Isolation of mycobacteria from indoor swimming pools in Finland

The presence of mycobacteria in seven indoor pools in Finland was evaluated by multiple culture methods. Replicate samples, with and without inactivat ion of chlorine by sodium thiosulfate, were cultured in two laboratories. L aboratory I used two methods: (A) no decontamination and (B) cetylpyridiniu m chloride (0.005%, 20 min); and Laboratory II two methods: (C) cetylpyridi nium chloride (0.005%, 18 h) and (D) oxalic acid (5%, 15 min). Samples proc essed by methods (A) and (B) were cultured on different egg media of pH 6.3 or 5.8; by method (C) on Middlebrook and Cohn 7H10 (+OADC) agar of pH 5.5; and by method (D) on Middlebrook and Cohn 7H10 agar (+OADC) with cyclohexi mide (500 mu g/ml). Mycobacteria were recovered from five (71%) of seven po ols. Detection of mycobacteria depended on the method used. High isolation rates (36-46% of the samples) were obtained by methods (A), (B) and (D). Co ntamination was a problem only with method (A). Inactivation of chlorine ha d a variable impact on mycobacterial detection. Isolates included M. kansas ii, M. gordonae, M. fortuitum complex, M. sphagni, and M. vaccae, as well a s M. simiae-like and M. chubuense-like organisms. In addition, a group of s lowly growing and a group of rapidly growing isolates with previously unkno wn fatty acid and alcohol composition were isolated. No M. avium was detect ed. Mycobacterial counts were highest in a small pool with high temperature , low pH, and low content of free available chlorine.