1.1 Fecal Indicator Bacteria Monitoring in the USA
Recent monitoring data compiled annually across the USA shows that many
interior and coastal waters are chronically polluted with fecal indicator bacteria
(FIB) [7]. The situation has actually worsened in recent years along heavily
urbanized coastlines [8]. As an example, in 2006 FIB levels in US waters were
the highest in 17 years, with over 25,000 advisories and recreational closures
nationwide, 30 % higher than in 2004 [9]. The dry summer of 2007 was also a
problem, with 22,571 days of closings and advisories for US oceans, bays, and
Great Lakes beaches [10]. These examples are alarming, as high FIB concentrations
indicate unhealthy waters and cause economic losses to local communities [11,
12]. Advisories posted by state agencies for recreational waters are typically
covered by the news media and have a negative impact on the public perceptions
of water safety and the agencies responsible for protecting public health [13].
Many beach studies have demonstrated that direct contact with water and sand
contaminated with fecal pollution can result in gastrointestinal illnesses that can be
severe, especially for immunocompromised individuals [14–16]. Swimming, especially total immersion in recreational waters, is an activity that allows transmission
of waterborne pathogens by the fecal–oral route [17]. Although there are pathogens
from non-human sources that can be harmful to humans (e.g., livestock and
wildlife), the greatest risk of illness is fecal contamination from human sources,
which may contain enteric viruses and parasites not normally found outside of
human hosts [14]. Direct monitoring for waterborne human pathogens is impractical due to the wide variety of pathogens that might be present, low concentrations
that make detection difficult, and the high cost of laboratory analysis [18]. Instead,
water monitoring strategies target FIB, which were chosen based on their presence
in the feces of warm-blooded animals, low rates of survival and/or low natural
occurrence in extra-intestinal habitats, and their association with human pathogens
of concern [19]. Because these indicators of fecal contamination are found in the
intestines of all warm-blooded animals, they can be helpful in locating general
sources of pollution, but they are not useful in differentiating between environmental, agricultural, and human sources of pollution [20].
Water quality criteria based on FIB were originally adopted because epidemiological research linked increased swimmer illness to raw sewage discharges
[21]. Today most wastewater in the USA is treated to secondary standards, but
FIB, including DNA-based Enterococcus measurements, still indicates that many
waters are unhealthy as per epidemiological relationships [15]. While FIB are
legitimately the “gold standard” in food and potable water safety, they are imperfect
tracers for threats to public health from pathogen-containing fecal material in
environmental waters [22]. One reason for this is because culture-based assays
require 18–24 h incubation, during which contamination and field conditions can
change. To address this problem, newer culture-independent methods for quantitative PCR (qPCR) of Enterococcus spp. are now available that allow FIB measurements in 4–6 h [23]. However, a second challenge, related to using FIB as tracers, is
Microbial Source Tracking: Advances in Research and a Guide to Application
269
Recent monitoring data compiled annually across the USA shows that many
interior and coastal waters are chronically polluted with fecal indicator bacteria
(FIB) [7]. The situation has actually worsened in recent years along heavily
urbanized coastlines [8]. As an example, in 2006 FIB levels in US waters were
the highest in 17 years, with over 25,000 advisories and recreational closures
nationwide, 30 % higher than in 2004 [9]. The dry summer of 2007 was also a
problem, with 22,571 days of closings and advisories for US oceans, bays, and
Great Lakes beaches [10]. These examples are alarming, as high FIB concentrations
indicate unhealthy waters and cause economic losses to local communities [11,
12]. Advisories posted by state agencies for recreational waters are typically
covered by the news media and have a negative impact on the public perceptions
of water safety and the agencies responsible for protecting public health [13].
Many beach studies have demonstrated that direct contact with water and sand
contaminated with fecal pollution can result in gastrointestinal illnesses that can be
severe, especially for immunocompromised individuals [14–16]. Swimming, especially total immersion in recreational waters, is an activity that allows transmission
of waterborne pathogens by the fecal–oral route [17]. Although there are pathogens
from non-human sources that can be harmful to humans (e.g., livestock and
wildlife), the greatest risk of illness is fecal contamination from human sources,
which may contain enteric viruses and parasites not normally found outside of
human hosts [14]. Direct monitoring for waterborne human pathogens is impractical due to the wide variety of pathogens that might be present, low concentrations
that make detection difficult, and the high cost of laboratory analysis [18]. Instead,
water monitoring strategies target FIB, which were chosen based on their presence
in the feces of warm-blooded animals, low rates of survival and/or low natural
occurrence in extra-intestinal habitats, and their association with human pathogens
of concern [19]. Because these indicators of fecal contamination are found in the
intestines of all warm-blooded animals, they can be helpful in locating general
sources of pollution, but they are not useful in differentiating between environmental, agricultural, and human sources of pollution [20].
Water quality criteria based on FIB were originally adopted because epidemiological research linked increased swimmer illness to raw sewage discharges
[21]. Today most wastewater in the USA is treated to secondary standards, but
FIB, including DNA-based Enterococcus measurements, still indicates that many
waters are unhealthy as per epidemiological relationships [15]. While FIB are
legitimately the “gold standard” in food and potable water safety, they are imperfect
tracers for threats to public health from pathogen-containing fecal material in
environmental waters [22]. One reason for this is because culture-based assays
require 18–24 h incubation, during which contamination and field conditions can
change. To address this problem, newer culture-independent methods for quantitative PCR (qPCR) of Enterococcus spp. are now available that allow FIB measurements in 4–6 h [23]. However, a second challenge, related to using FIB as tracers, is
Microbial Source Tracking: Advances in Research and a Guide to Application
269