to describe the pattern of climate-disease relationship. The diseases caused by chemical contaminants in relation to changes of climate conditions are neglected in MDB. We suggest further studies to examine the influence of short-term variation of climate conditions on water quality and water-related diseases for the purpose of public health and medical prevention, and due to the trans-boundary nature of MDB, developing partnership in data sharing and research collaboration among MDBs countries should be prioritized. Keywords climate change, water quality, water-related diseases, Mekong Delta Basin, Mekong Delta River
Introduction The Mekong Delta Basin (MDB; Figure 1) is vulnerable to extreme climate and hydrological events.1 The air temperature in the MDB is predicted to increase a few degrees Celsius in the period from 2030 to 2100.2 The sea level in the MDB could rise up to 1 m by the 2100s.3 A wide variation in rainfall is projected across the MDB.2-5 Flood duration has been suggested to increase
1Griffith
University, Nathan Campus, Brisbane, Queensland, Australia Scientific and Industrial Research Organization (CSIRO), Canberra, Australia
2Commonwealth
Corresponding Authors: Dung Phung, Centre for Environment and Population Health, Griffith School of Environment, Griffith University, Nathan campus, 179 Kessels Road, Nathan, Brisbane, Queensland 4111, Australia. Email: [email protected] Cunrui Huang, School of Public Health, Sun Yat-sen University, 74 Zhongshan Road #2, Guangzhou, Guangdong Province 510080, China. Email: [email protected]
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Figure 1. Mekong Delta Basin (Source: Eastham et al, 2008).4
in all the simulated scenarios.3 Besides the annual flood pulse, increasing likelihood of extreme floods was predicted.4,6 Droughts were also predicted to be more intensified in MDB.4 Changes of climate can negatively affect water quality in river basin7 because they cause alteration in the pattern and distribution of rainfall over the entire basin, leading to changes in river flow volume, leading to changes in the transport of biological pathogens.8,9 The long drought periods have also negative effects on water quality such as temperature, dissolved oxygen, biochemical oxygen demand, and concentration of pathogens and certain chemical compounds.10,11 As a consequence, these climate changes are considered to contribute to elevating the risk of waterborne diseases due to the variation of pathogen concentration and spread.12-14 While the relationships among climate conditions, water quality, and related diseases have been documented in developed regions,15-17 there is little study in such relationships in the MDB. This review’s objective is to support further climate change–related research efforts and adaptation strategies in MDB by seeking answers to the following 2 questions:
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Phung et al Table 1. Keywords and Terms Used in the Searching Process. (1) (2)
(3) Searching strategy
“heatwaves” OR “drought” OR “bushfires” OR “flooding” OR “storms” OR “tropical” OR “cyclones” “water quality” OR “waterborne diseases” OR “water-related diseases” OR “water-based diseases” OR “gastro-intestinal diseases” OR “diarrhoea” OR “abdominal discomfort” OR “intestinal disturbance” OR “malnutrition” OR “Legionellosis” OR “cholera” OR “E. coli infection” OR “Leptospirosis” OR “Salmonellosis” OR “Typhoid fever” OR “schistosomiasis” OR “Vibrio Illness” OR “Adenovirus infection” OR “Gastroenteritis” OR “Hepatitis A” OR “Polyomavirus infection” OR “malaria” OR “Filariasis” OR “Sleeping sickness” OR “dysenteries” OR “arsenics” OR “pesticides” OR “metals” OR “drowning” OR “injury” OR “guinea-worm diseases” OR “Japanese Encephalitis” OR “Lead Poisoning” OR “Scabies” OR “Onchocerciasis” OR “Methaemoglobinemia” OR “impetigo” OR “conjunctivitis” OR “scrub typhus” OR “shigellosis” OR “dengue fever” OR “amoebiasis” OR “infection” OR “famine” “China” OR “Vietnam” OR “Cambodia” OR “Lao” OR “Myanmar” OR “Burma” OR “Thai Land” (1) AND (2) AND (3) Limit “English full-text”
•• How are water quality and related diseases associated with changes in climate conditions in the MDB? •• What are the recommendations for further research to fill the gaps of knowledge on the relationships between climate conditions, water quality, and water-related diseases in the MDB?
Methods Study Selection The information sources for literature search included PubMed, Proquest, CINAHL-EBSCO, GoogleScholar, and references from relevant literature. We created 3 categories of keywords by using “OR” within a group and combined them by using “AND” between groups. The 3 categories comprised the following: (a) climate-related conditions—temperature, heatwaves, rainfall, flood, sea level rise, drought, bushfire, storm, tropical cyclone; (b) outcomes—water quality, waterborne disease, vector-borne disease; and (c) settings—Mekong Delta, China, Cambodia, Laos, Myanmar, Burma, Thailand, and Vietnam. Our search was limited to full-text publications in English. The keywords are listed in Table 1. The eligible criteria comprised the following: (a) published reports where explicit link was made between climate conditions and water quality and/or water-related diseases, (b) research settings were in any part of MDB, and (c) research was not limited by study design and date. The exclusion criteria included (a) published articles with only English abstracts and (b) reports that are not from research projects (eg, magazine’s news). The screening of potentially eligible studies was carried out through 3 sequential steps, including title, abstract, and full-text review against inclusion and exclusion criteria (Figure 2). Duplicated articles from different sources were excluded at the abstract review step. Additional articles were identified using manual searching from the references at the full-text review step. As climate change is a natural phenomenon, the impacts of which cannot be tested experimentally, research quality assessment was not possible for each study.
Data Collection and Analysis Data from articles were extracted (Table 2), including: author/year, country, design, climate factors, and outcomes. Given the varied nature of studies and outcomes, both quantitative and qualitative findings were included in the outcome summary. The data analyses include summary on evidence of Downloaded from aph.sagepub.com at Purdue University on June 12, 2015
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Records idenfied through database 1510 1810 11 150 9 2490
PubMed Proquest CINAHL Googlescholar Other sources Total
1st screening: Title review(n=2389)
101
Records selected for candidate abstracts
Non-relevant tles Not scien fic research (e.g. news) Exclusion criteria Duplicates
Exclusion of double records (n=17)
Records selected for abstract reviews
84
2nd screening - Abstract review (n=40) Records selected for full text reviews and author contact
45
No climate change related condi ons (n=28) Not in Mekong Delta/ or Mekong Delta separated (n=9) Double research project (n=3)
3rd screening – Full text review (n=16)
13
Records included
No climate condi ons (n=4) Climate condi ons only (n=16) Not Mekong Delta separated (n=8) Adapta on study (n=2) Duplicate (n=2)
Figure 2. Flowchart for inclusion and exclusion of studies.
the relationship between climate conditions and water quality and/or water-related diseases, identified limitations and gaps. For the climate-outcome relationships that were not quantitatively evaluated, a qualitative content based analysis was applied to identify frequent quotes. A critical analysis of individual studies was also conducted to determine the gaps and recommend further studies.
