Risk of swimming-acquired illnesses in Mamala bay

Swimming, windsurfing, canoeing and other recreational acnvines in polluted waters containing fecal coliform and virus levels similar to those detected on occasion in Mamala Bay have been associated with disease. Low levels, even one virus or protozoan cyst, have the potential to cause disease. Risk estimates can be made for specific microbial pathogens contaminating waterways using dose-response models. These models have been used to evaluate health risks by the Environmental Protection Agency under the Safe Drinking Water Act for the development of proper controls. The potential of acquiring an infection from Enteroviruses, Adenoviruses, Cryptosporidium and Giardia was determined for four beaches where there were monitoring data available. Risk of acquiring a viral or protozoan infection was estimated for swimmers who were exposed for 7 days. Here it was assumed that throughout the year the average numbers of viruses or protozoa represent the best estimate of a daily concentration. The risks for viruses range from a low of 1/1000 at Waikiki Beach to a high of 5/1000 at Queens Surf Beach. The total viral risks at the four beaches were compared to the risk of acquiring a viral infection in general by other routes (for example, contact with someone who is excreting a virus, person to-person contact). Chances of acquiring a viral infection from swimming at these beaches is equivalent or greater than the chance of acquiring an infection from all other sources during the fall and spring, but is 2 to 10 times lower in the summer when virus infections are generally greater in the population. The risks for protozoa range from a low of 2/100,000 at Hanauma Bay to a high of 9/100,000 at Waikiki Beach. In this case, swimming is a greater risk by as much as 4.5 times compared to other means of acquiring the infection. In fact, Center for Disease Control suggest that 60 per cent of all cases of Giardiasis are waterborne. It should be kept in mind that these risks represent infections and not clinical illness. However, those individuals who do become infected can serve as a source for spreading the disease to others.