Microbiological quality in Finnish public swimming pools and whirlpools with special reference to free living amoebae: a risk factor for contact lens wearers?

To assess the possible risk of microbial keratitis associated with swimming or bathing in public pools, the microbiological quality as well as the presence of free living amoebae in 16 halogenated swimming pools and whirlpools, located in Helsinki, Finland, was determined. Five additional whirlpools situated in the ferries cruising from Finland to Sweden were included in the study. Other parameters investigated were the total bacterial count, identification of Pseudomonas aeruginosa and Staphylococcus aureus, measurement of free residual and combined chlorine, potassium permanganate index, urine, pH, and turbidity. Amoebae were detected in 41% of the pool water samples studied. Seven of 11 whirlpools and four of 10 swimming pools were shown to contain amoebae. An Acanthamoeba species was isolated from only one outdoor swimming pool; the other amoebae belonged to the genera Vexillifera, Flabellula, Hartmannella, and Rugipes. Although not a single verified case of Acanthamoeba keratitis has been found in Finland, the findings show that there is a theoretical risk of amoebic and bacterial keratitis associated with swimming or bathing in properly cleaned public pools. Consequently, we do not recommend swimming or bathing with contact lenses.