Results Study Characteristics Our search strategy identified 2490 potential articles. The first screening of title excluded 2389 reports. Primary reasons for exclusion were nonrelevant titles, nonscientific studies, and meeting Downloaded from aph.sagepub.com at Purdue University on June 12, 2015
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Phung et al Table 2. Summary of Included Studies. Author(s)/Year
Country
Research Method
Few and Tran (2010)20
Vietnam
Qualitative study
Kelly-Hope et al (2007)18 and (2008)19 Nguyen (2008) Few et al (2013)21
Vietnam
Ecological cross-sectional study Review Cross-sectional and qualitative study
Victoriano et al (2009)22 Isobe et al (2004)23
Multi-countries
Review
Vietnam
Kien et al (2010)
Vietnam
Time-series environmental monitoring Time-series and spatial analysis
CNREM–DONRE (2009)25
Vietnam
Environmental monitoring
Birkmann et al (2010)26 Few et al (2004)27
Vietnam
Prathumratana et al (2008)29
Multiple countries
Vulnerability assessment Cross-sectional survey Environmental monitoring
Ellis et al (2012)28
Multiple countries
Environmental monitoring
Vietnam Vietnam
Vietnam
Climate Change– Related Condition
Water Quality/WaterRelated Disease
Flood interacts with other social and individual factors Rainfalls, vapor pressure
Water-related injury and diseases (self-reports) Shigellosis, typhoid fever
Flood Dry
Mortality Increase of E coli counts in water; however, low rate of diarrhea during dry season phase Leptospirosis disease
Rainy season and floods Wet, dry, and water temperature Rainfall and flood
Temperature, humidity, precipitation, and others Flood Flood Precipitation, evaporation, average air temperatures, mean water level and discharge flow Flood and drought
Coprostanol, E coli, and fecal streptococcus Waterborne diseases: cholera, dysentery, typhoid fever, and diarrheal diseases Water quality (10 parameters + coliform) Mortality Injury and waterborne diseases Water quality parameters
Change in particulate organic matter
the exclusion criteria. After excluding duplicated studies, 84 articles were selected for further abstract evaluation. The second screening left 45 articles as full-text review candidates. Common reasons for exclusion at this stage were no climate conditions, the Mekong Delta not being the setting of the study, and duplicated studies. The third screening based on full-text review resulted in 13 articles remaining. The reasons for the article exclusion in the third screening are shown in Figure 2. The multiplier effects of climate conditions on water quality and health were reported in 13 studies.5,18-29 The study approaches used to examine the relationship between climate conditions and water quality/diseases included ecological and time-series study, environmental monitoring, qualitative study, vulnerability assessment, and reviews. The study locations can be categorized as multi-country if 2 or more MDB countries were involved and single-country if only one country was involved. Downloaded from aph.sagepub.com at Purdue University on June 12, 2015
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Results of Association Between Climate Conditions and Water Quality Most of included studies provided strong qualitative emphasis on the impacts of climate change on water quality. These emphases are drawn from the reviews on climate change–related extreme episodes, future projected climate conditions, and evidence from studies in other regions but not the MDB. Therefore, the most common phrase “. . . is likely . . .” is used to emphasize the effects of climate change to water quality. This reflects the uncertainty and inconclusive findings of these studies. The frequent outcomes emphasized in the studies comprise “salinity,” “chemical contamination,” “hygienic condition,” “pathogen contamination,” “nutrient cycling,” and “algal blooms.” The most common concern was increased salinization of groundwater supplies in the majority of areas in MDB due to sea water intrusion.4,30-32 High salinity due to saltwater intrusion was believed to be common in delta tributaries and channels, and there is significant difference in salinity levels between the dry and rainy seasons.33 In addition, the reduction of stream-flows was also believed to increase the salinity of waterways.34,35 Chemical contamination was identified as being worsen due to the variability of climate change. The potential contaminants included heavy metals, pesticides, and toxic algae. It was emphasized that pesticides were likely to increase in usage and contamination due to the changes of climate. For example, high-intensity rainfall may lead to increase in more application of pesticides, resulting in elevation of these substances to surface waters.31 The studies by vastila et al3 and Lambert36 indicated that the higher and longer flooding might enhance cycling of nutrients and organic matter between the floodplain and the permanent water bodies, which may result in increased concentrations of nutrients that promote algal blooms. This will cause increased pathogens and impact ecosystems and human health. However, no study has investigated the relationship between climate factors and proliferation of algae and its adverse health effects. Though the qualitative studies emphasized emerging impacts of climate change on water quality, only a few studies quantified relationship between climate factors and water quality parameters. A multi-country study29 found significant correlations between hydrometeorological factors and some water quality parameters in the lower MDB (Thailand, Cambodia, Lao PDR, and Vietnam). A positive correlation was reported for air temperature with total suspended solids, NO3− , PO3− 4 . and chemical oxygen demand; whereas dissolved oxygen, pH, conductivity, Ca, Mg, Na, K, alkalinity, Cl, SO 2− 4 , and Si were negatively correlated with hydrological factors. However, this study did not examine the link to microbiological parameters. Regarding pathogen contamination, the number of Escherichia coli was found higher in the wet season than the dry season.23 In contrast, a study conducted in the same area21 reported lower E coli concentrations in the October, the flood season, than that in April 2008, the dry season. The other study21 expressed that although the pathogens was significant associated with seasonality, there was no consistent evidence in this association. These inconclusive findings may be attributed to fact that the studies did not consider multivariate climate factors (eg, air temperature, rainfall, and humidity) in the analysis. These factors can cause changes in development of microbiological pathogens. Some change in water quality over time were quantified in some studies conducted in the Vietnam Mekong Delta,25,33 and the findings implied these changes were caused by the changes in climate conditions. The results showed that pH and nitrate remained within permissible levels, while all other parameters such as coliforms, suspended solids, phosphates, and ammonia exceeded the guideline levels set by national regulations. These studies suggest that these issues are related to climate change; however, no evidence in this relationship has been evaluated. In terms of knowledge gaps, the studies indicated that there was a big gap of knowledge on the impacts of climate change to water quality, especially to groundwater in the Mekong Delta region.4,32,33 For instance, the interaction between surface and ground water during a flooding
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event has not been investigated, resulting in a large gap of information required for developing adaptation strategies in the MDB. The study4 also indicated that it is necessary to more assess impacts of climate change on the groundwater resources in various parts of the MDB.
