Journal of the Marine Biological Association of the United Kingdom, 2016, 96(1), 93 –100.
doi:10.1017/S0025315415002003
# Marine Biological Association of the United Kingdom, 2016
The association between marine bathing and
infectious diseases– a review
nicholas young1,2
1
University of Bristol, Bristol, UK, 2Public Health England, Exeter, UK
Worldwide, infectious diseases represent a leading cause of death and disability. Exposure to the ocean, whether through
recreation or occupation, represents a potentially significant, but poorly understood, source of infectious diseases in man.
This review describes the potential mechanisms whereby marine bathing could lead to infectious diseases in man. Sources
of pathogens in the marine environment are described, including human sewage, animal sources, fellow bathers and indigenous marine organisms. The epidemiological evidence for the association between marine bathing and infectious disease is presented, including a consideration of the differing relationship between faecal indicator bacteria levels and illness at point
source compared with non-point source settings. Estimating the burden of infectious disease is reliant on public health surveillance, both formal and informal, which is described from a UK perspective in this review. Potential emerging threats at the
marine–human interface are discussed, including infections caused by Shewanella and Vibrio bacteria, and the presence of
human pathogens in the marine environment that are resistant to antimicrobials.
Keywords: infectious disease, marine pollution, faecal indicator bacteria, emerging infections
Submitted 5 November 2015; accepted 6 November 2015
INTRODUCTION
Infectious diseases in man result from invasion by microbes
and subsequent injury, or, less commonly, through contact
with non-invasive microbial toxins (Spicer, 2008). Pathogenic
organisms, i.e. those capable of causing disease, range from
microscopic agents such as prions and viruses – incapable
of independent reproduction or prolonged survival –
through to bacteria, eukaryotic organisms like moulds, fungi
and larger protozoa, and then multicellular animals such as
helminths.
Worldwide, infectious diseases represent a leading cause of
death and disability, with over 3 million deaths from lower
respiratory infections and 1.5 million from diarrhoeal illnesses
in 2012 (World Health Organization, 2014); food and waterborne illnesses are estimated to kill 2.2 million people per year,
most of whom are children (World Health Organization,
2015a).
In the UK, the burden of infectious disease is lower
compared with less developed nations, but nonetheless still
significant. Campylobacter, the leading cause of bacterial
gastroenteritis in the UK, is estimated to affect 500,000
people per year leading to 80,000 primary care consultations.
Norovirus, the leading cause of viral gastroenteritis, is estimated to cause 3 million episodes of illness annually at a significant financial cost to health services and wider society
(Tam et al., 2012). In 2012 in England, there were 800 laboratory reports of E. coli 0157, a serious gastrointestinal bacterial
infection that can lead to disability and even death (Public
Health England, 2014a).
Corresponding author:
N. Young
Email: nick.young@phe.gov.uk
With estimates of more than a million bacteria present per
mL of seawater, and 10– 100 times as many viral particles, the
ocean represents a potentially significant, but poorly understood, source of infectious diseases in man; and of the estimated 1 billion marine bacterial species only a small
proportion have been characterized (Thomas & Bowers,
2012). Human exposure to marine micro-organisms can
occur as a result of bathing, recreation, the food chain and
occupation. Nonetheless, any potential risks from infectious
disease need to be balanced against the benefits of exposure
to the marine environment, including as a source of food
and the demonstrable effects on physical and mental wellbeing (Depledge & Bird, 2009).
This review will present the theoretical basis of infectious
disease transmission, and how it relates to marine bathing;
describe sources of marine pathogens; and present evidence
to support associations with disease. Additionally, infectious
disease surveillance and the risks of emerging infections
related to marine bathing will be considered. Finally public
health measures informed by evidence and research priorities
to reduce the burden of disease will be presented.
INFECTIOUS DISEASE
TRANSMISSION
For a host to become infected with an infectious disease, a
sequence of events – referred to as the Chain of Infection –
needs to occur (United States Centers for Disease Control &
Prevention, 2015). A pathogenic organism leaves its reservoir
through a portal of exit, reaches a host via a mode of transmission, entering through a portal of entry to cause infection and
disease in a susceptible host. Infection control strategies are
focused on breaking one or more links in the chain.
