The Impact of Climate Change on the Incidence of ...

77 The Impact of Climate Change on the Incidence of Infectious Waterborne Disease 77.1 Introduction.............................................................................................................................1017 Climate Change and Human Health

77.2 Waterborne Infectious Diseases............................................................................................1019 77.3 Meteorology and Waterborne Disease................................................................................1020 77.4 The Influence on Waterborne Disease.................................................................................1020 Rainfall • Extreme Weather Events • The Impact of Increased Temperature

Jean O’Dwyer University of Limerick

Aideen Dowling University of Limerick

Catherine Adley University of Limerick

77.5 Emerging Waterborne Bacterial Pathogens........................................................................1021 Mycobacterium avium Complex • Helicobacter pylori • Aeromonas hydrophyla

77.6 Climate Change and Infectious Disease in Europe........................................................... 1022 77.7 Summary and Conclusions...................................................................................................1024 Ongoing Epidemiological Research Highlighting the Links between Climatic Influences and Infectious Disease • Prioritization of Standardized Global Disease Surveillance • Further Development of Forecasting Models and Improvement of Public Health Infrastructure

References............................................................................................................................................1024

Preface Anthropogenic climate change is currently one of the biggest threats to humankind; with increases in average global temperature predicted to affect natural systems with detrimental consequences to human health. This chapter focuses on climate change and waterborne infectious disease. Meteorological phenomena can play a leading role in waterborne infectious disease epidemiology. The impact of meteorology on waterborne disease is moderated through the effects of rainfall frequency and intensity as well as temperature—both air and water temperatures—both of which are discussed within this section. Also investigated are emerging waterborne infectious diseases, which may prove to be problematic in coming years and present problems to countries unequipped to monitor, report, and moderate diverse waterborne pathogens. This chapter provides a focus on Europe and offers recommendations for adaptability, prevention, and preparation, which can be implemented at a global level.

77.1 Introduction 77.1.1 Climate Change and Human Health Over the past century, acceleration in economic activity coupled with a staggering increase in fossil fuel consumption has led to an environmental impact of unprecedented proportions; this is termed climate change. There is near unanimous scientific consensus, for example, 97% of publishing scientists agree

[9] that rising atmospheric concentrations of greenhouse gases (GHGs) attributed to anthropogenic emissions causing warming (and other climatic changes) at Earth’s surface. Climatological research over the past two decades makes clear that Earth’s climate will change in response to atmospheric GHG accumulation. The unusually rapid temperature rise (0·5°C) since the mid-1970s is substantially attributable to this anthropogenic increase in GHGs [30]. The Intergovernmental Panel on 1017

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Urban Water Reuse Handbook

Climate Change (IPCC), representing the published results of leading climatological modeling groups around the world, forecasts that global mean temperatures will continue to rise over the twenty-first century if GHG emissions continue unabated. The panel makes their predictions based on representative concentration pathways (RCPs). RCPs are four GHG concentration trajectories adopted by the IPCC for its fifth assessment report (AR5). They describe four possible climate futures, all of which are considered possible depending on how much GHGs are emitted in the years to come. The four RCPs (RCP2.6, RCP4.5, RCP6, and RCP8.5) are named after a possible range of radiative forcing values in the year 2100 (+2.6, +4.5, +6.0, and +8.5 W/m2, respectively) [45]. Radiative forcing describes the difference of radiant energy received by the Earth and energy radiated back to space. Under the assumptions of the concentration-driven RCPs and with respect to preindustrial conditions, global temperatures averaged in the period 2081–2100 are projected to likely exceed 1.5°C above preindustrial values for RCP4.5, RCP6.0, and RCP8.5 (high confidence) and are likely to exceed 2°C above preindustrial for RCP6.0 and RCP8.5 (high confidence) [43] as shown in Figure 77.1 [1]. Global warming is not happening uniformly. It is occurring faster during the winter months and the rate of warming is more staggering at higher latitudes. In addition, heat is building up at an unprecedented rate in the ocean; down to 3 km [28] and, as a result, water vapor in the atmosphere is increasing [12]. Sea ice and ice shelves are melting, with September 2012 seeing the lowest sea ice extent ever recorded by satellites at

