Bacterial levels in seawater were measured 3 times a week at 4 beaches in Santander, northern Spain. The study lasted from the beginning of July to mid-September 1998.
The findings were reported in the Journal of Epidemiology and Community Health.
A sample of over 2,000 bathers were interviewed during this period, and included all people on the beach living in the same household. Over 1,800 people were contacted again 7 days later to see if they had developed any symptoms.
Predominantly gastrointestinal, skin, and respiratory symptoms were reported by 7.5% of the respondents. Visitors reported more symptoms than residents did.
The water was so polluted, I could not swim properly - all I could do was go through the motions.
Symptoms correlated with total numbers of intestinal bacteria (coliforms) and bacteria found in fecal matter, with gut and skin symptoms associated with coliform numbers.
Levels of coliforms between 2,500 and 10,000 for every 100 ml of seawater, increased the risk of symptoms, with swimmers 10 times as vulnerable as non-swimmers. This level is above the European Union guide standard for microbial contamination.
Almost 40% of water samples exceeded the guide standard for total coliforms.
57% and 38% of samples exceeded the guide standard for fecal coliforms and other fecal bacteria, respectively.