Many studies show
that respiratory and intestinal diseases and infections among bathers rise steadily
in step with the amount of sewage pollution in the water. They demonstrate,
too, that bathers are at risk even in lightly contaminated waters that meet
the pollution standards laid down by the European Union and the US Environmental
Protection Agency.
A recent WHO report has estimated that one in every 20 bathers in "acceptable waters", will become ill after venturing just once into the sea. The GESAMP/WHO study -- based on global estimates of the number of tourists who bathe, and WHO estimates of the relative risks at various levels of contamination -- estimates that bathing in polluted seas causes some 250 million cases of gastroenteritis and upper respiratory disease every year. Some of these people will be disabled over the longer term.
The global impact can be measured by adding up the total years of healthy life that are lost through disease, disability and death using a new measurement -- the Disability Adjusted Life Year (DALY) -- developed by WHO and the World Bank. When this is done, the world-wide burden of disease incurred by bathing in the sea adds up to some 400,000 DALYs, comparable to the global impacts of diphtheria and leprosy.
It is estimated to cost society, worldwide, about US $1.6 billion a year.
The toll from consuming contaminated shellfish is even greater. One study suggests that seafood is involved in 11 percent of all the outbreaks of disease carried in food in the United States, 20 percent of them in Australia, and over 70 percent in Japan, which has a particularly strong tradition of eating raw fish and shellfish.
Pathogenic bacteria can survive in the sea for days and weeks; viruses can survive in the water -- or in fish and shellfish -- for months. The particularly virulent infectious hepatitis virus -- which has caused many outbreaks of the disease associated with eating shellfish -- can remain viable in the sea for over a year. Shellfish, like oysters, mussels, clams and cockles, feed by filtering huge amounts of seawater -- and can concentrate viruses and bacteria a hundredfold from the water in which they live.
A series of studies has found viruses in about a fifth of the shellfish taken from waters that meet US bacteriological standards for growing and harvesting them. There is strong evidence that fresh shellfish -- on sale for food -- frequently contain enough viruses to make many of those who eat them ill. They are often eaten raw, or after only a light steaming which is not enough to kill most of the viruses or bacteria.
One US study suggested that one in every hundred people eating relatively lightly contaminated raw shellfish will be infected with a moderately serious intestinal virus disease; the risk rises to up to 50 in a 100 if the virus is highly infectious. Other studies in both the United States and the United Kingdom suggest that a quarter of those who are taken to hospital suffering from infectious hepatitis -- a disease that can confine sufferers to bed for two to three months -- have caught it from eating raw or lightly steamed shellfish.
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Some eight billion meals of shellfish are thought to be eaten world-wide each
year. The GESAMP/WHO study estimates that eating sewage-contaminated shellfish
raw causes some 2.5 million cases of infectious hepatitis each year. Some 25,000
of the victims die, and another 25,000 suffer long-term disability from liver
damage. The global burden on human health equals some 3.2 million DALYs a year
- comparable to the worldwide impact of all upper respiratory infections and
intestinal worm diseases - and costs world society some US$
10 billion annually.
-- GESAMP70:6
Table of health costs of contaminated marine water and shellfish (Document)
Impact of Marine Environmental Pollution on Human Health (Document)