Results of Association Between Climate Conditions and Water-Related Diseases Waterborne Diseases. A few single-country studies were conducted in the Vietnam Mekong Delta. Increased diarrheal visits following flooding events were commonly reported in some studies,21,27,37,38 and diarrhea was considered to be of most concern for inhabitants living in Mekong Delta. Diarrhea was associated with disruption to normal water/sanitation services and the spreading of contamination due to flooding events, which can contaminate drinking water sources and inundate latrines, spreading pathogens in the environment. However, these studies had some limitations. First, data on diarrhea were obtained from interviews with inhabitants, so the results might be biased due to recall error of interviewees. Second, these studies did not examine the seasonal and spatial pattern of diarrhea corresponding to flood duration, intensified levels, and flood time. Such information could assist in better health preparedness of local health departments. Finally, these studies did not consider climate factors in analyzing the flooddiarrhea relationship. Very limited information about the groundwater resource size, use sustainability and quality is available from the literature. Only a few studies exist, focusing on some local areas within the Mekong Basin exist where they have made an assessment of resource, use and/or quality. Therefore, little can be said about potential climate change impacts. (Eastham et al, 2008)4(p59)
Some studies investigated the relationship between climate factors and cause-specific diarrhea in Vietnam Mekong Delta. The study conducted by Kien et al24 in 2005 indicated that increased rates of typhoid fever was associated with increase in annual floods, and the disease outbreaks were significantly correlated with temperature but not rainfall. Nevertheless, the timeseries were not properly designed to evaluate a short-term relationship between climate factors and the disease. The study by Kelly-Hope et al19 found that bacterial enteric diseases have distinct temporal and seasonal patterns, in which climate plays a role in defining high- and lowdisease period; however, climate factors did not appear to affect outbreaks. In another study, Kelly-Hope et al18 expressed that typhoid fever prevailed in the Mekong Delta and was mostly associated with vapor pressure and river/stream drinking water quality. The peak period of typhoid fever usually occurred prior to the rainy season, when river levels were low. Hence the epidemics are likely associated with scarcity of water and compromised hygiene practices.39-41 However, no study has investigated the influence of climate factors such as temperature, rainfall, and humidity on the patterns of this disease. Water-Related Mosquito-Borne Diseases. Malaria and dengue fever threaten to reemerge in the Vietnam Mekong Delta due to the changes in climate factors on the breeding of mosquito larvae.27 It was suggested that incidence of dengue fever be commonly increased in the flood season because people probably more relied on treating and storing river water in containers. The study24 indicated that the number of reported malaria cases peaked from October through January (during and after the rainy season), and most of the peaks of malaria occurred during disaster events in El Nino years. Nevertheless, this study did not examine the short-term patterns of malaria in relation to climate factors such as temperature, humidity, and rainfall. Other Water-Related Diseases. Leptospirosis and influenza were found to associate with climate factors in a few studies.22,24 Kien et al24 mentioned that in the Mekong Delta, increased influenza
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was associated with a lower mean temperature and higher humidity; meanwhile, the disease had the highest rates during the period of August to October. A multi-country study22 indicated that Vietnam, Cambodia, and Laos have been considered endemic for leptospirosis, and the outbreaks of this disease associated with rainfall. However, these studies did not quantify the relationship between the diseases and climate factors over time and locations. Studies on effects of climate factors on other water-related diseases such as fungal skin disease, eye infections, gynecological infections, which are caused by other types of water contaminants such as arsenic, pesticides, toxic algae, and industrial chemicals, have not been conducted anywhere else in the Mekong Delta.
Discussion The review indicated that a few studies provided preliminary evidences of association between hydroclimate factors and water quality; however, these evidences are not sufficient to evaluate the influence of variation in climate factors on water quality parameters as reported somewhere else. For instance, the study conducted by Harper et al12 in Canada found that weekly water volume input was positively associated with untreated water coliform levels and related to the gastrointestinal illness admitted into hospitals, and higher water temperatures will probably result in a higher pathogen survival in the environment.42 Besides the basic water quality parameters, studies in association between climate factors and chemicals contamination (eg, metals, pesticides) have been neglected in the MDB. The study indicated that climate change would influence on the fate and transport of chemical contaminants in agricultural systems.43 Increases in temperature and alteration in moisture characteristics may reduce the persistence of chemicals while changes in hydrologic characteristics can result in increasing the potential for contaminants to be transported to water supplies. For example, global warming is likely to reduce soil and aquatic concentrations of pesticides due to combination of elevated volatilization and degradation,44,45 whereas increases in the intensity and frequency of rain and storm events will increase the wet deposition of pesticides to aquatic systems.46,47 Climate change also changes the frequency and amount of pesticides used as agriculture shifts corresponding to the rapidly changing climate48; as a consequence, this will spread out the pesticide contamination due to runoff during the high rainy season. The potential adverse health effects caused by agricultural pesticide exposure can be a wide range of signs, symptoms, and diseases, including reduced eye-hand coordination, effects on cognitive abilities, developmental toxicity, estrogenic effects, antiandrogenic effects, congenital abnormalities, reduced stamina, pregnancy loss, and Parkinson’s disease.43 Most of studies indicated that increases in waterborne and vector-borne diseases associated with flooding events in the MDB; however, these study designs just focused on extreme events but not on annual variability of hydrometeorological conditions (eg, annual flood pulse). It is believed that regular short-term climate variability will still continue to cause problems for water and water-related health effects.30 Therefore, the effects of both unusual extreme events relating to long-term climate change and “normal” variability of climate need to be considered extensively in the MDB. Although the plausible mechanism underlying the present association between hydrometeorological factors and water-related diseases is unclear, there are several possible etiologic and meteorologic explanations. The reason for rainfall disease outbreaks is the change in the direction of flow of water systems and flow through channels that would not normally occur, resulting in substantial amounts of fecal polluted water into rivers, and this may be worsen in areas where sanitation services are insufficient and agricultural activities are located within catchments. Rainfall-related flood events were also found to be associated with other infectious diseases such as leptospirosis,49,50 hepatitis E, malaria,51,52 and acute respiratory disease.53
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The link between increased temperature and waterborne disease were possibly because of the blooms of various planktonic species. For example, cyanobacteria (blue-green algae) was found to be associated with dermatitis, respiratory problems and hepatitis,54 and dinoflagellates and diatoms can cause neurotoxicity and shellfish poisonings.55 One of the most clear effects of temperature on risk of waterborne disease relates to cholera,56 and this is attributed to the increased temperature-plankton bloom, resulting in increased cholera as it survives more with algae and plankton. Variability in temperature was also found to be associated with the risk of vector-borne disease because it can affect both the distribution of the vector and the effectiveness of pathogen transmission through the vector.57,58 The possible mechanisms for this relationship are increasing or decreasing survival of vector, changes in rate of vector population growth, feeding behavior, susceptibility of vector to pathogens, incubation period of the pathogen, seasonality of vector activity, and seasonality of pathogen transmission.59 Nevertheless, these relationships have been poorly investigated in the MDB. This current review has some limitations. The terms underinvestigated, underrecognized, and underreported might be seen in this review for several reasons. First, most of the health effects of climate changes are indirect, so it is difficult to identify climate change as the sole exposure factor responsible for a given health outcome. Second, in most developing areas, such as the MDB, research in climate change and health is in its infancy, so it is difficult to find high-quality and long-term research on this issue. Moreover, the articles included in this review are diverse, either project reports or research articles, so they have widely varying study designs, leading to variation in quality. However, because of the shortage of articles, all available articles that presented climate factors, water quality, and water-related diseases in the MDB were included for review. Information bias from included articles as extreme climate change is more likely reported, and the evidence borrowed from other locations in the world may be not applicable to the MDB.
