Microbial Exposure Assessment of Waterborne Pathogens

The large number of waterborne illnesses in Ireland and worldwide has highlighted the need to enhance strategies that minimize human exposure to pathogens in drinking water supplies. Waterborne pathogens of public concern together with relevant national and international legislation are reviewed in this study. Cryptosporidium species and pathogenic Escherichia coli are among pathogens of primary concern. The organisms originate from the gastrointestinal tract of animals and humans. They may be associated with persistent contamination of water sources, survive for long periods in the environment, and, in particular in the case of Cryptosporidium species, may survive in chlorinated water supplies. Prevention of waterborne infection should emphasize source protection in addition to water treatment. Risk assessment models can play an important role in protecting natural water systems from contamination with these pathogens. Qualitative approaches can provide an effective means of assessing risks with minimum resources and limited data; however, they lack the precision and predictive ability of fully quantitative approaches. Thirteen quantitative simulation models that could potentially be used for modeling bacterial pollutants in agricultural watersheds have been assessed in this study. No one model suits all modeling criteria. Pathogen predictions have proved variable and no model was capable of accounting for all geological and hydrological factors in addition to modeling the physical transport of bacteria in surface runoff. This assessment summarizes commonly used models and their capacity to model water pollution while also providing a good reference point for the microbial risk assessment of waterborne pathogens.     

Microbial ecology of drinking water distribution systems

The supply of clean drinking water is a major, and relatively recent, public health milestone. Control of microbial growth in drinking water distribution systems, often achieved through the addition of disinfectants, is essential to limiting waterborne illness, particularly in immunocompromised subpopulations. Recent inquiries into the microbial ecology of distribution systems have found that pathogen resistance to chlorination is affected by microbial community diversity and interspecies relationships. Research indicates that multispecies biofilms are generally more resistant to disinfection than single-species biofilms. Other recent findings are the increased survival of the bacterial pathogen Legionella pneumophila when present inside its protozoan host Hartmannella vermiformis and the depletion of chloramine disinfectant residuals by nitrifying bacteria, leading to increased overall microbial growth. Interactions such as these are unaccounted for in current disinfection models. An understanding of the microbial ecology of distribution systems is necessary to design innovative and effective control strategies that will ensure safe and high-quality drinking water.     

Predicting chlorine decay and THM formation in water supply systems

In 1976, the US Environmental Protection Agency (USEPA) published the results of a national survey that showed that chloroform and other trihalomethanes (THMs) were ubiquitous in chlorinated drinking water. Also in 1976, the US National Cancer Institute published results linking chloroform to cancer in laboratory animals, thus giving rise to an important public health issue. Although numerous disinfection by-products (DBPs) have been reported in the literature since that time, with more than 700 confirmed species to date, only a small number have been addressed in either quantitative or health effects studies. The DBPs that have been quantified in drinking water are generally present at low to mid μg/l levels or below. Approximately 50% of the total organic halide (TOX) formed during the chlorination of drinking water and more than 50% of the assimilable organic carbon (AOC) formed during ozonation of drinking water is still not accounted for and little is known about the potential toxicity of many of the vast number of DBPs present in drinking water. The presence of free chlorine is a prerequisite to THM formation. Therefore, a robust understanding of the mechanisms of both chlorine decay and THM formation are fundamental to the management of THMs in water supply systems. This paper presents a review of work undertaken to improve our understanding of these key phenomena and highlights areas of vulnerability in our knowledge and so recommends areas of future research.     

Survival and multiplication of Legionella pneumophila in municipal drinking water systems.

Studies were conducted to investigate the survival and multiplication of Legionella spp. in public drinking water supplies. An attempt was made, over a period of several years, to isolate legionellae from a municipal system. Sampling sites included the river water supply, treatment plant, finished water reservoir system, mains, and distribution taps. Despite the use of several isolation techniques, Legionella spp. could not be detected in any of the samples other than those collected from the river. It was hypothesized that this was due to the maintenance of a chlorine residual throughout the system. To investigate the potential for Legionella growth, additional water samples, collected from throughout the system, were dechlorinated, pasteurized, and inoculated with Legionella pneumophila. Subsequent growth indicated that many of these samples, especially those collected from areas affected by an accumulation of algal materials, exhibited a much greater ability to support Legionella multiplication than did river water prior to treatment. Chemical analyses were also performed on these samples. Correlation of chemical data and experimental growth results indicated that the chemical environment significantly affects the ability of the water to support multiplication, with turbidity, organic carbon, and certain metals being of particular importance. These studies indicate that the potential exists for Legionella growth within municipal systems and support the hypothesis that public water supplies may contaminate the plumbing systems of hospitals and other large buildings. The results also suggest that useful methods to control this contamination include adequate treatment plant filtration, maintenance of a chlorine residual throughout the treatment and distribution network, and effective covering of open reservoirs.     