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Potential reservoirs for marine bathing-related infection
include seawater – with or without anthropogenic input (Kay
et al., 1994; Wade et al., 2003; Tolba et al., 2008; Vignier et al.,
2013), beach sand and sediment (Solo-Gabriele et al., 2000;
Beversdorf et al., 2007; Yamahara et al., 2007), zooplankton
(Huq et al., 1990), fellow bathers (Plano et al., 2011) and
animals (Wang et al., 2010). Gastrointestinal pathogens, for
example norovirus and E. coli, leave human and animal hosts
respectively through faeces (Ihekweazu et al., 2005), whereas
skin shedding of methicillin-resistant Staphylococcus aureus
may potentially increase the risk to fellow bathers (Tolba et al.,
2008; Plano et al., 2011, 2013). The mode of transmission for
gastrointestinal pathogens is faeco-oral – once organisms
leave an infected host subsequent ingestion can lead to infection.
In addition to faeco-oral transmission, marine bathers may
become ill through inhalation of pathogens in marine aerosols
– leading to respiratory tract disease – and through direct
contact with skin, ears and eyes.
Numerous host factors determine susceptibility to marinederived pathogens and the severity of any subsequent illnesses.
Breaches of innate defences (e.g. skin ulcers and penetrating
trauma) increase the risk of bathing-related infection (Vignier
et al., 2013; Janda & Abbott, 2014); subsequent disease risk
depends on age (Lepesteur et al., 2006; Wade et al., 2008);
co-morbid conditions such as diabetes mellitus and impaired
immunity (Frank et al., 2006; Vignier et al., 2013); and the presence of immunity from previous infection (Prieto et al., 2001) or
vaccination. The ability of an organism to cause disease, and the
subsequent severity, is termed ‘virulence’; some pathogens, such
as noroviruses, generally cause mild self-limiting illness, whereas
ingestion of a limited number of Verotoxin-producing E. coli can
lead to severe illness and even death.
The development of infectious disease in man is determined
by complex interactions between the host, pathogens and the
environment (Scholthof, 2007). This interaction is apparent in
marine bathing; host behaviour is associated with the illness,
with activities that increase duration of exposure, and swallowing of water increasing risk (Wade et al., 2003; Papastergiou
et al., 2012; Harder-Lauridsen et al., 2013); increased risk is suggested with surfing activities, diving and athletic events (Bradley
& Hancock, 2003; Wade et al., 2003; Schijven & de Roda
Husman, 2006; Harder-Lauridsen et al., 2013). Environmental
conditions such as eutrophication, sunlight and rainfall will all
determine the growth and fate of micro-organisms and so alter
the probability of disease (Yau et al., 2014). In a single study,
swallowing water was a risk factor for gastrointestinal illness
only in the presence of high groundwater discharge and low
solar radiation (Yau et al., 2014).
Bradley & Hancock (2003) elegantly demonstrated an
example of the complex host-pathogen-environment relationship in marine bathing. During meteorological conditions with
greater wave height; this is associated with higher numbers of
bathers participating in high risk activity (surfing) and where
levels of faecal indicator bacteria were significantly higher than
during calm weather (Bradley & Hancock, 2003).
SOURCES AND SURVIVAL OF
PATHOGENS IN THE MARINE
ENVIRONMENT
The predominant sources of human pathogens in the marine
environment in the UK are considered to be from: human
sewage, whether through poorly connected domestic sewers
or combined sewage outflows or treated waste; agricultural
run-off; urban area run-off; and animal and bird faeces
(Environment Agency, UK, 2014).
Faecal indicator bacteria (FIB) are a limited number of
organisms (typically Coliforms, E. coli, faecal Streptococci
and Enterococci) used as markers for the presence of sewage
containing human faeces. Not necessarily pathogenic per se,
FIB are used as a proxy measure for the vast number of pathogens potentially present in human waste (Wade et al., 2008).