Conclusion and Recommendations This systematic review provides a summary of the evidence on the association between climate factors, water quality, and water-related diseases in the MDB. Based on limitations and gaps of the existing studies, the review also provides some useful recommendations to support health sectors and international agencies in efforts to plan for further research, policy development, and adaptation strategies in the MDB. Although this review represents an initial attempt at summarizing the available evidence on the climate factors, water quality, and water-related diseases in the MDB, a number of recommendations for further research are provided below: •• In terms of water quality associated with climate factors, studies with more sensitive analysis are required to examine the short-term association between climate conditions and water quality parameters. Research on the relationship between climate conditions and salinity, chemical contamination, and pathogen contamination in both river water and groundwater supply should be further conducted to fill the gaps of knowledge and information. •• In terms of water related diseases in relation to climate factors, understanding of the pattern of diseases during and after a flooding event would be useful for public health preparedness and prevention. The variation of water-related diseases caused by an annual flood pulse, which is also of interest for regular preparedness and control in local health departments, should be investigated. The influence of other climate factors such as temperature, rainfall, and humidity need to be taken into account as potential exposure factors in climate-disease relationship in MDB. Other health issues such as dermatitis, respiratory illness and hepatitis and those potentially caused by cyanobacteria (blue-green algae) should also be considered in any comprehensive examination in climate-disease association.
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Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
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21. Few R, Lake I, Hunter PR, Tran PG, Seasonality, disease and behaviour: using multiple methods to explore socio-environmental health risks in the Mekong Delta. Soc Sci Med. 2013;80:1-9. 22. Victoriano AF, Smythe LD, Gloriani-Barzaga N, et al. Leptospirosis in the Asia Pacific region. BMC Infect Dis. 2009;9:1-9. 23. Isobe KO, Tarao M, Nguyen HC, Le YM, Takada H. Effect of environment factors on the relationship between concentrations of coprostanol and fecal indicato bacteria in tropical (Mekong Delta) and temperate (Tokyo) freshwaters. Appl Environ Microbiol. 2004;70:814-821. 24. Kien TM, Tran TTH, Cuong HD, Shaw R. Identifying linkages between rates and distributions of malaria, water-borne diseases and influenza with climate variability and climate change in Vietnam. In: Shaw R, Pulhin JM, Pereira JJ, eds. Climate Change Adaptation and Disaster Risk Reduction: An Asian Perspective. Bingley, England: Emerald, UK; 2010:417-449. 25. Can Tho DONRE. Report on Environment Quality Monitoring: Can Tho City 10 years (1999-2008). Can Tho, Vietnam: Center of Natural Resources and Environment Monitoring (CNREM), Can Tho Department of Natural Resources and Environment (DONRE); 2009. 26. Birkmann J, Garchagen M, Tuan VV, Binh NT. Vulnerability profiles with respect to present and future water related hazards in the Vietnamese Mekong Delta—providing the information-base for successful coping and adaptation within the framework of integrated water resources management. 2010. http:// www.wisdom.caf.dlr.de/sites/wisdom/files/images/results/101007_wisdom-va-proifles_new_map_ compressed_names_new.pdf. Accessed December 10, 2014. 27. Few R, Pham TG, Bui HTT. Living with floods: health risk and coping strategies of the urban poor in Vietnam. Committee for South East Asian Studies. Project reported 2004. 2004. 28. Ellis EE, Keil RG, Ingalls AE, Richey JE, Alin SR, Seasonality variability in the sources of particulate organic matter of the Mekong River as discerned by elemental and lignin analyses. J Geophys Res. 2012;117:1-15. 29. Prathumratana L, Sthinnopkao S, Kim KW. The relationship of climatic and hydrological parameters to surface water quality in the lower Mekong River. Environ Int. 2008;34:860-866. 30. Jacobs JW. Adjusting to climate change in the Lower Mekong. Global Environ Change. 1995;6:7-22. 31. Water Environment Research Foundation. Implications of Climate Change for Adaptation by Wastewater and Stormwater Agencies. Boulder, CO: Stratus Consulting; 2008. 32. Snidvongs A, Choowaew S, Chinvanno S. Impact of climate change on water and wetland resources in Mekong River Basin: directions for preparedness and action (Southeast Asia START Regional Center Report Number 12). 2003. 33. Neumann L, Nguyen M, Moglia M, Cook S, Lipkin F. Urban water systems in Can Tho, Vietnam: understanding the current context for climate change adaptation. 2013. https://publications.csiro.au/rpr/ download?pid=csiro:EP115086&dsid=DS12013. Accessed December 10, 2014. 34. Dragon Institute. Climate Change Impacts and Vulnerabilities Assessment for Can Tho City. Can Tho, Vietnam: Asia Cities Climate Change Resilience Network Program. 2009. 35. Khang ND, Kotera A, Sakamoto T, Yokozawa M. Sensitivity of salinity intrusion to sea level rise and river flow change in Vietnamese Mekong Delta—impacts on availability of irrigation water for rice cropping. J Agric Meteorol. 2008;64:167-176. 36. Lambert D. Little impact, much damage: the consequences of Mekong River flow alterations for the Tonle Sap ecosystem. In: Kummu M, Keskinen M, Varis O, eds. Modern Myths of the Mekong. A Critical Review of Water and Development Concepts, Principles and Policies. Helsinki, Finland: Water and Development Publications, Helsinki University of Technology; 2008:3-18. 37. Nguyen HN. Fighting climate change: human solidarity in a divided world. Flooding in Mekong River Delta, Vietnam. UNDP Human Development Report 2007/2008, 2008. 38. Moglia M, Neumann LE, Alexander KS, et al. Application of the Water Needs Index: Can Tho City, Mekong Delta, Vietnam. J Hydrol. 2012;468-469:203-212. 39. Lin FY, Vo AH, Phan VB, et al. The epidemiology of typhoid fever in the Dong Thap Province, Mekong Delta region of Vietnam. Am J Trop Med Hyg. 2000;62:644-648. 40. Nguyen TA, Ha Ba K, Nguyen TD. Typhoid fever in South Vietnam, 1990-1993 [in French]. Bull Soc Pathol Exot. 1993;86(5 pt 2):476-478. 41. Luxemburger C, Chau MC, Mai NL, et al. Risk factors for typhoid fever in the Mekong Delta, southern Vietnam: a case-control study. Trans R Soc Trop Med Hyg. 2001;95:19-23.