Escherichia coli: the best biological drinking water indicator for public health protection

Public health protection requires an indicator of fecal pollution. It is not necessary to analyse drinking water for all pathogens. Escherichia coli is found in all mammal faeces at concentrations of 10 log 9(-1), but it does not multiply appreciably in the environment. In the 1890s, it was chosen as the biological indicator of water treatment safety. Because of method deficiencies, E. coli surrogates such as the 'fecal coliform' and total coliforms tests were developed and became part of drinking water regulations. With the advent of the Defined Substrate Technology in the late 1980s, it became possible to analyse drinking water directly for E. coli (and, simultaneously, total coliforms) inexpensively and simply. Accordingly, E. coli was re-inserted in the drinking water regulations. E. coli survives in drinking water for between 4 and 12 weeks, depending on environmental conditions (temperature, microflora, etc.). Bacteria and viruses are approximately equally oxidant-sensitive, but parasites are less so. Under the conditions in distribution systems, E. coli will be much more long-lived. Therefore, under most circumstances it is possible to design a monitoring program that permits public health protection at a modest cost. Drinking water regulations currently require infrequent monitoring which may not adequately detect intermittent contamination events; however, it is cost-effective to markedly increase testing with E. coli to better protect the public's health. Comparison with other practical candidate fecal indicators shows that E. coli is far superior overall.     

Incidence of Staphylococcus aureus, coliforms and antibiotic-resistant strains of Escherichia coli in rural water supplies in Port Harcourt

The bacteriological quality of some rural water supplies in Port Harcourt was monitored over a 3 month period. The supplies were unsatisfactory as judged by standard plate counts (10(3)/ml) and the presence of presumptive and faecal coliforms and Staphylococcus aureus. The recovery of potentially pathogenic bacteria (e.g. Pseudomonas aeruginosa) further substantiated the existence of health hazards. The most frequently isolated coliforms were Escherichia coli, Enterobacter aerogenes and Klebsiella pneumoniae. Coliform contamination was greater in well water than in river or stream water samples. An antibiotic sensitivity test revealed that 17.5-27.2% of E. coli strains were resistant to three or more antibiotics. Escherichia coli isolated from well water samples exhibited the greatest degree of multiple resistance. Some strains were resistant to all the six antibiotics tested. The danger of an epidemic of waterborne diseases in the communities as a result of drinking water from these non-potable sources is noted.     

Incidence of Staphylococcus aureus, coliforms and antibiotic-resistant strains of Escherichia coli in rural water supplies in Port Harcourt

The bacteriological quality of some rural water supplies in Port Harcourt was monitored over a 3 month period. The supplies were unsatisfactory as judged by standard plate counts (10³/ml) and the presence of presumptive and faecal coliforms and Staphylococcus aureus. The recovery of potentially pathogenic bacteria (e.g. Pseudomonas aeruginosa ) further substantiated the existence of health hazards. The most frequently isolated coliforms were Escherichia coli, Enterobacter aerogenes and Klebsiella pneumoniae. Coliform contamination was greater in well water than in river or stream water samples. An antibiotic sensitivity test revealed that 17.5–27.2% of E. coli strains were resistant to three or more antibiotics. Escherichia coli isolated from well water samples exhibited the greatest degree of multiple resistance. Some strains were resistant to all the six antibiotics tested. The danger of an epidemic of waterborne diseases in the communities as a result of drinking water from these non-potable sources is noted.     

Failure of the most-probable-number technique to detect coliforms in drinking water and raw water supplies.

A procedure was developed to detect false-negative reactions (interference) in the standard most-probable-number (S-MPN) technique for coliform enumeration of untreated surface water and potable water supplies. This modified MPN (M-MPN) procedure allowed a quantitative assessment of the interference with coliform detection in untreated surface water and potable water supplies. Coliform interference was found to occur in the presumptive, confirmed, and completed tests of the S-MPN technique. When coliforms were present, interference with their detection occurred in over 80% of the samples. The inferior nature of the S-MPN was revealed by the 100% increase in the incidence of completed coliform-positive drinking water samples obtained with the M-MPN technique. The M-MPN procedure was also superior to the standard membrane filter technique. Eight different species of coliforms were recovered from false-negative tests, including Citrobacter, Enterobacter, Klebsiella, and Escherichia coli (in decreasing order of occurrence). The use of standard MPN techniques for monitoring potable water supplies may lead to a false security that the drinking water supply is potable, i.e., free from indicator bacteria.     