1.32 million square miles (3.41 million square kilometers) [5]. The result of this heating is a measurable, significant change to the hydrological cycle. There is evidence that the climatic system is experiencing instabilities as extreme weather events, such as prolonged droughts and excessive rainfall (>5 cm/day), which have increased in both intensity and frequency. Some of the projected changes, both globally and specifically in Europe, are detailed in Table 77.1. The climatic system displays complex interactions of interconnected components, including the atmosphere, hydrosphere, cryosphere, biosphere, and geosphere. Changes in global temperature will have adverse effects on most systems and will undoubtedly have implications in human health. Figure 77.2 summarizes some key pathways in which anthropogenic GHG emission will affect the environment and subsequently human health. Of particular concern is the effect of a changing climate on the incidence of waterborne infectious disease. Global climate change will interfere with interactions within the hydrologic cycle not only by altering mean meteorological measures, but also by increasing the frequency of extreme events such as excessive precipitation, storm surges, floods, and droughts, many of which have already been seen over the past decade. Structural damage as well as the direct loss of human life because of these extreme weather events is highly publicized in the media. However, a potentially more catastrophic eventuality looms in the form of the increase in transmission, frequency, and dispersal of waterborne infectious diseases.

RCP8.5 Business-as-usual 2.1 trillion tons carbon

8°C Increase in average global temperature

Downloaded by [Jean O'Dwyer] at 07:19 06 January 2016

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7°C 6°C RCP6.0 emissions peak 2080 1.4 trillion tons carbon

5°C 4°C

RCP4.5 emissions peak 2040–50 1.2 trillion tons carbon

3°C 2°C 1°C 2013

0 1950

2000

2050

2100

2150

2200

Global temperature projections for various RCP scenarios

FIGURE 77.1 Global temperature projections for the future based on the representative concentration pathways developed for the intergovernmental panel on climate change report 2005. (Adapted from Architecture 2030, 2012. http://architecture2030.org/files/roadmap_web.pdf. Permission granted December 2, 2013.)


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The Impact of Climate Change on the Incidence of Infectious Waterborne Disease TABLE 77.1 Observed and Global Projections for Climate Change, Globally and in Europe Observed and Projected Climate Change Impacts on the Environment and Human Health Key Climate Variables Global temperature

European temperature


Precipitation

Present Situation

Future Projections

IPCC reports that global average temperature—both land and ocean—has shown an increase of between 0.77°C and 0.80°C in mean temperature as compared to the pre-industrial average. The average temperature for the European Land Area for the decade of 2002–2011 is 1.3°C above preindustrial levels. It was the warmest decade ever recorded with heat waves increasing both in frequency and in length. Precipitation changes are more spatial and temporal than temperature. Since the 1950s, precipitation has been increasing in Europe throughout the winter but decreasing in parts of southern Europe. In western Europe, intense precipitation events have contributed significantly to the increase.

Further rise in temperature is expected to be between 1.1°C and 6.4°C by 2100.

Anthropogenic Greenhouse Gas Emissions

Environmental Effects

Extreme Weather Events: -Frequency -Severity -Geography

Climate Change

Changes in mean climatic conditions and variability: -Temperature -Precipitation -Humidity -Wind patterns

Sea-level rise: -Salination of coastal land and freshwater -Storm surges

Effects on Ecosystems: -Land -Sea -Particular Species

Further rise in temperature is expected to be between 2.5°C and 4.0°C by 2100. The largest increases are expected in Northern and Eastern Europe. Most climatic models project a continued increase in precipitation for Northern Europe and decrease in Southern Europe. The number of days with intense precipitation is projected to increase.

Health Effects

Increase in flooding and extreme precipitation as well as drought

Microbiological proliferation: creation of unsafe drinking water

Changes in infectious disease geography and seasonality

Natural Climate Change: Terrestrial, Solar, Planetary, & Orbital

FIGURE 77.2 The effect of anthropogenic emissions of environment and health.

77.2 Waterborne Infectious Diseases A variety of microorganisms (viruses, bacteria, and protozoans) have the capacity to transmit disease through contact with contaminated water as shown in Table 77.2. The health implications of exposure to pathogenic bacteria, viruses, and protozoa in drinking water are diverse. Worldwide, the most commonly reported manifestation of waterborne disease is in the form of gastrointestinal illness—nausea, vomiting, and diarrhea.