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42. Hunter PR. Climate change and waterborne and vector-borne disease. J Appl Microbiol. 2003;94(suppl):37S-46S. 43. Boxall ABA, Hardy A, Beulke S, et al. Impacts of climate change on indirect human exposure to pathogens and chemical from agriculture. Environ Health Perspect. 2009;117:508-514. 44. Bailey SW. Climate change and decreasing herbicide persistence. Pest Manag Sci. 2004;60:158-162. 45. Benitez FJ, Real FJ, Acero JL, Garcia C. Photochemical oxidation process for the elimination of phenyl-urea herbicides in waters. J Hazard Mater. 2006;138:278-287. 46. Bollmohr S, Day JA, Schulz R. Temporal variability in particle-associated pesticide exposure in a temporarily open estuary, Western Cape, South Africa. Chemosphere. 2007;68:479-488. 47. Bloomfield JP, William RJ, Gooddy DC, Cape JN, Guha P. Impacts of climate change on the fate and behaviour of pesticides in surface and groundwater—a UK perspective. Sci Total Environ. 2006;369:163-177. 48. Chen CSQ, McCarl BA. An investigation of the relationship between pesticide usage and climate change. Climatic Change. 2001;50:475-487. 49. Barcellos C, Sabrosa PC. The place behind the case: leptospirosis risks and associated environmental condition in a flood-related outbreak in Rio de Janeiro. Cadernos Saude Publica. 2001;17(suppl): 59-67. 50. Easton A. Leptospirosis in Philippine floods. BMJ. 1999;319:212. 51. Shears P. The Khartoum floods and diarrhoeal diseases. Lancet. 1988;2:517. 52. McCarthy MC, He J, Hyams KC, et al. Acute hepatitis E infection during the 1988 floods in Khartoum, Sudan. Trans R Soc Trop Med Hyg. 1994;88:177. 53. Campanella N. Infectious disease and natural disasters: the effects of Hurricane Mitch over Villanueva municipal area, Nicaragua. Public Health Rev. 1999;27:311-319. 54. Hunter PR. Cyanobacterial toxins and human health. J Appl Bacteriol. 1998;84(suppl):35S-40S. 55. Hungerford JM. Seafood toxins. In: Labbe RG, Garcia S, eds. Guide to Foodborne Pathogens. New York, NY: Wiley; 2001:267-283. 56. Cowel RR. Global climate change and infectious disease: the cholera paradigm. Science. 1996;274: 2025-2031. 57. Bouma MJ, Dye C, Van der Kaay HJ. Falciparum malaria and climate change in the North West Frontier Province of Pakistan. Am J Trop Med Hyg. 1996;55:131-137. 58. Cannell MGR, Palutokof JP, Sparks TH. Indicators of Climate Changes in the UK. London, England: Department of the Environment, Transport and the Regions; 1999. 59. Gubler DJ, Reiter P, Ebi KL, et al. Climate change variability and change in the United States: potential impacts on vector- and rodent-borne diseases. Environ Health Perspect. 2001;109(suppl 2):223-233.
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APHXXX10.1177/1010539514565448Asia-Pacific Journal of Public HealthPhung et al
Review Article
Climate Change, Water Quality, and Water-Related Diseases in the Mekong Delta Basin: A Systematic Review
Asia-Pacific Journal of Public Health 2015, Vol. 27(3) 265–276 © 2015 APJPH Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/1010539514565448 aph.sagepub.com
Dung Phung, PhD1, Cunrui Huang, PhD1, Shannon Rutherford, PhD1, Cordia Chu, PhD1, Xiaoming Wang, PhD2, and Minh Nguyen, DrEng2
Abstract Mekong Delta Basin (MDB) is vulnerable to extreme climate and hydrological events. The objectives of this review are to understand of water related health effects exacerbated by climate change and the gaps of knowledge on the relationships between climate conditions, water quality, and water-related diseases in the MDB. The findings indicate that a few studies with qualitative emphases on the relationships between climate and water quality have been conducted in MDB, and they are insufficient to describe the pattern of climate-disease relationship. The diseases caused by chemical contaminants in relation to changes of climate conditions are neglected in MDB. We suggest further studies to examine the influence of short-term variation of climate conditions on water quality and water-related diseases for the purpose of public health and medical prevention, and due to the trans-boundary nature of MDB, developing partnership in data sharing and research collaboration among MDBs countries should be prioritized. Keywords climate change, water quality, water-related diseases, Mekong Delta Basin, Mekong Delta River
Introduction The Mekong Delta Basin (MDB; Figure 1) is vulnerable to extreme climate and hydrological events.1 The air temperature in the MDB is predicted to increase a few degrees Celsius in the period from 2030 to 2100.2 The sea level in the MDB could rise up to 1 m by the 2100s.3 A wide variation in rainfall is projected across the MDB.2-5 Flood duration has been suggested to increase
1Griffith
University, Nathan Campus, Brisbane, Queensland, Australia Scientific and Industrial Research Organization (CSIRO), Canberra, Australia
2Commonwealth
Corresponding Authors: Dung Phung, Centre for Environment and Population Health, Griffith School of Environment, Griffith University, Nathan campus, 179 Kessels Road, Nathan, Brisbane, Queensland 4111, Australia. Email: [email protected] Cunrui Huang, School of Public Health, Sun Yat-sen University, 74 Zhongshan Road #2, Guangzhou, Guangdong Province 510080, China. Email: [email protected]
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Figure 1. Mekong Delta Basin (Source: Eastham et al, 2008).4
in all the simulated scenarios.3 Besides the annual flood pulse, increasing likelihood of extreme floods was predicted.4,6 Droughts were also predicted to be more intensified in MDB.4 Changes of climate can negatively affect water quality in river basin7 because they cause alteration in the pattern and distribution of rainfall over the entire basin, leading to changes in river flow volume, leading to changes in the transport of biological pathogens.8,9 The long drought periods have also negative effects on water quality such as temperature, dissolved oxygen, biochemical oxygen demand, and concentration of pathogens and certain chemical compounds.10,11 As a consequence, these climate changes are considered to contribute to elevating the risk of waterborne diseases due to the variation of pathogen concentration and spread.12-14 While the relationships among climate conditions, water quality, and related diseases have been documented in developed regions,15-17 there is little study in such relationships in the MDB. This review’s objective is to support further climate change–related research efforts and adaptation strategies in MDB by seeking answers to the following 2 questions:
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(3) Searching strategy
“heatwaves” OR “drought” OR “bushfires” OR “flooding” OR “storms” OR “tropical” OR “cyclones” “water quality” OR “waterborne diseases” OR “water-related diseases” OR “water-based diseases” OR “gastro-intestinal diseases” OR “diarrhoea” OR “abdominal discomfort” OR “intestinal disturbance” OR “malnutrition” OR “Legionellosis” OR “cholera” OR “E. coli infection” OR “Leptospirosis” OR “Salmonellosis” OR “Typhoid fever” OR “schistosomiasis” OR “Vibrio Illness” OR “Adenovirus infection” OR “Gastroenteritis” OR “Hepatitis A” OR “Polyomavirus infection” OR “malaria” OR “Filariasis” OR “Sleeping sickness” OR “dysenteries” OR “arsenics” OR “pesticides” OR “metals” OR “drowning” OR “injury” OR “guinea-worm diseases” OR “Japanese Encephalitis” OR “Lead Poisoning” OR “Scabies” OR “Onchocerciasis” OR “Methaemoglobinemia” OR “impetigo” OR “conjunctivitis” OR “scrub typhus” OR “shigellosis” OR “dengue fever” OR “amoebiasis” OR “infection” OR “famine” “China” OR “Vietnam” OR “Cambodia” OR “Lao” OR “Myanmar” OR “Burma” OR “Thai Land” (1) AND (2) AND (3) Limit “English full-text”
•• How are water quality and related diseases associated with changes in climate conditions in the MDB? •• What are the recommendations for further research to fill the gaps of knowledge on the relationships between climate conditions, water quality, and water-related diseases in the MDB?
