For copper-silver ionization systems, what are the calculations to convert ionization cell current (assume 100mA) to ppm for a given water flow rate please? Assume pH of 7 and potable water.

         The generating capacity is flow dependent.  At 6 gallons per minute, the system will generate 0.5ppm (mg/L) per amp.  If using 70:30 electrodes: 7 amps at 6 gpm = 3.5 ppm copper or 0.5 ppm per amp.  At 100mA output and a 6 gpm flow rate. 0.05 ppm of copper would be generated. 

Has Legionnaires’ disease been reported from the workplace?  I need information about that.

         Many incidents of Legionnaires' disease in the workplace have been reported.  We reported two cases at a plastic injection mold plant.  P Muraca, JE Stout, VL Yu, YC Yee.  Legionnaires' disease in the work environment: implications for environmental health. Am Ind Hyg Assoc J 49:584 590, 1988. Another reference is Fry et al, Legionnaires' disease outbreak in an automobile engine manufacturing plant.  J Infect Dis 2003; 187: 1015-1018.

A client of ours is installing an evaporative sea water cooling tower.  Can Legionella survive in sea water cooling tower conditions?  Are there any published papers covering sea water applications?

        There is some anecdotal evidence that water samples collected from sea water cooling towers were negative for Legionella.  Survival of Legionella in marine environments is limited by both salinity and warmer temperature. 

We have found Legionella in a sink and floor drain of a building on campus, some of the results have come back as "present, but below quantifible levels", and others in the 500 cells/swipe area.  I really don't know what these numbers mean.  One of the occupants has been diagnosed with a"Legionella-like disease", who believes that when the plumbers worked on the system the previous week "caused her disease".  This doesn't make any sense to me, however.  Does the 500 number sound high, normal, etc.?  Does this mode of infection make any sense?

    Given that the mode of transmission of Legionella bacteria is either via exposure to intense aerosol or aspiration (after drinking contaminated water or after direct instillation into the upper airway), it is not common to culture the drain of a sink or a floor drain.  A more appropriate location is the sink faucet or the water in the hot water distribution system.  We already have an answer on the web site to your question regarding culture results and quantity vs. extent of colonization on the website.  Quantitation is not a useful parameter to gauge risk. 

         Regarding the individual with the "Legionella-like disease", our first question is whether a diagnostic test for Legionnaires' disease was performed (Legionella urine antigen test or respiratory culture) and whether this test was positive.  If a diagnosis of Legionnaires' disease cannot be confirmed, then you need not perform any environmental investigation.

Does the condensate drain on a conventional domestic air conditioner provide a risk of catching the Legionella disease. It has been suggested by my local authority that the reason for connecting the condensate drain to sewer is to reduce the risk of contracting Legionella.

         We are not aware of any cases of Legionnaires' disease acquired from a condensate pan or drain.  There would be little opportunity for significant exposure.  One benefit of connecting the drain to the sewer is that there might be no need to chemically treat the condensate pan.  These pans can often be the source of foul smelling bacteria and molds.

I am a Senior Director of Engineering for retirement communities.  We had a problem in the first two buildings there.  Scaling had built up on the copper pipes as the water softening system was not put into operations until 6 months after opening.  We suspected that the scaling encouraged the harboring of Legionella bacteria.

1.     Is it a reasonable assumption that scaling on pipe assists the bacteria in harboring and subsequently colonizing?

2.     As galvanized pipe naturally encourages scale buildup, is galvanized pipe a poor selection for domestic water systems?

3.     Does the size of the pipe make a difference?

        1. Scale does provide a surface area for biofilm accumulation, but it is not necessarily a critical factor.  We have demonstrated rapid colonization of a newly constructed building (Legionnaires' disease in a newly constructed long-term care facility.  J. Am. Geriatric Society. 48: 1589-1592, 2000).

        2. We believe that galvanized pipe is not the best choice for water distribution systems.  One of our newer facilities was constructed with extensive use of galvanized pipe in both the cold and hot water systems.  They are now having to replace large sections of pipe due to corrosion.  New copper piping is inhibitory to Legionella.  We learned this since our early model water systems were constructed of copper; it was difficult to keep Legionella alive in this system. 

        3. We do not think pipe size is a factor, but we have never tested this hypothesis.  We have found that higher flow causes more Legionella to be deposited on the pipe surface due to mass transfer. 

As part of a renovation/new building plan, an executive would like to put a water wall in the entrance of the hospital.  Five glass panels will be put up and water will be recirculated for continuous flow.  Do you see any potential problems with this presentation?  In addition, there will be no barriers to prevent people from putting their hands in the water and creating a diversion of the water flow. 