However, in individuals who are more vulnerable to illness, that is, the young, the elderly, and the immunocompromised, the effects can be far more severe. As a result, globally, over 1.5 million people die each year from unsafe water, inadequate sanitation, and insufﬁcient hygiene as a result of diarrheal diseases, schistosomiasis, and others [34]. Transmission of infectious disease is determined by many factors, including extrinsic social, economic, climatic, and ecological conditions [46] and intrinsic human immunity [25]. In

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Urban Water Reuse Handbook TABLE 77.2 Major Waterborne Disease, Transmission Pathways, and Clinical Features Organism

Disease

Transmission

Clinical Features

Protozoa Giardia duodenalis

Giardiasis

Cryptosporidium parvum

Cryptosporidiosis

Vibrio cholerae Salmonella typhi

Cholera Typhoid

Drinking water Drinking Water

Shigella spp. Campylobacter spp. Enterotoxigenic and Enterohemorrhagic E. coli Legionella

Shigellosis Camplyobacterosis

Drinking and recreational water Drinking and recreational water Drinking water

Legionnaires disease

Drinking and recreational water

Fecal oral spread through drinking or recreational water Fecal oral spread through drinking or recreational water

Diarrhea and abdominal pain, weight loss, and failure to thrive Diarrhea often prolonged


Bacteria

relation to urban drinking water, the transmission of waterborne infectious disease can manifest only if the supply has become sufficiently contaminated, or has failed to be treated correctly or the treatment has failed entirely; with an ever-increasing demand on water supplies, these situations are becoming more prevalent. Drinking water may also become contaminated as a result of increases in incidences of heavy rainfall, snow melts, and flooding. These events cause a surge in water flow, causing sewers or wastewater treatment outputs to overflow directly into a surface water body—often this microbiological burden can be too great for water treatment facilities to overcome.

77.3 Meteorology and Waterborne Disease In terms of climate change, it is important to establish the current impact of water-related illnesses and try to incorporate future predictions to aid policy formulation and improve the adaptive capacity of those nations at greatest risk. To understand the influence of the global meteorological system on water-related disease, we must first distinguish between weather and climate. Weather refers to the short term, usually day to day, meteorological events that take place in local areas. Weather is erratic and variable; changing daily. In contrast, climate usually refers to the “average” conditions for a given location based on its meteorological record (day to day weather over time). While the effects of weather are quite obvious—extreme rainfall events may lead to flooding—changes in climate are more subtle, taking decades to understand and form enough trends to interpret accurately. Accordingly, in relation to our changing climate we must discuss the effects of short-term weather in the form of rainfall and extreme weather events and the more subtle climatic change in temperature. However, while we will treat both meteorological classifications as separate entities, it must not be forgotten that they are interconnected; weather depicting climate and climate influencing weather.


Watery diarrhea, may be severe Fever, malaise, and abdominal pain with high mortality Diarrhea frequently with blood loss Diarrhea frequently with blood loss Watery or bloody diarrhea can lead to hemolytic uremic syndrome in children Watery diarrhea may be severe

77.4 The Influence on Waterborne Disease Outbreaks of waterborne disease as a result of the contamination of community water systems have the potential to cause extensive illness among the population; particularly in areas where infrastructure is not up to par. The impact of meteorology on waterborne disease is moderated through the effects of rainfall frequency and intensity as well as temperature; both air and water temperatures. The effects are varied and are pathogen specific, meaning that the risk to human health is entirely a function of local conditions including infrastructure and water treatment capacities. The link between these three parameters must not be understated and is likely to become more evident as climate change scenarios come to fruition. When analyzing the consequences of a changing climate, we must look at both “normal” or “static” weather variables—precipitation, mean air, and water temperature—but, we must also allow some focus on “extreme weather events,” which are likely to increase in both frequency and intensity over the coming years. In this chapter, we will discuss the evidence of the impact of climate change on the epidemiology of waterborne disease in relation to three variables:

1. Rainfall 2. Temperature 3. Extreme weather events

77.4.1 Rainfall One of the most common manifestations of waterborne disease in gastrointestinal illness and many of these enteric diseases that cause this health problem show a seasonal pattern, suggesting that they are sensitive to variations in climatic factors. Levels of precipitation play a pertinent role in influencing the contamination of water and hence increase the vulnerability