Methods Study Selection The information sources for literature search included PubMed, Proquest, CINAHL-EBSCO, GoogleScholar, and references from relevant literature. We created 3 categories of keywords by using “OR” within a group and combined them by using “AND” between groups. The 3 categories comprised the following: (a) climate-related conditions—temperature, heatwaves, rainfall, flood, sea level rise, drought, bushfire, storm, tropical cyclone; (b) outcomes—water quality, waterborne disease, vector-borne disease; and (c) settings—Mekong Delta, China, Cambodia, Laos, Myanmar, Burma, Thailand, and Vietnam. Our search was limited to full-text publications in English. The keywords are listed in Table 1. The eligible criteria comprised the following: (a) published reports where explicit link was made between climate conditions and water quality and/or water-related diseases, (b) research settings were in any part of MDB, and (c) research was not limited by study design and date. The exclusion criteria included (a) published articles with only English abstracts and (b) reports that are not from research projects (eg, magazine’s news). The screening of potentially eligible studies was carried out through 3 sequential steps, including title, abstract, and full-text review against inclusion and exclusion criteria (Figure 2). Duplicated articles from different sources were excluded at the abstract review step. Additional articles were identified using manual searching from the references at the full-text review step. As climate change is a natural phenomenon, the impacts of which cannot be tested experimentally, research quality assessment was not possible for each study.
Data Collection and Analysis Data from articles were extracted (Table 2), including: author/year, country, design, climate factors, and outcomes. Given the varied nature of studies and outcomes, both quantitative and qualitative findings were included in the outcome summary. The data analyses include summary on evidence of Downloaded from aph.sagepub.com at Purdue University on June 12, 2015
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Records idenfied through database 1510 1810 11 150 9 2490
PubMed Proquest CINAHL Googlescholar Other sources Total
1st screening: Title review(n=2389)
101
Records selected for candidate abstracts
Non-relevant tles Not scien fic research (e.g. news) Exclusion criteria Duplicates
Exclusion of double records (n=17)
Records selected for abstract reviews
84
2nd screening - Abstract review (n=40) Records selected for full text reviews and author contact
45
No climate change related condi ons (n=28) Not in Mekong Delta/ or Mekong Delta separated (n=9) Double research project (n=3)
3rd screening – Full text review (n=16)
13
Records included
No climate condi ons (n=4) Climate condi ons only (n=16) Not Mekong Delta separated (n=8) Adapta on study (n=2) Duplicate (n=2)
Figure 2. Flowchart for inclusion and exclusion of studies.
the relationship between climate conditions and water quality and/or water-related diseases, identified limitations and gaps. For the climate-outcome relationships that were not quantitatively evaluated, a qualitative content based analysis was applied to identify frequent quotes. A critical analysis of individual studies was also conducted to determine the gaps and recommend further studies.
Results Study Characteristics Our search strategy identified 2490 potential articles. The first screening of title excluded 2389 reports. Primary reasons for exclusion were nonrelevant titles, nonscientific studies, and meeting Downloaded from aph.sagepub.com at Purdue University on June 12, 2015
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Phung et al Table 2. Summary of Included Studies. Author(s)/Year
Country
Research Method
Few and Tran (2010)20
Vietnam
Qualitative study
Kelly-Hope et al (2007)18 and (2008)19 Nguyen (2008) Few et al (2013)21
Vietnam
Ecological cross-sectional study Review Cross-sectional and qualitative study
Victoriano et al (2009)22 Isobe et al (2004)23
Multi-countries
Review
Vietnam
Kien et al (2010)
Vietnam
Time-series environmental monitoring Time-series and spatial analysis
CNREM–DONRE (2009)25
Vietnam
Environmental monitoring
Birkmann et al (2010)26 Few et al (2004)27
Vietnam
Prathumratana et al (2008)29
Multiple countries
Vulnerability assessment Cross-sectional survey Environmental monitoring
Ellis et al (2012)28
Multiple countries
Environmental monitoring
Vietnam Vietnam
Vietnam
Climate Change– Related Condition
Water Quality/WaterRelated Disease
Flood interacts with other social and individual factors Rainfalls, vapor pressure
Water-related injury and diseases (self-reports) Shigellosis, typhoid fever
Flood Dry
Mortality Increase of E coli counts in water; however, low rate of diarrhea during dry season phase Leptospirosis disease
Rainy season and floods Wet, dry, and water temperature Rainfall and flood
Temperature, humidity, precipitation, and others Flood Flood Precipitation, evaporation, average air temperatures, mean water level and discharge flow Flood and drought
Coprostanol, E coli, and fecal streptococcus Waterborne diseases: cholera, dysentery, typhoid fever, and diarrheal diseases Water quality (10 parameters + coliform) Mortality Injury and waterborne diseases Water quality parameters
Change in particulate organic matter
the exclusion criteria. After excluding duplicated studies, 84 articles were selected for further abstract evaluation. The second screening left 45 articles as full-text review candidates. Common reasons for exclusion at this stage were no climate conditions, the Mekong Delta not being the setting of the study, and duplicated studies. The third screening based on full-text review resulted in 13 articles remaining. The reasons for the article exclusion in the third screening are shown in Figure 2. The multiplier effects of climate conditions on water quality and health were reported in 13 studies.5,18-29 The study approaches used to examine the relationship between climate conditions and water quality/diseases included ecological and time-series study, environmental monitoring, qualitative study, vulnerability assessment, and reviews. The study locations can be categorized as multi-country if 2 or more MDB countries were involved and single-country if only one country was involved. Downloaded from aph.sagepub.com at Purdue University on June 12, 2015
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Results of Association Between Climate Conditions and Water Quality Most of included studies provided strong qualitative emphasis on the impacts of climate change on water quality. These emphases are drawn from the reviews on climate change–related extreme episodes, future projected climate conditions, and evidence from studies in other regions but not the MDB. Therefore, the most common phrase “. . . is likely . . .” is used to emphasize the effects of climate change to water quality. This reflects the uncertainty and inconclusive findings of these studies. The frequent outcomes emphasized in the studies comprise “salinity,” “chemical contamination,” “hygienic condition,” “pathogen contamination,” “nutrient cycling,” and “algal blooms.” The most common concern was increased salinization of groundwater supplies in the majority of areas in MDB due to sea water intrusion.4,30-32 High salinity due to saltwater intrusion was believed to be common in delta tributaries and channels, and there is significant difference in salinity levels between the dry and rainy seasons.33 In addition, the reduction of stream-flows was also believed to increase the salinity of waterways.34,35 Chemical contamination was identified as being worsen due to the variability of climate change. The potential contaminants included heavy metals, pesticides, and toxic algae. It was emphasized that