can be attributed to contact with or ingestion of water while bathing [41]: gastrointestinal symptoms; eye infections; skin complaints; ear, nose, and throat infections;
and respiratory illnesses. They are the major source of evidence, in marine and fresh
water, that was used to define the criteria of the European Directive. In all studies a
non-bathing population is used as a reference; surveys are conducted to characterize
the bathing in great detail; the symptoms of swimmers and nonswimmers are queried
about 1 week after the bathing event (up to 3 weeks for one study). Despite efforts to
make the results as comparable as possible, differences may occur between studies.
They may concern the criteria used to define the severity of the disease and to qualify
bathing (one bath or one day at the beach, head immersed or not, duration of the bath,
etc.). In a randomized study, Wiedenmann et al. [43] enrolled participants to bathe
with a very precise protocol, which was not the case for other studies. Moreover, the
data (number of diseases) can be given for sites with different levels of contamination or can be classified as a function of the recorded contamination level in case of a
whole season survey at a single site; this is another source of discrepancy. Nevertheless, it is important to compare all these data to provide an integrated vision
because epidemiological studies are rare, in particular for fresh water.
In Fig. 8, we gathered data from selected studies, conducted in fresh water (lake
shores and rivers) in the USA and Europe, regarding the occurrence of highly
probable gastroenteritis. E. coli or fecal coliform concentrations were selected to
characterize water quality. Gastroenteritis is the most frequent disease reported
among swimmers, although not the most dangerous. Figure 8 shows the variability
that may exist between studies. However, above 200 E. coli per 100 mL (geometric
mean), all studies show an excess risk of gastroenteritis, while one study showed an
excess risk for concentrations as low as 10 E. coli per 100 mL.
The European Directive (2006/7/EC) defines a set of criteria based on E. coli and
intestinal enterococci concentrations to characterize the excellent, good, sufficient,
and poor status of bathing water (Table 1). More stringent criteria exist for marine
water. Although bathing can be authorized in water with sufficient quality, and even
a poor quality under specific circumstances, the directive recommends bringing as
many bathing areas in Europe as possible to a good water quality status.
Water quality monitoring is required during at least four successive bathing
seasons, and the data set to estimate water quality must include more than 16 samples. Bathing in an area with a poor status can be temporarily authorized, but it will
be closed after 5 years of poor status. The directive also demands “bathing water
profiles” to inform the public of the characteristics of the catchment, risks, and the
occurrence of short-term events that might require the temporary closure of the
bathing area and measures taken to limit risks (policies regarding spreading of
manure or sewage sludge, sewer system management, wastewater disinfection,
etc.). The bathing water profile should also inform on all additional potential risks
(cyanobacteria or algal blooms, motor water sports, etc.).
For areas with a high frequency of dangerous short-term events, the directive
allows disregarding no more than 15% of the samples with the highest concentrations before the estimation of the quality criteria. This imposes setting up
efficient management measures including surveillance, early warning systems, and
Bathing Activities and Microbiological River Water Quality in the Paris. . .
337
and respiratory illnesses. They are the major source of evidence, in marine and fresh
water, that was used to define the criteria of the European Directive. In all studies a
non-bathing population is used as a reference; surveys are conducted to characterize
the bathing in great detail; the symptoms of swimmers and nonswimmers are queried
about 1 week after the bathing event (up to 3 weeks for one study). Despite efforts to
make the results as comparable as possible, differences may occur between studies.
They may concern the criteria used to define the severity of the disease and to qualify
bathing (one bath or one day at the beach, head immersed or not, duration of the bath,
etc.). In a randomized study, Wiedenmann et al. [43] enrolled participants to bathe
with a very precise protocol, which was not the case for other studies. Moreover, the
data (number of diseases) can be given for sites with different levels of contamination or can be classified as a function of the recorded contamination level in case of a
whole season survey at a single site; this is another source of discrepancy. Nevertheless, it is important to compare all these data to provide an integrated vision
because epidemiological studies are rare, in particular for fresh water.
In Fig. 8, we gathered data from selected studies, conducted in fresh water (lake
shores and rivers) in the USA and Europe, regarding the occurrence of highly
probable gastroenteritis. E. coli or fecal coliform concentrations were selected to
characterize water quality. Gastroenteritis is the most frequent disease reported
among swimmers, although not the most dangerous. Figure 8 shows the variability
that may exist between studies. However, above 200 E. coli per 100 mL (geometric
mean), all studies show an excess risk of gastroenteritis, while one study showed an
excess risk for concentrations as low as 10 E. coli per 100 mL.
The European Directive (2006/7/EC) defines a set of criteria based on E. coli and
intestinal enterococci concentrations to characterize the excellent, good, sufficient,
and poor status of bathing water (Table 1). More stringent criteria exist for marine
water. Although bathing can be authorized in water with sufficient quality, and even
a poor quality under specific circumstances, the directive recommends bringing as
many bathing areas in Europe as possible to a good water quality status.
Water quality monitoring is required during at least four successive bathing
seasons, and the data set to estimate water quality must include more than 16 samples. Bathing in an area with a poor status can be temporarily authorized, but it will
be closed after 5 years of poor status. The directive also demands “bathing water
profiles” to inform the public of the characteristics of the catchment, risks, and the
occurrence of short-term events that might require the temporary closure of the
bathing area and measures taken to limit risks (policies regarding spreading of
manure or sewage sludge, sewer system management, wastewater disinfection,
etc.). The bathing water profile should also inform on all additional potential risks
(cyanobacteria or algal blooms, motor water sports, etc.).
For areas with a high frequency of dangerous short-term events, the directive
allows disregarding no more than 15% of the samples with the highest concentrations before the estimation of the quality criteria. This imposes setting up
efficient management measures including surveillance, early warning systems, and
Bathing Activities and Microbiological River Water Quality in the Paris. . .
337