Relationship between the occurrence of coliphages and E. coli in Danish marine bathing areas

During 2 bathing seasons, 1978 and 1979, water samples were collected with intervals of 2 weeks from 17 marine bathing areas situated on the coast of the island of Fyn. Quantitative examinations for coliphages and fecal coliforms were carried out. Coliphages were present in approximately 50% of the samples. 75% of the positive samples contained less than or equal to 10 coliphages per 100 ml. 6 samples were found with greater than 100 coliphages per 100 ml. A positive correlation between coliphage and fecal coliform concentrations was demonstrated. The ratios of fecal coliforms to coliphages varied only little between individual sampling stations. The mean ratio was 1.9 and 2.0 for the 2 sampling periods. The mean concentration of fecal coliforms was gradually increasing from 2.4/100 ml in May to 7.2/100 ml in September. Conversely the coliphage concentrations were quite uniform during the bathing seasons. As a result of those 2 trends, the fecal coliform/coliphages ratio increased during the seasons from 0.86 to 3.13. Finally, the potential value of coliphages as an indicator of pathogenic microorganisms in marine bathing areas is discussed.