Molecular assessment of bacterial pathogens - a contribution to drinking water safety

Human bacterial pathogens are considered as an increasing threat to drinking water supplies worldwide because of the growing demand of high-quality drinking water and the decreasing quality and quantity of available raw water. Moreover, a negative impact of climate change on freshwater resources is expected. Recent advances in molecular detection technologies for bacterial pathogens in drinking water bear the promise in improving the safety of drinking water supplies by precise detection and identification of the pathogens. More importantly, the array of molecular approaches allows understanding details of infection routes of waterborne diseases, the effects of changes in drinking water treatment, and management of freshwater resources.     

Survival and multiplication of Legionella pneumophila in municipal drinking water systems

Studies were conducted to investigate the survival and multiplication of Legionella spp. in public drinking water supplies. An attempt was made, over a period of several years, to isolate legionellae from a municipal system. Sampling sites included the river water supply, treatment plant, finished water reservoir system, mains, and distribution taps. Despite the use of several isolation techniques, Legionella spp. could not be detected in any of the samples other than those collected from the river. It was hypothesized that this was due to the maintenance of a chlorine residual throughout the system. To investigate the potential for Legionella growth, additional water samples, collected from throughout the system, were dechlorinated, pasteurized, and inoculated with Legionella pneumophila. Subsequent growth indicated that many of these samples, especially those collected from areas affected by an accumulation of algal materials, exhibited a much greater ability to support Legionella multiplication than did river water prior to treatment. Chemical analyses were also performed on these samples. Correlation of chemical data and experimental growth results indicated that the chemical environment significantly affects the ability of the water to support multiplication, with turbidity, organic carbon, and certain metals being of particular importance. These studies indicate that the potential exists for Legionella growth within municipal systems and support the hypothesis that public water supplies may contaminate the plumbing systems of hospitals and other large buildings. The results also suggest that useful methods to control this contamination include adequate treatment plant filtration, maintenance of a chlorine residual throughout the treatment and distribution network, and effective covering of open reservoirs.     

城市供水系统对水中真菌数量和群落结构的影响

【背景】对于饮用水中的微生物污染,绝大多数研究集中在细菌、病毒及原虫和蠕虫。由于真菌中包含多种潜在致病菌,应当引起人们的关注。【目的】研究城市供水系统中真菌数量、群落组成变化及可能存在的潜在致病真菌。【方法】利用MEA和RB两种培养基,对供水系统中的原水和两个水厂净水工艺过程及不同供水模式用户龙头水样进行培养法计数统计。提取上述样本总DNA,并应用Illumina MiSeq平台进行ITS1区高通量测序。【结果】从15个样本中共获得有效序列579 470条,1 260个OTU,包含8个门26个纲67个目228个属的真菌。门水平上子囊菌门真菌为供水系统优势真菌,属水平上不同样本存在差异,但曲霉属和枝顶孢属真菌在所有样本中均存在;培养法和高通量测序结果共同显示,活性炭过滤出水真菌数量和物种丰富度均较前一工艺有所上升;氯化消毒对真菌数量、物种多样性及物种组成影响显著;经过供水管网输配和二次供水设施后,用户龙头水样本真菌数量和物种丰富度明显高于出厂水。【结论】供水系统中的优势真菌为子囊菌门(Ascomycota),该门真菌可穿透净水工艺过程的多级屏障;水厂净水工艺能有效去除水中可培养真菌,生物活性炭过滤工艺能够影响真菌数目及物种多样性;供水管网及二次供水设施是末端饮用水中真菌污染的重要来源;供水系统中存在潜在致病真菌。     

饮用水系统硝化微生物分布规律、环境影响因素及调控应用的研究进展

硝化微生物广泛存在于饮用水系统中。水处理过程中,硝化微生物对含氮污染物的去除有突出贡献;而输配水过程中,硝化微生物会加剧消毒剂氯胺的降解,造成一系列饮用水微生物安全问题。本文介绍了常用硝化微生物检测方法,综述了硝化微生物在滤池、市政主管网、二次供水系统中的分布特征和规律,分析了环境因子及工程条件对硝化微生物的影响机制,探讨了硝化微生物强化应用及管控的实际工程措施,展望了未来饮用水系统中硝化微生物的研究重点与应用前景。     

Poor efficacy of residual chlorine disinfectant in drinking water to inactivate waterborne pathogens in distribution systems.