Measurement of these organisms is undertaken widely and
their association with disease described in areas with point
sources of microbial pollution, but the discharge of pathogenic
organisms into the sea and their persistence, survival and subsequent virulence are poorly understood. Microbial source
tracking has demonstrated potential in identifying the
sources of pathogen in the marine environment (Rusinol
et al., 2014).
Current established methods for measuring FIB are based
on culturing organisms; therefore requiring a minimum of
24 –36 h to provide results. Novel molecular methods, specifically quantitative Polymerase Chain Reaction (qPCR), can
provide measures of microbial contamination in bathing
waters within a few hours and therefore have the potential
to inform short-term public health interventions such as
beach closures (Oliver et al., 2014). There is some epidemiological evidence linking qPCR measures of FIB and illness
(Wade et al., 2010), but further studies would be required if
slower, culture-based measures are to be replaced (Oliver
et al., 2014).
Many human pathogens have been identified in seawater
and the marine environment, including: viruses – adenovirus
(Pina et al., 1998; Jiang & Chu, 2004; Colford et al., 2007), noroviruses (Victoria et al., 2010), enteroviruses (Pina et al., 1998;
Jiang & Chu, 2004) and hepatitis A (Jiang & Chu, 2004); bacteria – S. aureus (including methicillin-resistant Staphlylococcus
aureus (MRSA)) (Plano et al., 2013), Bacteroides spp. (Colford
et al., 2007), Clostridia (Wade et al., 2010), also demonstrated
in sand (Heaney et al., 2012; Plano et al., 2013), Pseudomonas
spp. (Khan et al., 2010); protozoa – Cryptosporidia in seawater (Fayer et al., 1998) and giardia in the faeces of marine
mammals (Measures & Olson, 1999).
Salmonella bacteria have been found in small numbers of
samples of bathing water classified using FIB measurements
as excellent by European bathing water standards;
Salmonella levels were positively correlated with FIB levels
(Efstratiou & Tsirtsis, 2009).
In addition to pathogens from sewage, run-off and animal
sources, there is potential for colonized individuals to infect
others with potentially pathogenic organisms. Under experimental conditions mimicking marine bathing, individuals
can release 105 –106 S. aureus per 15 min immersion; with
15 –20% of isolates being resistant (MRSA), capable of
causing serious soft-tissue infections (Plano et al., 2011).
Plano et al. (2013) demonstrated a correlation between
bather density and concentrations of S. aureus in sub-tropical
recreational waters, with levels of 2–780 colony forming units
(CFUs) per mL (Plano et al., 2013). Experimental evidence
suggests that S. aureus may be able to persist in seawater for
several days (Fujioka & Unutoa, 2006). Further experimental
work suggests that individuals shed in the region of 1
million enterococci per bathing episode (Elmir et al., 2007,
2009) and potentially up to the same number of
the association between marine bathing and infectious diseases
Bacteroidales – a potential indicator of human contamination
(Elmir et al., 2009).
In addition to faecal pathogens from external sources, indigenous marine bacteria are capable of causing disease in
humans; examples include Vibrio spp. (Huq et al., 1990;
Andersson & Ekdahl, 2006; Frank et al., 2006; Kushawaha
et al., 2010), Shewanella (Dominguez et al., 1996; Vignier
et al., 2013; Srinivas et al., 2015) and mycobacteria (Cheung
et al., 2010). In a review of 171 patients from a coastal area
of South Korea diagnosed with necrotizing fasciitis – a potentially fatal soft-tissue infection – marine bacteria were considered to be the causal pathogen in two-thirds of cases (Park
et al., 2009).
SURVEILLANCE OF INFECTIOUS
DISEASES
Public health surveillance is defined as “the continuous, systematic collection, analysis and interpretation of healthrelated data needed for the planning, implementation, and
evaluation of public health practice” (World Health
Organization, 2015b); robust systems are fundamental to
public health practice. Surveillance data are used to identify
trends, both short- and long-term; identify disease outbreaks
and emerging threats; provide hypotheses of causal associations; and provide policymakers with evidence used to prioritize resources. Surveillance can take many forms – both
formal and informal – and recent advances in genomics
have the potential to provide public health authorities with
additional information with which to identify previously
elusive shared exposures among cases of infectious disease
(Dallman et al., 2015).