The Impact of Climate Change on the Incidence of Infectious Waterborne Disease

of drinking water supplies. It is thought that the frequency of heavy precipitation events has increased over many midlatitude regions since the 1950s, even where there has been a reduction in average precipitation [6]. Of pressing concern is the pollution of water bodies with fecal contamination, particularly from nonpoint sources such as agriculture. Fecal pathogen events in rivers, lakes, and reservoirs have been shown to be associated with rainfall events. Heavy “flash” rainfall or periods of prolonged rainfall can mobilize pathogens within the environment, increasing runoff from agriculture and transporting this microbiologically rich medium into rivers, coastal waters, and groundwater wells [40]. Similarly, during periods of heavy rainfall, a cross-contamination can occur between municipal water and drinking water as water treatment plants may become overwhelmed. This may cause sewage overflow into drinking water supply chains, or may flow directly into local waterways [41]. Lastly, increased levels of rainfall can also lead to flooding. While the structural damages associated with flooding are well reported, the increased exposure to waterborne pathogens is lesser known. This bodes a serious health problem, in both developed and undeveloped countries and can create pandemic outbreaks of infectious disease [15]. Significant research is now available highlighting the links between climate and health. A study based on England and Wales found that 20% of waterborne outbreaks from surface water in the past century were associated with a sustained period of low rainfall, while 10% were associated with heavy rainfall [32]. Similarly, outbreaks of Cryptosporidium, Giardia, E. coli, and other infections have been associated with heavy rainfall events in countries where a public water supply is well regulated [2,10]. Looking to the United States, some of the largest outbreaks of waterborne disease in North America have resulted after notable rainfall events. For example, in May 2000, heavy rainfall in Walkerton, Ontario resulted in approximately 2300 illnesses and 7 deaths after the town’s drinking water became contaminated with E. coli O157: H7 and Campylobacter jejuni [21]. In the United States, from 1948 to 1994, heavy rainfall correlated with more than half of the outbreaks of waterborne diseases [10]. In terms of groundwater aquifers, a recent study in the Republic of Ireland has shown that the strongest predictor of reporting contamination with E. coli was rainfall, indicating that contamination was 1.2 times more likely with every 1 mm increase in rainfall [33].

77.4.2 Extreme Weather Events The impact of extreme weather events (EWEs) on waterborne illness may be widespread and is often a factor in triggering waterborne disease outbreaks [10]. Curriero et al. found that more than half of the reported waterborne disease outbreaks in the United States since the 1950s have followed a period of extreme rainfall. Of these outbreaks, 68% followed severe storms. There is also evidence to support that water-related events like El Nino Southern Oscillation, hurricanes, and typhoons are becoming more frequent, intense, and of greater


1021

duration [29]. Flooding caused by heavy rains or disaster events such as hurricanes or tsunamis can create vast areas of standing water and with it new areas for potential pathogen exposures. It is expected that effects linked to climate change such as elevations in extreme hydrological events may further contribute to water quality impairment by fecal pollution of livestock origin and thus further increase the potential for human exposures and illness. In relation to surface water bodies, an investigation of the effects of wet weather on pathogen and indicator concentrations in an agriculture-intensive watershed in Ontario observed that during storm events, the peak Campylobacter concentration arrived earlier than the peak turbidity level. The authors speculated that this was because pathogens are generally in limited supply within a watershed and are therefore more likely to be ﬂushed out of the stream before the turbidity level declines [11]. As mentioned previously, El Niño seasons have been associated with outbreaks of infectious disease; both vector and waterborne, in many areas [18]. El Niño events are predicted to become more common and more severe with an increase in global temperature. As a result of the effects of an El Niño event in 1997, the incidence of infection of patients with diarrheal disease in Lima, Peru, increased significantly due to an increase in temperature [38]. An analysis of the daily hospital data ensued subsequent to the event and was found that the hospital admittance for gastrointestinal symptoms went up by 8% per 1°C increase in temperature [8].

77.4.3 The Impact of Increased Temperature Transmission of enteric disease can possibly be increased by high temperatures by the direct effect on the growth rate of an organism in the environment [3,4]. The areas affected by drought have increased since the 1970s [23] and this may lead to an increase in exposure to pathogenic microorganisms as a result of pollution concentration in depleted water supplies. In terms of temperature, in general, both salmonella and cholera bacteria, for example, proliferate more rapidly at higher temperatures, salmonella in animal gut and food, and cholera in water [19]. In a technical report produced for the European Centre for Disease Control (ECDC), campylobacteriosis and salmonellosis were cited with the highest frequency in association with air temperature, and campylobacteriosis and non-cholera vibrio infections were reported in association with water temperature.