    We discourage the installation of decorative fountains in hospitals.  However, the water wall in the photo that you provided, aerosolization is unlikely, so the risk would be very low.  The water fountains can be treated with disinfectants such as chlorine or bromine.

I am involved with a volunteer group who wish to place a small bubble fountain in an external patient "sensory garden" at a local hospital.  The fountain will not be connected directly to any water supply and will recuirculate the water it uses. Some members of hospital maintenance staff have cited risk from Legionella as a reason to oppose the fountain. Would you consider the risk significant given that the fountain is outside and not connected directly to the potable water supply?

    We believe that the risk for Legionella infection in your situation is small. And, many of the outbreaks linked to fountains may have been incorrect; nevertheless, given the undue publicity of Legionnaires' disease and fountains, we believe it would be prudent to avoid this issue altogether. So, for hospitals, we discourage the placement of fountains. The fact that the water is recirculating rather than coming from the potable water supply does not mean that Legionella will be absent or even have a lower likelihood of being colonized with Legionella.

I am a drinking water engineer at a Department of Health.  The Health Department by statute is a member of the state Plumbing Board. Recently, the Plumbing Code was updated and due to the Health Department's efforts to reduce the risk of Legionella, all water tanks must now be maintained 140 degrees F.  To prevent scalding, mixing valves are required, so that at the tap, consumers don't receive water hotter than 120 degrees F. at any tap/shower.

We have been approached by the manufacturers and lawyers of tankless heaters for a waiver.  Their argument is that tankless heaters don't have a reservoir where Legionella could amplify, their product is simply a flash heater of the cold water line. As we don't treat cold water per se for Legionella, I think their argument holds merit, but I deferred to our nurse epidemiologist.  She provided me with the ASHRAE standards which don't exactly address this situation, but do quote 140 degrees for health care facilities hot water storage and quoted the Legionella growth temperature range of 77-108 degrees F.

Would you be able to comment on tankless heaters and the efficacy of holding them to a standard promulgated specifically to reduce Legionella risk?

        We once thought, as you suggested, that elimination of the large volume hot water heater would significantly reduce Legionella colonization in the hot water system.  In a survey of 15 hospitals in western Pennsylvania, in 2 hospitals with instantaneous steam heating systems (tankless heaters) no Legionella was isolated from these hospitals.  We then replaced the 1000+ gallon hot water tanks in one of our VA hospitals with instantaneous heaters in an effort to decrease Legionella colonization.  These heaters flash heated the cold water to 190^o and then blended the water back down to the pre-set temperature (which was 140^oF). Disappointingly, this installation had virtually no effect on the downstream colonization of fixtures.  We now understand that the entire network of pipes is coated with a slime layer (biofilm) within which Legionella resided.  The bulk of the Legionella colonization of the water system was downstream of the hot water tanks!  This is why active disinfection throughout the system is required to control Legionella bacteria in warm water systems. So, if the temperature of the blended water as it exits from the tankless heater is 140^oF, then that should satisfy the Health Department’s objective.

I was interested to read that air conditioning systems are not a source.

Air conditioning systems and cooling towers can harbor and support the abundant growth of Legionella. We, however, do not believe the source of Legionnaire's disease is by means of inhalation of mists from air conditioning systems. Instead, we believe aspiration of Legionella in drinking water containing the bacterium is the major source.  Nonetheless, cooling systems are disinfected to try to prevent the growth of Legionella in this equipment, both to prevent a possible health issue and to decrease biofouling of equipment.

Is ozone used at all to disinfect contaminated (or suspected) areas.

Ozone can be used to disinfect for Legionella, however ozone leaves no residual for long-term control of Legionella in distribution systems.  Ozone has been evaluated in a water distribution system, but results were inconclusive.  To see an overall evaluation, please see Lin JAWWA 1998 in Publications. 

You may want to look at the following web page which contains other commonly used biocides in potable and cooling tower waters: http://www. Legionella.org/biocides_research1.htm.
 

I am a heating and air conditioning service technician.  Often the condensation drain lines on air conditioning equipment become clogged with a reddish sludge.  It is necessary to clear the drain with suction to prevent blowing the material back into the drain pan.  In the past I have connected clean pipe to the drain line and sucked the obstruction loose careful not to get a mouthful of dirty water.  After reading the information on your site and another site, this method is obviously wrong.  What kind of risk have I put myself in. and if there is a risk why don't I know more about it.