Many European countries have well-developed infectious
disease surveillance systems; as in many countries, in the
UK registered medical practitioners are legally required to
notify certain infectious diseases – whether suspected or confirmed. Notifiable diseases listed in the UK Public Health
(Control of Disease) Act 1984 include several relevant to
marine exposure, including Verotoxin-producing E. coli
(Ihekweazu et al., 2005), Vibrio cholerae (Huq et al., 1990)
and Campylobacter spp. (Harder-Lauridsen et al., 2013).
Despite robust systems being in place, cases reported represent only a small proportion of persons infected, particularly
if their illness is mild and self-limiting; based on data from
UK primary care, it is estimated that for every case of gastrointestinal infection reported to national surveillance, there are
10 primary care consultations and 147 cases in the community
(Tam et al., 2012). In addition to physician reporting, there is
a reporting system which collects laboratory confirmed infections to public health; as described previously, this will only
detect the tip of the ‘clinical iceberg’ in milder disease, but
would be expected to detect a larger proportion of more
severe infection such as Verotoxin-producing E. coli that
can cause bloody diarrhoea and haemolytic-uraemic syndrome (Heymann, 2008).
Formal notification provides only part of the information
used to monitor infectious diseases in the UK; many other
sources of data are available. In England a syndromic surveillance team analyses health data from several sources in realtime, allowing rapid dissemination of trend data to identify
emerging threats (Public Health England, 2014b); syndromes
pertinent to marine exposure include gastroenteritis and acute
respiratory infection. Syndromic surveillance has demonstrated research utility in the field of environmental and
human health (Elliot et al., 2013).
In addition to formal surveillance by public health authorities, additional sources of data can provide insights into the
emergence of infectious disease outbreaks, particularly in
areas where robust systems are absent. In 2003, the World
Health Organization (WHO) was alerted to the emergence
of the SARS epidemic in Guangdong Province, China by an
early warning tool searching global media reports; this
method detected the emergence of SARS significantly in
advance of formal surveillance (Heymann & Rodier, 2004;
Keller et al., 2009). In additional to public health bodies, stakeholders (including charities), have set up surveillance
systems. For example, Surfers Against Sewage (SAS), a UK
environmental charity, collects reports of illness among
bathers/surfers, and has conducted a self-reported beach
user health survey in collaboration with the European
Centre for Environment and Human Health (ECEHH;
http://www.ecehh.org) in the UK; there is an antecedent to
the use of online surveys to record water-associated illness
(Turbow et al., 2008).
Identifying infectious disease outbreaks related to recreational use of the marine environment poses challenges as
exposed populations quickly disperse, particularly tourists.
In response to notified cases of infectious diseases in the
UK, questionnaires are administered in an attempt to identify
shared exposures and therefore potential sources of disease;
for example, persons diagnosed with Verotoxin-producing
E. coli in England are specifically asked about any site and
type of exposure to seawater. In 2006, an outbreak of seven
cases of E. coli was identified associated with playing in the
same beach stream (Ihekweazu et al., 2005). By their nature,
diseases with longer and less precise incubation periods,
such as some types of viral hepatitis, often identify a greater
number of potential causal exposures; apparent clustering of
cases related to a single exposure therefore becomes harder
to identify.
The use of questionnaire data to identify epidemiological
links requires considerable resource and cooperation from
cases, often introducing additional delay in the process of
identifying common exposures. Novel molecular techniques,
such as whole-genomic sequencing, are beginning to provide
opportunities to rapidly identify common exposures among
populations that are temporally and geographically dispersed
(Dallman et al., 2015). Nevertheless this approach may be
negated by outbreaks caused by several pathogens released following a particular environmental or anthropogenic event
(Harder-Lauridsen et al., 2013).
