Journal of Hospital Infection (2002) 52: 243±249 doi:10.1053/jhin.2002.1293, available online at http://www.idealibrary.com on An evaluation of the efficacy of Aqualox for microbiological control of industrial cooling tower systems E. L. Prince*, A. V. G. Muiry, W. M. Thomasz, R. J. Stollardx, M. Sampsonx and J. A. Lewis{ *Department of Biological Sciences, University of Central Lancashire, Preston, PR1 2HE, UK; ySterilox Technologies Inc, Yardley, Philadelphia, USA; zCurdmont House, PO Box 5463, Sutton Coldfield, West Midlands, B76 9HN, UK; xSterilox Technologies International Ltd., 85E Milton Park, Abingdon, UK; and {Waterman Environmental Services Ltd, Minworth Industrial Park, Sutton Coldfield, B76 1AH, UK Summary: A comprehensive sampling protocol was employed to evaluate the efficacy of Aqualox, a biocide based on electrochemically activated water, against legionellae and heterotrophic bacteria in two industrial cooling tower systems. Both of the towers in the study remained free from evidence of Legionella spp. con- tamination throughout a five-month evaluation period, despite the previously demonstrated presence of legionellae in one of the test towers, and in two other towers on the same site, at levels well in excess of UK Health and Safety Commission (HSC) Approved Code of Practice and Guidance (ACOP) upper action limits. Levels of heterotrophic bacteria were controlled below 10 4 cfu/mL in both towers throughout most of the trial. Results also provided indirect evidence of significant activity against biofilm bacteria, with biofilm removal beginning almost immediately after commissioning of the Aqualox treatment systems. The results were particularly encouraging as the two towers studied had a long history of poor microbiological control using conventional bromine-based biocide products. Significant differences were observed between laboratory measurements of total viable counts on frequent liquid samples and those obtained from dip slides following HSC recommendations. & 2002 The Hospital Infection Society Keywords: Aqualox; Sterilox; Legionella; cooling towers; mixed oxidants. Introduction Legionnaires' disease, caused by the bacterium Legionella pneumophila, is a severe form of pneu- monia. 1 In several hospital outbreaks, patients are thought to have been infected through exposure to contaminated aerosols generated by cooling towers. 2±5 Legionellae resident within biofilms are a particular problem in cooling tower systems, 6 and can prove difficult to eradicate by conventional means. LeChevalier et al. 7 reported that biofilm bacteria can be up to 3000 times more resistant to standard chlorine disinfectants than unattached cells. Bradford and Baker 8 and Crayton et al. 9 have demonstrated that mixed oxidants, in contrast, exert dramatic activity against biofilms. Aqualox is an aqueous solution of mixed oxidants, generated on-site by electrolysis of a dilute saline solution in a proprietary electrochemical cell, using the same technology as that employed to produce the Sterilox fluid utilized in medical applications. Aqualox generators are supplied with a concentrated Received 2 October 2001; revised manuscript accepted 10 July 2002. Author for correspondence: Dr Mark Sampson, Senior Micro- biologist, Sterilox Technologies International Ltd, 85E Milton Park, Abingdon, Oxon, OX14 4RY, UK. 0195±6701/02/120243  07 $35.00/0 & 2002 The Hospital Infection Society