The risk to you is obviously small because you never have gotten sick.  But the sludge may contain germs or toxins that may enter your mouth accidentally. If they got into your lung (which is possible if you are a smoker) you might contract pneumonia. And, if they got into your stomach, you could get diarrhea.  Except for convenience, there seems no advantage to using your mouth for suctioning. A vacuum apparatus would be safer (but probably less convenient). By the way, what method do you use for unclogging sewage lines?

Is there a specific technology (e.g., in-line UV light unit) that might be appropriate to use with a hospital ice machine to decrease the risk of Legionella contamination of the unit/ice?  We are contemplating purchase of new machines for selected units in the hospital. 

There are numerous point-of-use (POU) treatment technologies that are commercially available.  These technologies typically do not provide a disinfecting residual and include techniques such as UV and filtration.  We have not tested any of these technologies in our VA lab so we cannot provide a recommendation on the "best" one.

There have been recommendations to use simple shock chlorination of the

ice- machine to disinfect.  Go to www.cdc.gov and see MMWR, Vol. 52 (RR10):1-42 Guidelines for Environmental Infection in Health-Care Facilities. You may also wish to talk to your ice-machine vendor about the pre-packaged disinfecting systems, although we have not experience of the validity of the claims of these vendors.

Remember POU technologies only disinfect where they are installed, so without proper maintenance you can still have contamination downstream from the point of disinfection (i.e. in the ice-machine).  You may want to shock-disinfect the machine immediately after installation to help insure the parts down-stream from any POU system are Legionella free, the POU system will help prevent Legionella from reaching the ice-machine and colonizing it.

When water samples are positive for Legionella, is it common or rare to find more than one species present?  Does the presence of one species necessarily indicate others are present, but perhaps not detectable by the lab methods in use? 

It is not unusual to find multiple Legionella species and serogroups in a water system.  There is no data to indicate that the presence of one species correlates or predicts the presence of another species.  Legionella anisa is a common colonizer of water distribution systems.  However, we believe that this species is unlikely to be a pathogen. 

I work in a power plant and we use river water in our cooing system.  I have to enter a vessel where this cooling tower water has passed through.  The river water is treated with sodium hypochlorite and there will not be any vaporizing of the water while individuals are in the vessel.  Should I be concerned with Legionella?

        Since the water will neither be aerosolized nor drunk, the risk should be minimal or non-existent.

If I sample water, how long does it take for results to be available?

        For water samples for Legionella, the results can be available within 5-7 days after the sample has been processed. 

I have a contractor working in a cooling tower known to be infected with Legionella.  What special personal protective equipment do they need to work in that area?  They are wearing tyvex suits, rubber boots, rubber gloves, and a half mask respirator.  Is there any chance they might need a full face respirator due to the mucous membranes in the eyes?

        A P95 half face mask respirator is sufficient to prevent inhalation of Legionella that may be in an aerosol from the tower water.  Legionnaires’ disease is not transmitted via mucous membrane exposure. The rest of the equipment that you mention will protect them from the chemicals commonly used to treat cooling towers.

I have a few questions regarding a facility using chlorine dioxide (ClO₂).  Our infection control group has changed the rooms that are cultured for Legionella to reflect more of the high risk areas, ICU, Heart transplant wards, HIV, etc.  The first round of testing revealed a few positives in these areas. All the counts were very low, only 0.2 to 1.3 cfu/ml.  Swabs taken from these locations were negative.  We claimed that these low numbers certainly reduced risk; however, the physicians wanted to reach zero colonization all the time.  We believe that it is impossible to reach zero.   

        You are correct.  Unfortunately, this is a major flaw for the CDC guidelines for transplant units, which does specify a zero cfu limit.  It is nearly impossible to achieve zero colonization all the time.  Quantitation of cfu/ml is not an accurate indicator for disease, but proportion of sites yielding Legionella is.   

References:

Risk of nosocomial Legionnaires’ disease is better predicted by the proportion of water system sites testing positive for Legionella than by the concentration of Legionella bacteria.  Kool JL, et al. Infect Control Hosp Epid 1999; 20:797-05.

         No correlation between quantitative counts and Legionella cases.  There was a correlation between site positivity (>30%) and cases (Best et al. Lancet 1983; 307-310.)

         No correlation between quantitative counts and Legionella cases (Kohler JR et al. J Hosp Infect 1999; 41:301-311). 

         In our recent experience, no hospital-acquired cases of Legionnaires’ disease were diagnosed at 2 hospitals during our evaluation of Cl0₂ despite the persistence of Legionella pneumophila in the water system.  However, it took many months to significantly reduce the level of Legionella in the system; the percent positivity rate was < 30%.   Moreover, it took many months of chlorine dioxide disinfection to significantly reduce the level of Legionella in the system of both hospitals (Sidari JAWWA 2004).

