Tracing Fecal Indicators and Pathogens in Rural Settings
Fecal contamination of the environment poses significant health risks, particularly in low- and middle-income countries where access to adequate water, sanitation, and hygiene (WASH) infrastructure is limited. Enteric pathogens, transmitted through the fecal-oral route, are a leading cause of diarrheal deaths globally. To address this challenge, researchers in Ethiopia are conducting the Exposure Assessment of Campylobacter Infections in Rural Ethiopia (EXCAM) project, which aims to identify potential sources of fecal contamination for infants during their first 1.5 years of life.
The EXCAM study collected over 1,300 samples from 76 households, including hand rinses, drinking and bathing water, food, soil, and breast milk. Researchers used Escherichia coli (E. coli) as an indicator organism to quantify fecal contamination. The results revealed that E. coli was ubiquitous within the selected households, with over 56% of samples testing positive across the study period. Notably, soil and hand samples had the highest prevalence (>53%) and concentrations (>2-log CFU) of E. coli, while other sample types, such as drinking water, had lower prevalence (51%) but at much lower concentrations (0.3-log CFU).
“Using E. coli as a surrogate, our study identified the mother’s hands and areola as reservoirs likely to be involved in frequent transmission of fecal contaminants to infants within rural Ethiopian households,” explained the researchers. This finding highlights the crucial role of caregiver hygiene in preventing infant exposure to harmful fecal pathogens.
Expanding the Toolkit: Emerging Indicators and Molecular Methods
While fecal indicator bacteria like E. coli have been used for over 150 years to assess water quality and associated health risks, researchers have long recognized their limitations. Fecal indicators cannot reliably distinguish between human and animal sources of fecal pollution, nor do they always correlate well with the presence of enteric pathogens.
To address these shortcomings, the field of water quality monitoring has embraced a range of alternative indicators and molecular detection methods. One promising approach is the use of host-associated microbes, such as members of the Bacteroidales order, which can help pinpoint the sources of fecal contamination. For example, the human-associated HF183 marker has become a widely adopted tool for identifying human fecal pollution.
Furthermore, the rapid advancement of molecular techniques, particularly quantitative PCR (qPCR) and digital PCR (dPCR), has revolutionized the detection and quantification of fecal indicators and pathogens. These methods can identify the presence of specific genetic targets, like bacterial and viral genes, within a matter of hours, providing a significant improvement in speed over traditional culturing techniques.
“Molecular methods, particularly PCR-based approaches, have advanced considerably in their selected targets and rigor, but have added complexity that may prohibit adoption for routine monitoring activities at this time,” noted the authors of a recent review.
Despite these advancements, challenges remain in the effective use of both traditional and alternative indicators. Ensuring reliable, reproducible results requires meticulous quality control measures, such as the use of multiple internal controls and reference materials. Additionally, the complex environmental dynamics that influence microbial fate and transport can make it difficult to establish consistent relationships between indicator organisms and human health risks.
Tracing Fecal Contamination through Viral Indicators
One emerging alternative indicator that has garnered significant attention is crAssphage, a recently discovered virus that infects bacteria in the human gut. A study by the Centers for Disease Control and Prevention (CDC) explored the potential of crAssphage as a marker for detecting human fecal contamination on environmental surfaces and hands during norovirus outbreaks.
The researchers tested stool samples, environmental swabs, and hand rinses collected from various settings, including cruise ships and long-term care facilities (LTCFs). Their findings were compelling:
- crAssphage was detected in 71.4% of norovirus outbreak stool samples, 48-68.5% of stool samples from healthy individuals, and 56.2% of environmental swabs and 60% of hand rinse samples.
- Sequence analysis of crAssphage strains revealed distinct genetic clusters, suggesting the potential to trace the source of fecal contamination.
- In LTCFs, identical crAssphage sequences found in stool and hand rinse samples of the same person indicated self-contamination, while different sequences suggested cross-contamination.
These results demonstrate the value of crAssphage as a tool for monitoring human fecal contamination of surfaces and hands, which can inform targeted cleaning and disinfection practices to prevent the spread of enteric pathogens.
Connecting Indicators to Health Risks
Ultimately, the goal of fecal indicator monitoring is to protect human health by assessing the potential for exposure to harmful enteric pathogens. However, the relationship between indicator organisms and human health risks is complex and highly variable, depending on factors such as the source of fecal pollution, environmental conditions, and exposure pathways.
Quantitative microbial risk assessment (QMRA) has emerged as a valuable approach for estimating the health implications of fecal contamination. QMRA models incorporate data on indicator concentrations, pathogen-indicator relationships, and dose-response functions to predict the likelihood of illness associated with different exposure scenarios.
Recent QMRA studies have provided important insights, such as:
- Threshold concentrations of human-associated markers (like HF183) that correspond to increased risk of illness are well above typical limits of detection, suggesting that these markers are highly likely to be present if pathogens pose a health hazard.
- Accounting for differential fate and transport of indicators and pathogens is crucial for accurate risk assessments, as the relative persistence of these organisms can significantly impact their co-occurrence and associated health risks.
While QMRA has advanced our understanding of indicator-health relationships, challenges remain in generalizing these findings across diverse environmental conditions and fecal sources. Continued research and validation of models will be essential to reliably connect fecal indicator data to meaningful assessments of public health risk.
Prioritizing Fecal Contamination Monitoring and Remediation
The widespread use of fecal indicators for water quality assessment has demonstrated their value as investigative tools, particularly in identifying sources of fecal pollution. As the toolkit of indicators and detection methods expands, water quality managers and public health professionals can leverage these tools to better understand and address fecal contamination in their communities.
In settings with ample resources and dedicated laboratory facilities, such as high-traffic recreational beaches, the implementation of rapid molecular monitoring approaches like qPCR or dPCR may provide timely warnings and insights to guide management decisions. For example, simultaneous testing of traditional indicators and human-associated markers could help pinpoint the sources of fecal pollution and prioritize remediation efforts.
However, in many resource-constrained settings, traditional culture-based methods for fecal indicator detection may remain the most feasible approach, complemented by predictive models that leverage factors like precipitation to estimate health risks. In these cases, the focus should be on ensuring the consistent, reliable application of well-established techniques rather than adopting more complex molecular methods that may exceed local capacity.
Regardless of the specific approach, the ultimate aim of fecal contamination monitoring should be to protect public health and guide interventions that improve access to safe water, sanitation, and hygiene. By leveraging the expanding toolkit of indicators and detection methods, water quality professionals can gather the evidence needed to advocate for targeted investments and policy changes that reduce the burden of enteric diseases in their communities.
Visit the Joint Action for Water website to learn more about community-driven initiatives and advocacy strategies for sustainable WASH solutions.