pesticides were likely to increase in usage and contamination due to the changes of climate. For example, high-intensity rainfall may lead to increase in more application of pesticides, resulting in elevation of these substances to surface waters.31 The studies by vastila et al3 and Lambert36 indicated that the higher and longer flooding might enhance cycling of nutrients and organic matter between the floodplain and the permanent water bodies, which may result in increased concentrations of nutrients that promote algal blooms. This will cause increased pathogens and impact ecosystems and human health. However, no study has investigated the relationship between climate factors and proliferation of algae and its adverse health effects. Though the qualitative studies emphasized emerging impacts of climate change on water quality, only a few studies quantified relationship between climate factors and water quality parameters. A multi-country study29 found significant correlations between hydrometeorological factors and some water quality parameters in the lower MDB (Thailand, Cambodia, Lao PDR, and Vietnam). A positive correlation was reported for air temperature with total suspended solids, NO3− , PO3− 4 . and chemical oxygen demand; whereas dissolved oxygen, pH, conductivity, Ca, Mg, Na, K, alkalinity, Cl, SO 2− 4 , and Si were negatively correlated with hydrological factors. However, this study did not examine the link to microbiological parameters. Regarding pathogen contamination, the number of Escherichia coli was found higher in the wet season than the dry season.23 In contrast, a study conducted in the same area21 reported lower E coli concentrations in the October, the flood season, than that in April 2008, the dry season. The other study21 expressed that although the pathogens was significant associated with seasonality, there was no consistent evidence in this association. These inconclusive findings may be attributed to fact that the studies did not consider multivariate climate factors (eg, air temperature, rainfall, and humidity) in the analysis. These factors can cause changes in development of microbiological pathogens. Some change in water quality over time were quantified in some studies conducted in the Vietnam Mekong Delta,25,33 and the findings implied these changes were caused by the changes in climate conditions. The results showed that pH and nitrate remained within permissible levels, while all other parameters such as coliforms, suspended solids, phosphates, and ammonia exceeded the guideline levels set by national regulations. These studies suggest that these issues are related to climate change; however, no evidence in this relationship has been evaluated. In terms of knowledge gaps, the studies indicated that there was a big gap of knowledge on the impacts of climate change to water quality, especially to groundwater in the Mekong Delta region.4,32,33 For instance, the interaction between surface and ground water during a flooding
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event has not been investigated, resulting in a large gap of information required for developing adaptation strategies in the MDB. The study4 also indicated that it is necessary to more assess impacts of climate change on the groundwater resources in various parts of the MDB.
Results of Association Between Climate Conditions and Water-Related Diseases Waterborne Diseases. A few single-country studies were conducted in the Vietnam Mekong Delta. Increased diarrheal visits following flooding events were commonly reported in some studies,21,27,37,38 and diarrhea was considered to be of most concern for inhabitants living in Mekong Delta. Diarrhea was associated with disruption to normal water/sanitation services and the spreading of contamination due to flooding events, which can contaminate drinking water sources and inundate latrines, spreading pathogens in the environment. However, these studies had some limitations. First, data on diarrhea were obtained from interviews with inhabitants, so the results might be biased due to recall error of interviewees. Second, these studies did not examine the seasonal and spatial pattern of diarrhea corresponding to flood duration, intensified levels, and flood time. Such information could assist in better health preparedness of local health departments. Finally, these studies did not consider climate factors in analyzing the flooddiarrhea relationship. Very limited information about the groundwater resource size, use sustainability and quality is available from the literature. Only a few studies exist, focusing on some local areas within the Mekong Basin exist where they have made an assessment of resource, use and/or quality. Therefore, little can be said about potential climate change impacts. (Eastham et al, 2008)4(p59)
Some studies investigated the relationship between climate factors and cause-specific diarrhea in Vietnam Mekong Delta. The study conducted by Kien et al24 in 2005 indicated that increased rates of typhoid fever was associated with increase in annual floods, and the disease outbreaks were significantly correlated with temperature but not rainfall. Nevertheless, the timeseries were not properly designed to evaluate a short-term relationship between climate factors and the disease. The study by Kelly-Hope et al19 found that bacterial enteric diseases have distinct temporal and seasonal patterns, in which climate plays a role in defining high- and lowdisease period; however, climate factors did not appear to affect outbreaks. In another study, Kelly-Hope et al18 expressed that typhoid fever prevailed in the Mekong Delta and was mostly associated with vapor pressure and river/stream drinking water quality. The peak period of typhoid fever usually occurred prior to the rainy season, when river levels were low. Hence the epidemics are likely associated with scarcity of water and compromised hygiene practices.39-41 However, no study has investigated the influence of climate factors such as temperature, rainfall, and humidity on the patterns of this disease. Water-Related Mosquito-Borne Diseases. Malaria and dengue fever threaten to reemerge in the Vietnam Mekong Delta due to the changes in climate factors on the breeding of mosquito larvae.27 It was suggested that incidence of dengue fever be commonly increased in the flood season because people probably more relied on treating and storing river water in containers. The study24 indicated that the number of reported malaria cases peaked from October through January (during and after the rainy season), and most of the peaks of malaria occurred during disaster events in El Nino years. Nevertheless, this study did not examine the short-term patterns of malaria in relation to climate factors such as temperature, humidity, and rainfall. Other Water-Related Diseases. Leptospirosis and influenza were found to associate with climate factors in a few studies.22,24 Kien et al24 mentioned that in the Mekong Delta, increased influenza
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was associated with a lower mean temperature and higher humidity; meanwhile, the disease had the highest rates during the period of August to October. A multi-country study22 indicated that Vietnam, Cambodia, and Laos have been considered endemic for leptospirosis, and the outbreaks of this disease associated with rainfall. However, these studies did not quantify the relationship between the diseases and climate factors over time and locations. Studies on effects of climate factors on other water-related diseases such as fungal skin disease, eye infections, gynecological infections, which are caused by other types of water contaminants such as arsenic, pesticides, toxic algae, and industrial chemicals, have not been conducted anywhere else in the Mekong Delta.