To evaluate the inactivating power of residual chlorine in a distribution system, test microorganisms (Escherichia coli, Clostridium perfringens, bacteriophage phi-X 170, and poliovirus type 1) were added to drinking water samples obtained from two water treatment plants and their distribution system. Except for Escherichia coli, microorganisms remained relatively unaffected in water from the distribution systems tested. When sewage was added to the water samples, indigenous thermotolerant coliforms were inactivated only when water was obtained from sites very close to the treatment plant and containing a high residual chlorine concentration. Clostridium perfringens was barely inactivated, suggesting that the most resistant pathogens such as Giardia lamblia, Cryptosporidium parvum, and human enteric viruses would not be inactivated. Our results suggest that the maintenance of a free residual concentration in a distribution system does not provide a significant inactivation of pathogens, could even mask events of contamination of the distribution, and thus would provide only a false sense of safety with little active protection of public health. Recent epidemiological studies that have suggested a significant waterborne level of endemic gastrointestinal illness could then be explained by undetected intrusions in the distribution system, intrusions resulting in the infection of a small number of individuals without eliciting an outbreak situation.     

Implications of biofilm-associated waterborne Cryptosporidium oocysts for the water industry

Waterborne Cryptosporidium has been responsible for drinking water-associated disease outbreaks in a number of developed countries. As a result of the resistance of Cryptosporidium to chlorine, which is typically applied as a final barrier to protect the quality of distributed drinking water, current management practices are focused on source-water management and water treatment as ways of preventing Cryptosporidium from entering drinking-water supplies. In the event that treatment barriers fail, surprisingly little is known of the fate of oocysts once they enter a distribution system. To assess properly the risks of waterborne Cryptosporidium, a more thorough understanding of the fate of oocysts in water distribution systems, with emphasis on Cryptosporidium-biofilm interactions, is required.     

Detection and surveillance of waterborne protozoan parasites

The majority of the world's population still live without access to healthy water and the contamination of drinking water with protozoan pathogens poses a serious threat to millions of people in the developing world. Even in the developed world periodic outbreaks of diarrhoeal diseases are caused by the protozoan parasites Cryptosporidium sp., Giardia duodenalis and Entamoeba histolytica. Thus, surveillance of drinking water is imperative to minimize such contaminations and ensure continuous supplies of healthy water world-wide. This article reviews the progress in technology for detection and surveillance of these important waterborne parasites.     

Contamination of Groundwater Systems in the US and Canada by Enteric Pathogens, 1990–2013: A Review and Pooled-Analysis

Background

Up to 150 million North Americans currently use a groundwater system as their principal drinking water source. These systems are a potential source of exposure to enteric pathogens, contributing to the burden of waterborne disease. Waterborne disease outbreaks have been associated with US and Canadian groundwater systems over the past two decades. However, to date, this literature has not been reviewed in a comprehensive manner.

Methods and Principal Findings

A combined review and pooled-analysis approach was used to investigate groundwater contamination in Canada and the US from 1990 to 2013; fifty-five studies met eligibility criteria. Four study types were identified. It was found that study location affects study design, sample rate and studied pathogen category. Approximately 15% (316/2210) of samples from Canadian and US groundwater sources were positive for enteric pathogens, with no difference observed based on system type. Knowledge gaps exist, particularly in exposure assessment for attributing disease to groundwater supplies. Furthermore, there is a lack of consistency in risk factor reporting (local hydrogeology, well type, well use, etc). The widespread use of fecal indicator organisms in reported studies does not inform the assessment of human health risks associated with groundwater supplies.

Conclusions

This review illustrates how groundwater study design and location are critical for subsequent data interpretation and use. Knowledge gaps exist related to data on bacterial, viral and protozoan pathogen prevalence in Canadian and US groundwater systems, as well as a need for standardized approaches for reporting study design and results. Fecal indicators are examined as a surrogate for health risk assessments; caution is advised in their widespread use. Study findings may be useful during suspected waterborne outbreaks linked with a groundwater supply to identify the likely etiological agent and potential transport pathway.     