EVIDENCE FOR THE ASSOCIATION
BETWEEN MARINE BATHING AND
INFECTIOUS DISEASE
Numerous studies have demonstrated an increased risk of
gastrointestinal illness (Corbett et al., 1993; Kay et al., 1994;
Colford et al., 2007; Wade et al., 2008; Fleisher et al., 2010;
Papastergiou et al., 2012; Yau et al., 2014), ear infections
(Corbett et al., 1993; Fleisher et al., 1996; Papastergiou et al.,
2012; Wade et al., 2013), eye infections (Corbett et al., 1993;
Fleisher et al., 1996; Papastergiou et al., 2012), respiratory
illness (Corbett et al., 1993; Prieto et al., 2001; Fleisher et al.,
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2010; Papastergiou et al., 2012) and skin complaints (Prieto
et al., 2001; Colford et al., 2007; Fleisher et al., 2010) associated with marine swimming – typically defined as head
immersion – compared with non-swimmers. The overall incidence of any illness among swimmers in historical studies
includes 2– 3% (Papastergiou et al., 2012), 4.5 –6.1%
(Colford et al., 2007), 7.5% (Prieto et al., 2001), 14.8% (Kay
et al., 1994) and 24% (Corbett et al., 1993), with the relative
risk of gastrointestinal illness compared with non-swimmers
quantified at approximately 1.5 times higher (Balarajan
et al., 1991; Corbett et al., 1993; Kay et al., 1994), double
(Fleisher et al., 2010; Arnold et al., 2013), and up to 3.6
times greater (Papastergiou et al., 2012).
The association between levels of FIB and illness among
swimmers has been studied. Kay et al. (1994) demonstrated
an association between any illness and faecal streptococci
counts measured at chest level, suggesting a threshold level
of 32 CFUs per 100 mL below which there is no increased
risk (Kay et al., 1994). In a systematic review and
meta-analysis, Wade et al. (2003) estimated that for a log10
unit increase in enterococci, the risk of gastrointestinal
illness was increased by 1.34 times; additionally noting an
association between enterovirus and illness in a small
number of studies (Wade et al., 2003). The presence of any
illness following marine bathing has been shown in a single
study to be more closely associated with mean coliform
counts than faecal streptococci levels (Corbett et al., 1993).
Furthermore, levels of enterococci in sand are positively associated with gastrointestinal illness among beachgoers digging
or buried in sand (Heaney et al., 2012).
Despite evidence of association between FIB levels and
illness, this is not a consistent finding. Colford et al. (2007)
demonstrated higher rates of gastrointestinal and skin symptoms among a cohort of swimmers compared with nonswimmers, but no association between enterococci or faecal
coliform levels and reported illness. Likewise, the BEACHES
study found elevated incidence of gastrointestinal, acute
febrile and skin illness in bathers compared with those nonbathing bathers under sub-tropical conditions, the only association with FIB levels was between enterococci levels and skin
illness (Fleisher et al., 2010). Both studies were carried out at
beaches with a non-point source run-off, suggesting that
where high exposure to an output of human waste is not the
predominant source of pathogens traditional FIB may not
be predictive of human health impacts (Colford et al., 2007).
Microbiological testing conducted in areas of California
urban run-off have demonstrated a lack of association
between adenovirus, a potential viral pathogen, and FIB
levels (Jiang et al., 2001).
Under the European Union revised Bathing Water
Directive (2006/7/EC), coastal water is classified as ‘excellent’
and awarded ‘blue flag status’ if E. coli are predominately
below 250 per 100 mL and intestinal enterococci below 100
per 100 mL. Among bathers at sites with demonstrable excellent water quality by EU standards, there was still evidence of
increased gastrointestinal, respiratory, eye and ear infections
compared with non-bathers; with 3% of bathers having
gastroenteritis compared with 0.7% of non-bathers in the 10
days following exposure (Papastergiou et al., 2012). Furthermore, it is estimated that at the threshold for excellent
bathing water quality for enterococci by European standards,
it would be expected that 2.5 – 4.0% of bathers would develop
gastrointestinal illness (Saliba & Helmer, 1990). Estimates
suggest that 71% of gastrointestinal episodes in Southern
California occur when the water quality is considered safe
for bathing (Brinks et al., 2008), indicating that a ‘prevention
paradox’ may exist – most cases of illness associated with
marine bathing arise from the lowest risk exposure, but
higher numbers of people exposed; this observation has implications for preventative strategies aimed at reducing the
burden of disease.
