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Pathogens are small disease-causing microbes, including bacteria, viruses, fungi and some parasites. A single liter of ocean water can carry up to 1 billion bacteria and 10 billion viruses.  

The majority of microbes pose little to no health risk, some can be harmful to humans, marine species and ecosystems. No global databases yet exist that could be used to indicate the numbers or trends of pathogens that affect marine organisms. Therefore the Ocean Health Index only assesses pathogens that directly affect humans and uses them as a pressure that impacts three goals: Tourism & Recreation, Livelihoods & Economies and Clean Waters. 

Pathogens that affect humans usually enter the ocean because of poor sanitation practices, runoff of animal waste, and discharge from ships and boats. 

Countries that are poverty-stricken, war-torn or politically unstable are generally more susceptible to pathogenic diseases like typhoid fever, dysentery and cholera because of poor infrastructure, lower standards of sanitation or hygiene, and inadequate maintenance of water supplies (Sedas 2007).

Sources Of Pathogens

How Was It Measured?

Few countries make direct measurements of pathogen contamination in their coastal waters so there is no global database for this variable. Therefore the Ocean Health Index used an indirect estimate of marine pathogen contamination based on the percentage of each country's coastal population that has access to improved sanitation facilities that effectively prevent contact with excreta. Raw data are derived from the latest data available from the World Health Organization and United Nations Children's Fund's Joint Monitoring Programme (WHO/UNICEF's JMP). The reference point is the maximum target that 100% of the population in every country has access to improved sanitation facilities.

The Clean Water goal is unusual because its four components--Pathogen Pollution, Chemical Pollution, Nutrient Pollution and Trash Pollution--indicate both Status and Pressure.  Low levels of those factors produce a high goal score, but high levels produce a low score.  For example, perfectly clean water has no pathogen pollution, so Status for this component is expressed as 1 - the percentage of the population served by adequate sanitary facilities. Status for the other components is similarly expressed.  Input data for calculating Status and Pressure for each component is listed in Table S23 of Halpern et al. 2015.  The overall goal score is the geometric mean of the scores for the four components, which are weighted equally.    

Use of the geometric mean magnifies the importance of a very bad score for any one of the components, matching public perception that very high levels of a single pollutant would make waters seem โ€˜too dirtyโ€™ to enjoy for recreational or aesthetic purposes.

For each country the Status of Pathogens is calculated as % of the coastal population with access to improved sanitary facilities รท 100%.

All pressures are ranked for their differing affects on different goals. For each goal, the effect of each pressure is weighted 'low' (1), 'medium' (2) or 'high' (3). The actual data-derived value of the pressure is then multiplied by the weight assigned to it for that goal. That process is repeated for each pressure-goal combination.  The sum of those values divided by 3 (the (the maximum pressure-goal value) expresses the total affect of pressures on the goal.

Pathogen pollution affects three goals, Tourism & Recreation, Livelihoods & Economies (Tourism component) and Clean Waters.  Its impacts on all of them are high (weight = 3).

What Are The Impacts?

3.5 Million Cases of Cholera Occur Annually


Marine animals can become sick or die when exposed to pathogens. Coral reefs are also particularly susceptible to bacterial infections, which can inhibit their ability to provide a wide range of ecosystem services.

Overuse of antibiotics in humans and livestock has led to the development of strains of antibiotic-resistant pathogens. 

A 2008 study found that 78% of marine animals off the coast of New England had contracted at least one antibiotic-resistant bacterium, and over 50% had contracted two or more antibiotic-resistant bacteria (WHO 2008).


Humans can become ill from bathing in or ingesting contaminated water, or consuming contaminated seafood. The most widespread and harmful pathogenic illness is cholera, caused by Vibrio cholera, which causes severe diarrhea and dehydration and can be fatal if left untreated. V. fulnificus and V. parahaemolyticus are two other species in the cholera family that are commonly found in mangroves, estuaries and marshes. Exposure to these pathogens through raw/undercooked seafood or infection through wounds can cause vomiting, diarrhea, and potentially fatal infections in humans.


Pathogens threaten jobs and income in the seafood, tourism and recreation industries. Fear of contamination lowers consumer confidence and closed beaches reduce attendance. The health costs of pathogenic infections are also great. In Los Angeles and Orange County, California, fecal contamination at beaches causes between 627,800 and 1,479,200 additional gastrointestinal illnesses each year, generating a public health cost of US $21 to $51 million (Given 2006).

What Has Been Done?

In 1999, Royal Caribbean Cruise Lines (RCCL) was convicted of 21 felony counts in six different U.S. courts for dumping oil and hazardous chemicals illegally. The company was required to pay a criminal fine of US $18 milllion, the largest ever to be paid by a cruise line in connection with polluting U.S. waters (U.S. Department of Justice 1999).  In 2004, under pressure from Oceanaโ€™s eleventh-month Stop Cruise Pollution campaign, Royal Caribbean committed to install Advanced Wastewater Purification (AWP) systems on all of its ships. Wastewater processed by AWP technology exceeds all international ship wastewater discharge standards. As of April 2009, nine ships were outfitted with AWP systems, and thirteen more were expected to be outfitted with AWP technology by the end of the year (RCCL 2009). 

Get More Information

United States National Oceanic and Atmospheric Administration (NOAA):ย  Oceans & Human Health Initiative

Research project identifying and investigating which terrestrial pathogens are affecting ocean health.

World Health Organization (WHO)

WHO report on water sanitation addressing exposure and risk of disease.

Woods Hole Center for Oceans & Human Health (WHCOHH)

The WHCOHH addresses the distribution of pathogens in regard to oceanic processes.

Getting a Grip on Cruise Ship Pollution

A review of cruise ship pollutant issues prepared by Ross A. Klein, PhD, for Friends of the Earth. December 1, 2009. 


Beeton, R., Buckley, K., Jones, G., Morgan, D., Reichelt, R., Trewin, D. (Australian State of the Environment Committee). (2006). Australia State of the   Environment. Independent report to the Australian Government Minister for the Environment and Heritage, Department of the Environment and Heritage, Canberra.   1-141.

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