2.   The question was raised about L. pneumophila building up immunity to low concentrations of C1O2, around 0.8 ppm in hot water.

        I am not aware of any literature demonstrating resistance to 0.8 ppm chlorine dioxide – either Legionella or other bacteria.  You state that the level of chlorine dioxide in the hot water is around 0.8 ppm.  Is that correct?  We have never seen that level in hot water.

3.    Aerators on sinks, should they keep them or get rid of them 

        We would remove them from patient care areas.  We have found aerators and laminar flow devices harbor higher concentrations of bacteria in general.  Removal of aerators or laminar flow devices may necessitate adjustment of water flow to avoid splashing.

I am on the Council in East North Hamptonshire.  I've been asked to provide an update on the subject of Legionella Risk and have visited your web site. I'm following up on the last question, especially the statement that "Air conditioners are not a source for Legionnaires' disease". Preliminary investigations into the recent Barrow in Furness case contradict this. Public Health officials now believe there was a serious flaw in an air conditioning plant thought to be at the centre of the outbreak. These health officials believe that for nearly a month, the air vent had been emitting steam containing bacterium into the alleyway. As you can see, I am now confused!! Can you shed some light on the research that confirms the statement that "Air conditioners are not a source for Legionnaires' disease", or is there a possibility of "language confusion".

        Please download our article in Lancet Infectious Diseases June 2002 for the evidence which is considerable.

        The first case of the elderly individual in this outbreak is an important clue. We were informed that he was never near the air conditioner in question.  And, the public health authorities never even mentioned that the drinking water in the nursing home should be tested. The first place US CDC would have looked would not be the air conditioning, but the drinking water.  In fact, there is not even a single credible case of Legionnaires’ disease clearly linked to an air conditioner in the scientific literature.

Our recommendations

1.    Ask investigative team about culturing the drinking water in large buildings to which the CONFIRMED cases were exposed .

2.    Download the 2 articles on the home page of ww.Legionella.org : the

        ACHD Guidelines and the State of Maryland Guidelines.

        Click onto Publications on www.Legionella.org .  Download the articles

dealing with Environmental Source of Legionella. You will see at once, why Legionella experts across the world (but not in UK) are concerned about the investigation. The source most commonly implicated is not even being mentioned! Dr Bhopal is quoted as saying they do not have to look at patient homes because that never happens. He ignores numerous studies that show that patients indeed can contract Legionella from their homes! (Stout JE, New Engl J Med 1992; Stout JAMA 1987; Pedro-Botet L, Eur J Clin Microbiol Infect Dis 2002. All 3 of these publications can be downloaded from this website).

I take it you aware of what's happening in the UK at the moment - the huge outbreak of Legionnaires.  They say now they think they have found the source - an air conditioning unit - but your research suggests that wouldn't have caused a threat...

    The Stafford outbreak and the BBC outbreak many years ago were attributed to a cooling and air conditioner, respectively by the British Communicable Disease Surveillance Centre.  New data since then suggests that both probably originated from drinking water.

        In the Cumbria outbreak, the first patient was in a rehabilitation facility, I believe.  In numerous scientific publications, patients in rehabilitation facilities who contracted Legionnaires’ disease were found to be infected through the drinking water. Thus, it would be eminently reasonable (and required by US Centers for Disease Control) to culture the drinking water of the facility. Was this logical measure done? Did the first patient have exposure to the air conditioner?

Is it possible to contract Legionnaires’ disease via a compressed air system? We don’t humidify the air but since we use it as oxygen (for breathing connected to mask, etc.), the humidity is at about 85% RH at about 22 degrees celsius. When the air is distributed some water can appear on the way to the consumers. This water is condensate when the pipes gets cold. So what, I wonder is, is it possible to get a growth of Legionella bacteria within the condensed water that originally comes from air humidification? Or do you have to add water as in potable water (town’s water) to get Legionella bacteria? I hope that you can understand my question, if not please let me know so I can specify myself.

    It would be extremely unusual to find Legionella in a compressed air system. In addition, the temperature of such systems are not in the optimal growth range for Legionella.

How is Legionella contracted from spas/hot tubs and what actions ensure that this never happens?  We deal in portable spas and there has been an article in the national paper recently stating that a person has died through infection from a spa.

        Problems occur when biocides are not used or they are used at ineffective concentrations.  The American Society of Heating, Refrigeration Air-conditioning Engineers (ASHRAE) has a section on spas and hot tubs in their publication "Minimizing the Risk of Legionellosis in Building Water Systems".  You can get a

copy from ASHRAE or from the Baltimore Aircoil web site www.baltimoreaircoil .com.