77.5 Emerging Waterborne Bacterial Pathogens While climate change is likely to increase the incidence of waterborne infectious disease outbreaks, this is not the only area of concern. Emerging waterborne bacterial pathogens are also an area of immense interest and may burden many countries that have not even been monitoring for these pathogenic organisms to date. Detailed here are emerging pathogens that can be spread

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through the consumption of drinking water. Worryingly, these organisms do not correlate with the presence of indicator organisms like E. coli or coliform bacteria and in most cases there is no satisfactory microbiological indication of their presence in the environment. Further research is needed in order to ascertain the real significance and epidemiology of the diseases caused by these organisms.


77.5.1 Mycobacterium avium Complex The Mycobacterium avium complex (MAC) consists of 28 genotypes of two distinct bacterial species: Mycobacteriumavium and Mycobacterium intracellulare. Like many bacterial pathogens, they are opportunistic and represent the greatest danger to those individuals who are immuocompromised, particularly individuals infected with human immunodeficiency virus (HIV). The organisms have been identified in a diverse range of environmental sources including lakes, streams, rivers springs, soil, piped water supplies, and plants. Importantly, in this context, MAC organisms have been isolated from natural and drinking water distribution systems in the United States [44]. MAC organisms are hardy, surviving under various, normally stressful, conditions. They have been found in water at temperatures of up to 51°C and can grow over a wide pH range. MACs are highly resistant to chlorine and other chemical disinfectants, resulting in standard methods of water treatment not eliminating these organisms from the drinking water distribution system. As MAC organisms grow in biofilms, they represent a real challenge for water quality should they become a common visitor to drinking water systems. The clinical presentation of MAC infections can include a productive cough, fatigue, fever, weight loss, and night sweats.

77.5.2 Helicobacter pylori Helicobacter pylori is commonly associated with gastritis and has been implicated in duodenal and peptic ulcers and stomach cancer. However, most people who become infected by the organism remain asymptomatic [22]. There are no reports that demonstrate H. pylori been isolated from an environmental supply, utilizing traditional culture-based method [16]. Instead, molecular methods including fluorescence in situ hybridization and polymerase chain reaction (PCR), have been successful in detecting the pathogen. How H. pylori is transmitted through human exposure is still not fully understood [27]. The organism has been recovered from saliva, dental plaque, stomach, and fecal samples which could be conclusive of oral–oral or fecal– oral transmission. If this is the case, water may play a significant role in transmission, particularly in situations with improper sanitation and hygiene.

77.5.3 Aeromonas hydrophyla Over the last few years, A. hydrophila has been attributed due recognition within the public health sector. It has now been recognized as an opportunistic pathogen, being branded a potential



agent of gastroenteritis, septicemia, meningitis, and wound infections [20]. The organism itself is a Gram negative, rod shaped, non-spore forming facultative anaerobic bacilli, native to the family Aeromonadaceae. A. hydrophila are abundant in the natural environment and have been isolated from food, drinking water, and aquatic environments [26]. In uncontaminated rivers and lakes, concentrations of Aeromonas spp. are usually around 102 colony-forming units (CFU)/mL. Groundwater generally contains less than 1 CFU/mL. Drinking water directly leaving the treatment plant has been found to contain between 0 and 102 CFU/mL [7]. Drinking water in distribution systems can display higher Aeromonas concentrations, due to the growth in biofilms. Aeromonas spp. have been found to grow between 5°C and 45°C. A. hydrophila is resistant to standard chlorine treatments, possibly persisting inside biofilms [14]. The common routes of infection suggested for Aeromonas are the ingestion of contaminated water or food or contact of the organism with a break in the skin. Drinking or natural mineral water can be a possible source of contamination for humans.