Discussion The review indicated that a few studies provided preliminary evidences of association between hydroclimate factors and water quality; however, these evidences are not sufficient to evaluate the influence of variation in climate factors on water quality parameters as reported somewhere else. For instance, the study conducted by Harper et al12 in Canada found that weekly water volume input was positively associated with untreated water coliform levels and related to the gastrointestinal illness admitted into hospitals, and higher water temperatures will probably result in a higher pathogen survival in the environment.42 Besides the basic water quality parameters, studies in association between climate factors and chemicals contamination (eg, metals, pesticides) have been neglected in the MDB. The study indicated that climate change would influence on the fate and transport of chemical contaminants in agricultural systems.43 Increases in temperature and alteration in moisture characteristics may reduce the persistence of chemicals while changes in hydrologic characteristics can result in increasing the potential for contaminants to be transported to water supplies. For example, global warming is likely to reduce soil and aquatic concentrations of pesticides due to combination of elevated volatilization and degradation,44,45 whereas increases in the intensity and frequency of rain and storm events will increase the wet deposition of pesticides to aquatic systems.46,47 Climate change also changes the frequency and amount of pesticides used as agriculture shifts corresponding to the rapidly changing climate48; as a consequence, this will spread out the pesticide contamination due to runoff during the high rainy season. The potential adverse health effects caused by agricultural pesticide exposure can be a wide range of signs, symptoms, and diseases, including reduced eye-hand coordination, effects on cognitive abilities, developmental toxicity, estrogenic effects, antiandrogenic effects, congenital abnormalities, reduced stamina, pregnancy loss, and Parkinson’s disease.43 Most of studies indicated that increases in waterborne and vector-borne diseases associated with flooding events in the MDB; however, these study designs just focused on extreme events but not on annual variability of hydrometeorological conditions (eg, annual flood pulse). It is believed that regular short-term climate variability will still continue to cause problems for water and water-related health effects.30 Therefore, the effects of both unusual extreme events relating to long-term climate change and “normal” variability of climate need to be considered extensively in the MDB. Although the plausible mechanism underlying the present association between hydrometeorological factors and water-related diseases is unclear, there are several possible etiologic and meteorologic explanations. The reason for rainfall disease outbreaks is the change in the direction of flow of water systems and flow through channels that would not normally occur, resulting in substantial amounts of fecal polluted water into rivers, and this may be worsen in areas where sanitation services are insufficient and agricultural activities are located within catchments. Rainfall-related flood events were also found to be associated with other infectious diseases such as leptospirosis,49,50 hepatitis E, malaria,51,52 and acute respiratory disease.53
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The link between increased temperature and waterborne disease were possibly because of the blooms of various planktonic species. For example, cyanobacteria (blue-green algae) was found to be associated with dermatitis, respiratory problems and hepatitis,54 and dinoflagellates and diatoms can cause neurotoxicity and shellfish poisonings.55 One of the most clear effects of temperature on risk of waterborne disease relates to cholera,56 and this is attributed to the increased temperature-plankton bloom, resulting in increased cholera as it survives more with algae and plankton. Variability in temperature was also found to be associated with the risk of vector-borne disease because it can affect both the distribution of the vector and the effectiveness of pathogen transmission through the vector.57,58 The possible mechanisms for this relationship are increasing or decreasing survival of vector, changes in rate of vector population growth, feeding behavior, susceptibility of vector to pathogens, incubation period of the pathogen, seasonality of vector activity, and seasonality of pathogen transmission.59 Nevertheless, these relationships have been poorly investigated in the MDB. This current review has some limitations. The terms underinvestigated, underrecognized, and underreported might be seen in this review for several reasons. First, most of the health effects of climate changes are indirect, so it is difficult to identify climate change as the sole exposure factor responsible for a given health outcome. Second, in most developing areas, such as the MDB, research in climate change and health is in its infancy, so it is difficult to find high-quality and long-term research on this issue. Moreover, the articles included in this review are diverse, either project reports or research articles, so they have widely varying study designs, leading to variation in quality. However, because of the shortage of articles, all available articles that presented climate factors, water quality, and water-related diseases in the MDB were included for review. Information bias from included articles as extreme climate change is more likely reported, and the evidence borrowed from other locations in the world may be not applicable to the MDB.
Conclusion and Recommendations This systematic review provides a summary of the evidence on the association between climate factors, water quality, and water-related diseases in the MDB. Based on limitations and gaps of the existing studies, the review also provides some useful recommendations to support health sectors and international agencies in efforts to plan for further research, policy development, and adaptation strategies in the MDB. Although this review represents an initial attempt at summarizing the available evidence on the climate factors, water quality, and water-related diseases in the MDB, a number of recommendations for further research are provided below: •• In terms of water quality associated with climate factors, studies with more sensitive analysis are required to examine the short-term association between climate conditions and water quality parameters. Research on the relationship between climate conditions and salinity, chemical contamination, and pathogen contamination in both river water and groundwater supply should be further conducted to fill the gaps of knowledge and information. •• In terms of water related diseases in relation to climate factors, understanding of the pattern of diseases during and after a flooding event would be useful for public health preparedness and prevention. The variation of water-related diseases caused by an annual flood pulse, which is also of interest for regular preparedness and control in local health departments, should be investigated. The influence of other climate factors such as temperature, rainfall, and humidity need to be taken into account as potential exposure factors in climate-disease relationship in MDB. Other health issues such as dermatitis, respiratory illness and hepatitis and those potentially caused by cyanobacteria (blue-green algae) should also be considered in any comprehensive examination in climate-disease association.
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Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
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