(140 to 158 °f) to 80 °c (176 °f) – disinfection range 66 °c (151 °f) – legionella dies within 2 minutes 60 °c (140 °f) – legionella dies within 32 minutes 55 °c (131 °f) – legionella dies within 5 to 6 hours water can be monitored in real-time with sensors. chlorine a very effective chemical treatment is chlorine. for systems with marginal issues, chlorine provides effective results at >0.5 ppm residual in the hot water system. for systems with significant legionella problems, temporary shock chlorination—where levels are raised to higher than 2 ppm for a period of 24 hours or more and then returned to 0.5 ppm—may be effective. hyperchlorination can also be used where the water system is taken out of service and the chlorine residual is raised to 50 ppm or higher at all distal points for 24 hours or more. the system is then flushed and returned to 0.5 ppm chlorine prior to being placed back into service. these high levels of chlorine penetrate biofilm, killing both the legionella bacteria and the host organisms. annual hyperchlorination can be an effective part of a comprehensive legionella preventive action plan. copper-silver ionization industrial-sized copper-silver ionization is recognized by the u.s. environmental protection agency and who for legionella control and prevention. copper and silver ion concentrations must be maintained at optimal levels, taking into account both water flow and overall water usage, to control legionella. the disinfection function within all of a facility's water distribution network occurs within 30 to 45 days. key engineering features such as 10 amps per ion chamber cell and automated variable voltage outputs having no less than 100 vdc are but a few of the required features for proper legionella control and prevention, using a specific, nonreferenced copper-silver system. swimming pool ion generators are not designed for potable water treatment. questions remain whether the silver and copper ion concentrations required for effective control of symbiotic hosts could exceed those allowed under the u.s. safe drinking water act's lead and copper rule. in any case, any facility or public water system using copper-silver for disinfection should monitor its copper and silver ion concentrations to ensure they are within intended levels – both minimum and maximum. further, no current standards for silver in the eu and other regions allow use of this technology. copper-silver ionization is an effective process to control legionella in potable water distribution systems found in health facilities, hotels, nursing homes, and most large buildings. however, it is not intended for cooling towers because of ph levels greater than 8.6, that cause ionic copper to precipitate. furthermore, tolyltriazole, a common additive in cooling water treatment, could bind the copper making it ineffective. ionization became the first such hospital disinfection process to have fulfilled a proposed four-step modality evaluation; by then, it had been adopted by over 100 hospitals. additional studies indicate ionization is superior to thermal eradication. chlorine dioxide chlorine dioxide has been approved by the u.s. environmental protection agency as a primary disinfectant of potable water since 1945. chlorine dioxide does not produce any carcinogenic byproducts like chlorine when used in the purification of drinking water that contains natural organic compounds such as humic and fulvic acids; chlorine tends to form halogenated disinfection byproducts such as trihalomethanes. drinking water containing such disinfection byproducts has been shown to increase the risk of cancer. clo2 works differently from chlorine; its action is one of pure oxidation rather than halogenation, so these halogenated byproducts are not formed. chlorine dioxide is not a restricted heavy metal like copper. it has proven excellent control of legionella in cold and hot water systems and its ability as a biocide is not affected by ph, or any water corrosion inhibitors such as silica or phosphate. however, it is 'quenched' by metal oxides, especially manganese and iron. metal oxide concentrations above 0.5 mg/l may inhibit its activity. monochloramine is an alternative. like chlorine and chlorine dioxide, monochloramine is approved by the environmental protection agency as a primary potable water disinfectant. environmental protection agency registration requires a biocide label which lists toxicity and other data required for all registered biocides. if the product is being sold as a biocide, then the manufacturer is legally required to supply a biocide label, and the purchaser is legally required to apply the biocide per the biocide label. when first applied to a system, chlorine dioxide can be added at disinfection levels of 2 ppm for 6 hours to clean up a system. this will not remove all biofilm, but will effectively remediate the system of legionella. moist heat sterilization moist heat sterilization (superheating to 140 °f (60 °c) and flushing) is a nonchemical treatment that typically must be repeated every 3–5 weeks. ultraviolet ultraviolet light, in the range of 200 to 300 nm, can inactivate legionella. according to a review by the us epa, three-log (99.9%) inactivation can be achieved with a dose of less than 7 mj/cm2. biomonitoring a legionella-specific aptamer has been discovered and in 2022 was developed into an assay for detecting to a limit of 104.3 cells/ml with no processing steps. european standards several european countries established the european working group for legionella infections to share knowledge and experience about monitoring potential sources of legionella. the working group has published guidelines about the actions to be taken to limit the number of colony-forming units (that is, live bacteria that are able to multiply) of legionella per litre: legionella bacteria cfu/litreaction required (35 samples per facility are required, including 20 water and 10 swabs) 1000 or lesssystem under control more than 1000up to 10,000review program operation: the count should be confirmed by immediate resampling. if a similar count is found again, a review of the control measures and risk assessment should be carried out to identify any remedial actions. more than 10,000implement corrective action: the system should immediately be resampled. it should then be "shot dosed" with an appropriate biocide, as a precaution. the risk assessment and control measures should be reviewed to identify remedial actions. (150+ cfu/ml in healthcare facilities or nursing homes require immediate action.) monitoring guidelines are stated in approved code of practice l8 in the uk. these are not mandatory, but are widely regarded as so. an employer or property owner must follow an approved code of practice, or achieve the same result. failure to show monitoring records to at least this standard has resulted in several high-profile prosecutions, e.g. nalco + bulmers – neither could prove a sufficient scheme to be in place while investigating an outbreak, therefore both were fined about £300,000gbp. important case law in this area is r v trustees of the science museum 3 all er 853, (1993) 1 wlr 1171 employers and those responsible for premises within the uk are required under control of substances hazardous to health to undertake an assessment of the risks arising from legionella. this risk assessment may be very simple for low risk premises, however for larger or higher risk properties may include a narrative of the site, asset register, simplified schematic drawings, recommendations on compliance, and a proposed monitoring scheme. the l8 approved code of practice recommends that the risk assessment should be reviewed at least every 2 years and whenever a reason exists to suspect it is no longer valid, such as water systems have been amended or modified, or if the use of the water system has changed, or if there is reason to suspect that legionella control measures are no longer working. weaponization legionella could be used as a weapon, and indeed genetic modification of l. pneumophila has been shown where the mortality rate in infected animals can be increased to nearly 100%. a former soviet bioengineer, sergei popov, stated in 2000 that his team experimented with genetically enhanced bioweapons, including legionella. popov worked as a lead researcher at the vector institute from 1976 to 1986, then at obolensk until 1992, when he defected to the west. he later divulged much of the soviet biological weapons program and settled in the united states.