The majority of epidemiological studies investigating the
associations between marine bathing and illness have relied
on self-reporting to define cases; however, there are clearly
limitations to this approach. Bathers may be more likely to
report symptoms if they believe they have had an exposure,
such as head immersion, and in retrospective studies ‘recall
bias’ may lead to increased reporting of events – such as swallowing water – in persons who have become unwell. A limited
number of studies have attempted to obtain microbiological
confirmation of the cause of illness; an association between
exposure to seawater and confirmed staphylococcal skin infections has been shown (Charoenca & Fujioka, 1995). Following
heavy rainfall in Copenhagen, 42% of competitors in a
sea-swimming event reported gastrointestinal illness; competitors who submitted stool samples had confirmed illness as a
result of various pathogens including Campylobacter jejuni,
Giardia lamblia and diarrheagenic E. coli. However, microbiological testing of the vast majority of stool samples submitted
by competitors did not reveal any pathogens, suggesting a
viral cause for illness in these competitors as very few specimens were tested for viruses (Harder-Lauridsen et al., 2013).
Simulation models incorporating bathing water quality
have estimated a considerable burden of disease related to
bathing in coastal waters in Southern California, with
689,000 to over 4 million episodes of gastrointestinal disease
and 693,000 episodes of respiratory illness among the 100
million visitors per year (Brinks et al., 2008). Marine-bathing
associated earache in the United States has the potential to
result in 260,000 visits to the doctor, and direct health costs
of nearly US$60 million (Wade et al., 2013).
EMERGING INFECTIOUS DISEASES
AND THE MARINE INTERFACE
The term ‘emerging infectious diseases’ is used to describe: the
emergence of novel or evolved pathogens, the spread of infections to new populations or geographic areas, or an increased
threat resulting from antimicrobial resistance to previously
treatable conditions (United States Centers for Disease
Control & Prevention, 2014). Notable recent emerging
human infectious diseases include avian influenza, Severe
Acute Respiratory Syndrome (SARS) and Middle East respiratory syndrome coronavirus (MERS Co-V); all of which are
considered to have emerged from hosts in the natural environment (Heymann, 2008). Examples of zoonotic (transferred
between animals and humans) marine-related infections
exist; a classical example being vibrio cholerae existing as a
commensal organism in zooplankton, primarily copepods,
conceivably leading to epidemics of cholera among humans
(Huq et al., 1990).
Shewanella are bacteria that are found in marine environments worldwide (Holt et al., 2005); over 50 species of this
genus have been identified but recent developments in speciation have led to the identification of Shewanella putrefaciens
the association between marine bathing and infectious diseases
and Shewanella algae as potential emerging human pathogens
(Goyal et al., 2011; Vignier et al., 2013; Janda & Abbott, 2014).
Shewanella infection, of which 80% are caused by S. algae, can
lead to skin and soft tissue infection, septicaemia, ear infections and death (Goyal et al., 2011; Vignier et al., 2013;
Janda & Abbott, 2014; Srinivas et al., 2015). Case series of
Shewanella infection, with case-fatality rates of 20 –25%,
have been reported in warmer climates, including
Martinique and India (Vignier et al., 2013; Srinivas et al.,
2015); although a systematic review by Vignier et al. (2013)
identified cases from northern Europe, including France,
Denmark and the UK (Vignier et al., 2013). The majority
(Vignier et al., 2013) or all (Srinivas et al., 2015) of
Shewanella cases in reported series had skin breaks or penetrating injury providing a portal of entry; a risk factor often
identified along with chronic health conditions with potential
immunosuppression such as diabetes mellitus in people
infected with marine indigenous bacteria (Gomez et al.,
2003; Frank et al., 2006; Aigbivbalu & Maraqa, 2009;
Cheung et al., 2010). Multidrug resistance has been demonstrated in some isolates of Shewanella (Holt et al., 2005).