77.6 Climate Change and Infectious Disease in Europe Major causes of diarrheal illness linked to the contamination of drinking water with microorganisms are Cryptosporidium, E. coli, Giardia, Shigella, and Campylobacter. Cholera is also another pathogenic organism highly associated with drinking water; however, its prevalence in the environment has decreased throughout the late twentieth and early twenty-first century with only 11 confirmed cases in 2006. However, internationally, cholera outbreaks during the warmer months display a seasonal pattern in higher absolute latitudes and climate change might influence the strength, duration, or appearance of such a seasonal pattern [13]. The IPCC predicts that Europe will experience a variance of impacts from global climate change. The variance of impacts is a result of the diverse geographic, demographic, ecological, and socioeconomic conditions in the region. Although the impacts are not uniform across the continent, the annual average temperature and mean precipitation are predicted to experience significant changes overall, with warmer winters predicted for Northern Europe and warmer summers predicted for the South of the continent [17]. Conservative projections foresee global mean air temperatures increasing by 1.8–4.0°C this century, while other models suggest a range of increase of 1.1–6.4°C. The global average temperature is now 0.8°C higher than between 1850 and 1919, while in Europe this average is 1.4°C higher [35]. As to the rate of change, the last decade was the warmest on record, with 2005 being the hottest. The most dramatic increase has been recorded in the Arctic region of Europe, where the temperatures have risen by 3°C over the last 90 years [35]. Northern Europe is also the geographical area with the biggest projected temperature increase according to climate change scenarios [35]. These changes in both temperature and precipitation are likely to influence both water- and foodborne pathogens by altering the effects

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The Impact of Climate Change on the Incidence of Infectious Waterborne Disease TABLE 77.3 Cases of Five Waterborne Diseases Reported in Europe between 1995 and 2010


Campylobacter

Cryptosporidium

Year

Number of Cases

Increase/ Decrease

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

85130.00 91285.00 105797.00 149561.00 152617.00 170065.00 193708.00 186780.00 170218.00 182598.00 197802.00 175908.00 200807.00 190579.00 198862.00 215058.00

0 7.23 15.90 41.37 2.04 11.43 13.90 −3.58 −8.87 7.27 8.33 −11.07 14.15 −5.09 4.35 8.14

Number of Cases 6814.00 4070.00 5724.00 5163.00 6456.00 7833.00 6389.00 4940.00 8413.00 6164.00 7960.00 6801.00 6255.00 7028.00 8016.00 6605.00

VTEC

Giardia

Increase/ Decrease

Number of Cases

Increase/ Decrease

0 −40.27 40.64 −9.80 25.04 21.33 −18.43 −22.68 70.30 −26.73 29.14 −14.56 −8.03 12.36 14.06 −17.60

3209.00 3046.00 3714.00 3597.00 6893.00 6847.00 8675.00 9196.00 9170.00 9773.00 5199.00 3262.00 2908.00 3164.00 3583.00 3656.00

0 −5.08 21.93 −3.15 91.63 −0.67 26.70 6.01 −0.28 6.58 −46.80 −37.26 −10.85 8.80 13.24 2.04

Number of Cases 12788.00 11891.00 12794.00 11614.00 11380.00 10196.00 13833.00 12267.00 12232.00 17101.00 27240.00 16542.00 14513.00 18274.00 16564.00 16844.00

Legionella

Increase/ Decrease

Number of Cases

Increase/ Decrease

0 −7.01 7.59 −9.22 −2.01 −10.40 35.67 −11.32 −0.29 39.81 59.29 −39.27 −12.27 25.91 −9.36 1.69

588.00 817.00 1233.00 1462.00 2263.00 2421.00 3763.00 4791.00 4503.00 4635.00 4094.00 5512.00 5169.00 5279.00 5109.00 5801.00

0 38.95 50.92 18.57 54.79 6.98 55.43 27.32 −6.01 2.93 −11.67 34.64 −6.22 2.13 −3.22 13.54

of mixed etiology, but the actual disease burden in Europe is difficult to approximate and most likely underestimated. Table 77.3 demonstrates the fluctuations in the cases of five water-related infectious diseases for the years of 1995–2010. Figure 77.3 visually displays the data from Table 77.3, and it can be suggested that there has been an upward trend in reported cases. However, the increases could be attributed to an increase in monitoring regimes, which have become more stringent in recent years. However, it is thought that many cases are still unreported. In 2006, merely 17 waterborne outbreaks were

of environmental exposure pathways. It is well established that waterborne diseases display a strong correlation with seasonal variation [39], be it through climatic or anthropogenic variation. Although infectious disease outbreaks have been linked to individual weather events, there have been few attempts to detect and attribute temporal trends in infectious diseases to climate change [42]. Many studies have projected future levels of disease spread in response to climate change, but there are currently no means for verifying the accuracy of these models. Unfortunately, waterborne outbreaks have the potential to be rather large and 30000

