Ionization Failure Not Due to Resistance

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Abstract
Sir—Rohr et al. [1] report their experience with copper-silver ionization in eradicating Legionella in the hot water plumbing systems of a German university hospital. They report that the percentage of 1-L samples of water from distal sites that were positive for Legionella (the detection limit was 1 cfu/L) were as follows: before installation of the ionization unit, 100%; in year 1 after installation, 55%; in year 2, 76%; in year 3, 78%; and in year 4, 75%. From this data it appears that the copper-silver ionization system installed in this hospital did not effectively control Legionella in the water plumbing system, even in the first year. Although the number of cfu of Legionella detected decreased in the first year, the percentage of samples positive for Legionella remained as high as 55%. Cases of hospital-acquired legionnaires disease correlate directly with percentage of samples that are positive for Legionella [2, 3–4], but not with the number of Legionella organisms detected at each distal site.