During a notable warm summer in 1994 in Denmark,
S. algae was isolated from ear swabs from 67 patients mostly
aged between 3 –15 years; most of the patients had symptoms
of acute or chronic otitis (52%) or a non-specific aural discharge; S. algae was isolated from bathing sites in the same
area where cases were identified (Holt et al., 1997).
Vibrios are bacteria found in estuarine and salt water environments; species that cause illness in man include V. cholerae
– causing gastrointestinal illness (including cholera with
toxin-producing forms); V. parahaemolyticus – gastroenteritis; V. vulnificus – skin infections, septicaemia and death;
and V. alginolyticus – wound, ear and eye infections
(Spicer, 2008). In 2006, a notably warm summer in Europe
when sea temperatures across much of the Baltic Sea were
.208C, cases of V. vulnificus and non-toxin-producing
V. cholerae were reported in Germany and Sweden, respectively; cases of vibrio infection were also reported in
Denmark in the same year including a fatality associated
with V. vulnificus – all cases identified in the three countries
had bathed in the Baltic Sea (Frank et al., 2006). Vibrio spp.
were identified widely in the Baltic Sea in July and August
2006 (Frank et al., 2006) and have since also been found to
be common in Dutch waters (Schets et al., 2011); cases of
V. alginolyticus were detected in people bathing in Dutch
Waters of the North Sea in 2006 (Schets et al., 2006). The pandemic strain of V. parahaemolyticus has recently been identified in UK waters for the first time (Powell et al., 2013); it has
been suggested that, as patterns of infection with Vibrio spp.
are associated with climate trends, increasing sea temperatures
have the potential to increase the range and burden of related
disease. Furthermore, following Hurricane Katrina, an
extreme weather event in 2005, there were five reported
deaths from vibrio-related wound infections in persons from
affected states (United States Centers for Disease Control &
Prevention, 2005). Robust surveillance systems will be
required to detect emerging trends (Baker-Austin et al., 2010).
Antimicrobial resistance (AMR) is a major emerging global
public health threat that challenges our ability to treat
common infectious diseases; resistant strains can emerge
and disseminate worldwide resulting in a highly significant
disease burden (World Health Organization, 2015c).
Escherichia coli resistant to antibiotics, notably third-
generation cephalosporins, have been demonstrated in
coastal waters across England and Wales, posing a potential
risk to recreational users through ingestion; although the clinical significance of this exposure is uncertain (Leonard et al.,
2015). The ‘Beach Bums’ study, conducted by the ECEHH
(http://www.ecehh.org), will use rectal swabs from regular
surfers to investigate gut colonization by AMR bacteria in
this group highly exposed to seawater.
CONCLUSIONS
Current evidence suggests that the burden of infectious
disease from marine bathing is significant at a societal level,
although, with notable exceptions, less so individually.
Priorities for further research include better understanding
of sources, reservoirs and the burden of disease from pathogens in the marine environment. Additional studies are
required to identify appropriate markers for risk at non-point
source beaches. The use of novel, rapid, molecular techniques
can potentially inform rapid interventions to protect the
health of bathers. Nonetheless, despite limitations, practical
advice can be given to bathers based on current evidence to
minimize their risk of illness; the public should be advised
to avoid bathing following heavy rainfall, not ingest seawater,
cover all skin lesions, shower with fresh water before and after
bathing, wear protective equipment if necessary, and be aware
of the additional risks in the presence of impaired immunity
and open wounds. Bathers who become unwell should seek
medical attention, with medical practitioners encouraged to
seek microbiological confirmation of the cause of illness.
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Correspondence should be addressed to:
N. Young
University of Bristol, Bristol, UK
email: nick.young@phe.gov.uk