Genotypes of Cryptosporidium from Sydney water catchment areas

AIMS: Currently cryptosporidiosis represents the major public health concern of water utilities in developed nations and increasingly, new species and genotypes of Cryptosporidium are being identified in which the infectivity for humans is not clear. The complicated epidemiology of Cryptosporidium and the fact that the majority of species and genotypes of Cryptosporidium cannot be distinguished morphologically makes the assessment of public health risk difficult if oocysts are detected in the raw water supplies. The aim of this study was to use molecular tools to identify sources of Cryptosporidium from the Warragamba catchment area of Sydney, Australia. METHODS AND RESULTS: Both faecal and water samples from the catchment area were collected and screened using immunomagnetic separation (IMS) and immunofluorescence microscopy. Samples that contained Cryptosporidium oocysts were genotyped using sequence and phylogenetic analysis of the 18S rDNA, and the heat-shock (HSP-70) gene. Analysis identified five Cryptosporidium species/genotypes including C. parvum (cattle genotype), C. suis, pig genotype II, the cervid genotype and a novel goat genotype. CONCLUSIONS: Monitoring and characterization of the sources of oocyst contamination in watersheds will aid in the development and implementation of the most appropriate watershed management policies to protect the public from the risks of waterborne Cryptosporidium. SIGNIFICANCE AND IMPACT OF THE STUDY: This study has shown that quantification by IMS analysis can be combined with the specificity of genotyping to provide an extremely valuable tool for assessing the human health risks from land use activities in drinking water catchments.     

Intelligent infrastructure for sustainable potable water: a roundtable for emerging transnational research and technology development needs

PROBLEM STATEMENT: Recent commercial and residential development have substantially impacted the fluxes and quality of water that recharge the aquifers and discharges to streams, lakes and wetlands and, ultimately, is recycled for potable use. Whereas the contaminant sources may be varied in scope and composition, these issues of urban water sustainability are of public health concern at all levels of economic development worldwide, and require cheap and innovative environmental sensing capabilities and interactive monitoring networks, as well as tailored distributed water treatment technologies. To address this need, a roundtable was organized to explore the potential role of advances in biotechnology and bioengineering to aid in developing causative relationships between spatial and temporal changes in urbanization patterns and groundwater and surface water quality parameters, and to address aspects of socioeconomic constraints in implementing sustainable exploitation of water resources. WORKSHOP OUTCOMES: An interactive framework for quantitative analysis of the coupling between human and natural systems requires integrating information derived from online and offline point measurements with Geographic Information Systems (GIS)-based remote sensing imagery analysis, groundwater-surface water hydrologic fluxes and water quality data to assess the vulnerability of potable water supplies. Spatially referenced data to inform uncertainty-based dynamic models can be used to rank watershed-specific stressors and receptors to guide researchers and policymakers in the development of targeted sensing and monitoring technologies, as well as tailored control measures for risk mitigation of potable water from microbial and chemical environmental contamination. The enabling technologies encompass: (i) distributed sensing approaches for microbial and chemical contamination (e.g. pathogens, endocrine disruptors); (ii) distributed application-specific, and infrastructure-adaptive water treatment systems; (iii) geostatistical integration of monitoring data and GIS layers; and (iv) systems analysis of microbial and chemical proliferation in distribution systems. IMPACT: This operational framework is aimed at technology implementation while maximizing economic and public health benefits. The outcomes of the roundtable will further research agendas in information technology-based monitoring infrastructure development, integration of processes and spatial analysis, as well as in new educational and training platforms for students, practitioners and regulators. The potential for technology diffusion to emerging economies with limited financial resources is substantial.     

A review of drinking-water-associated endotoxin,including potential routes of human exposure

In the past decade efforts have been made to reduce the formation of harmful disinfection byproducts during the treatment and distribution of drinking water. This has been accomplished in part by the introduction of processes that involve the deliberate encouragement of indigenous biofilm growth in filters. In a controlled environment, such as a filter, these biofilms remove compounds that would otherwise be available as disinfection byproduct precursors or support uncontrolled biological activity in distribution systems. In the absence of exposure to chlorinated water, most biofilm bacteria are gram negative and have an outer layer that contains endotoxin. To date, outbreaks of waterborne endotoxin-related illness attributable to contamination of water used in hemodialysis procedures have been only infrequently documented, and occurrences linked to ingestion or through dermal abrasions could not be located. However, a less obvious conduit, that of inhalation, has been described in association with aerosolized water droplets. This review summarizes documented drinking-water-associated incidents of endotoxin exposure attributable to hemodialysis and inhalation. Typical endotoxin levels in water and conditions under which substantial quantities can enter drinking water distribution systems are identified. It would appear that endotoxin originating in tap water can be inhaled but at present there is insufficient information available to quantify potential health risks.