250000

25000

200000 Crypto

20000 150000 15000

VTEC Giardia Legionella

100000

Campylobacter

10000 50000

5000

0

0

9

20 1

8

20 0

7

20 0

6

20 0

5

20 0

4

20 0

3

20 0

2

20 0

1

20 0

0

20 0

9

20 0

8

19 9

7

19 9

6

19 9

19 9

19 9

5

0

FIGURE 77.3 Graph showing the number of cases of five waterborne diseases as reported to the ECDC from 1995 to 2010.



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reported by five countries in Europe, clearly significantly underreported. They involved a total of 3952 patients, of which 181 were hospitalized, afflicted by a number of causative agents including campylobacter, calicivirus, giardia, and cryptosporidium [40]. Erratic and extreme precipitation events can overwhelm water treatment plants [24] and lead to cryptosporidium outbreaks due to oocysts infiltrating drinking-water reservoirs from springs and lakes and persisting in the water distribution system. In Europe, flooding has rarely been associated with an increased risk of waterborne disease outbreaks, but a few exceptions exist in the UK [37], Finland [31], and Sweden [36]. Projected increases in the intensity and frequency of rainfall in the northern regions could lead to cryptosporidium infiltration in water-treatment and distribution systems [41]. Northern European countries report a more prominent potential increase in climate change risk, as opposed to those from southern European countries, where projected decreases in precipitation could reduce these risks. However, these observations also reflect reporting bias; those countries with better EU cryptosporidium notifications reported a climate change risk, whereas those countries with incomplete (or no) cryptosporidium notifications considered the risk to be low.

77.7 Summary and Conclusions The purpose of this chapter is to highlight the evidence pertaining to the links between climatic factors and waterborne infectious disease. The effects of temperature, precipitation, and extreme weather events on the incidence of infectious disease has been noted within academic literature and has demonstrably shown to be a key indicator on climate change risks in relation to public health. While intrinsic waterborne infectious disease appears to have been increasing in both Europe and the United States, this is not the only troubling factor. Emerging and re-emerging waterborne infectious diseases are also an area of attention and may prove to be a problematic area of global public health in the years to come. Many studies have described seasonal fluctuations in infectious disease, but few have documented long-term trends associated with a climate-disease interface. A variety of models have been and will continue to be developed with the function of being able to systematically and statistically simulate climatic changes and accordingly predict potential disease outbreaks although very few have successfully controlled for socio-demographic or external environmental indicators. The current gaps in knowledge invite scope for further research in the following areas.

77.7.1 Ongoing Epidemiological Research Highlighting the Links between Climatic Influences and Infectious Disease A barrier to research in relation to infectious disease as a function of climatology has been the need to develop a relationship between climate and disease patterns across diverse populations and geographical regions. For this barrier to be overcome,



collaborations between research of different nationalities need to be facilitated. Similarly, collaborations between different research fields are paramount to progress. As the subject area requires specialization within many scientific fields, there is a need for climatologists, ecologists, and epidemiologists to combine their knowledge in order to expand the breadth of information being reported and published.

77.7.2 Prioritization of Standardized Global Disease Surveillance Perhaps the biggest obstacle to coherent reporting of infectious disease outbreaks is the heterogeneity of data collection. It is difficult to ascertain correlation and causation on a global scale as there is an inconsistency in the way data is monitored, collected, and reported. Furthermore, it is near impossible to compare country-specific incidences of infectious disease as the number of incidences may be grossly underestimated if the monitoring and reporting is insufficient. Homogeneity is required across nations in order to establish accurate, representative data that can be used for modeling and epidemiological analysis.

77.7.3 Further Development of Forecasting Models and Improvement of Public Health Infrastructure Models are an important tool for forecasting the health implications associated with changing climatic conditions. In order for models to be both useful and significant, there must be an integration of multidisciplinary influences including social and environmental considerations. Also needed is training within the public sphere, particularly in relation to emergency response and prevention and control programs. Improved public understanding is paramount to the adaptive capacity of the public to ensure an intelligent response to projected health outcomes of climate change.

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The Impact of Climate Change on the Incidence of Infectious Waterborne Disease

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