        Legionella must be in contact with the active biocide (chlorine, bromine, etc.) for a sufficient amount of time and at a concentration of the biocide that is active against Legionella.  Maintain the biocide concentration at the recommended level, monitor your biocide levels and keep the system clean. 

Part of our job is to analyze fire protection water supplies.  One of our nemesis is Microbiologically Influence Corrosion.  When looking for a lab to test for MIC, I received  information from one of the testing laboratories who indicated where there is MIC, Legionella bacteria probably will also exist.  Is this true?  If so, are there documented cases? My interest is more in the Fire Protection systems where people are flowing water to test the same. 

        We do not know of any documented cases linking MIC to Legionnaires' disease.  The major mode of transmission of Legionella is through aspiration. This would require a susceptible human to ingest water containing a concentration of Legionella bacteria.  Since consumption of water from fire protection systems is unlikely and assuming your employees are generally in good health, the risk for Legionnaires’ disease is minimal.

What is the upper limit of Legionella for water distribution systems?  

         In contrast to the situation for cooling towers, there is solid scientific data available for interpretation of culture results from hospital water distribution systems.  Risk assessment should not be based on the concentration of Legionella recovered from a given water outlet; quantitation (CFU/ml) does not correlate with incidence of disease (CDC, Infection Control and Hospital Epidemiology 1999, Kohler, Journal of Hospital Infection 1999, Pittsburgh Special Pathogens Laboratory [Best] Lancet 1983).  On the other hand, risk for Legionella infections increase as the extent of colonization with L. pneumophila increases (i.e., a high percentage of water outlets yield Legionella).  In two studies, Legionnaires’ disease did not occur unless the percentage of water outlets reached 30% or greater (Best Lancet 83, Stout, in press). 

       Complete elimination of Legionella from a hospital water system is not necessary to eliminate cases of Legionnaires’ disease in the hospital (Pittsburgh Special Pathogens Lab [Stout], Infection Control and Hospital Epidemiology, 1998). 

Can Legionella survive in chlorinated water? 

        Legionella has been isolated from chlorine treated water.  The levels of Legionella that elude the water treatment process are essentially undetectable.  When this water travels through the system and loses much of the chlorine residual, either from retention time or warm temperatures in water distribution systems, Legionella can then be cultured.  The colonization rate for large buildings is 20-70%, depending on the geographic region. Residential water systems can also harbor Legionella.

It is very interesting to learn from The Lancet Infectious Disease, June 2003 article that virtually all outbreaks have been linked to potable water, and that showering is not a mode of transmission (except perhaps for high risk patients?). 

          Showering is allowed even for high-risk patients. Highly-immunosuppressed patients and COPD (emphysema) patients should drink bottled water or boiled water that has been cooled, but this is optional. If the percent of distal water sites is < 30%, we do not prohibit showering or drinking water for most patients even if Legionella is present in the water.  See our reply to a question about showering in the FAQ from physicians.

We have emergency shower/eyewash combination units in our plant. The units are not used that much. I have heard that the Legionella thrive in cooler water. Is this true and what measures can we take to combat the problem?  The emergency shower/eyewash units are fed from the general potable water supply but are deadlegs as far as general system flow patterns.

        It is possible that Legionella might be in these units, but the risk is negligible, and no infections have even been reported to occur from use of these units.  No guidelines have ever been issued for such units and are probably unnecessary. 

 Emergency showers on water and waste water sites - used for possible chemical splashes etc. Some of these showers have a heated tank. Should these fall under the testing regime for Legionella?

        The major mode of transmission of Legionella is aspiration (so drinking the water is necessary), although intense aerosolization might transmit the organism. In the emergency showers that you describe, the risk would be so low as to not warrant any preventive measure.

Should a water distribution system harboring Legionella anisa be disinfected?

       The majority (>90%) of cases of Legionnaires' disease reported in the U.S. are caused by Legionella pneumophila.  L. anisa is frequently isolated from environmental specimens but almost never causes disease.  L. anisa is generally nonpathogenic and disinfection is not necessarily indicated for this particular species (Yu VL, J Infect Chemother 2004).

I´m a medical student at Karolinska Institute in Sweden currently involved in a project about prevention of legionnaires disease, and I have found your website to be a valuable resource.  I´m writing about the use of free radicals in the elimination of legionella in water systems.  Is this something you are planning on evaluating?  The technique is very interesting and has been proven very efficient on the elimination of Legionella species - among others - in water systems.

        We are assuming you are speaking of the free radicals of oxygen obtained by disinfecting with ozone or hydrogen peroxide.  We have not investigated hydrogen peroxide in our laboratory. The Yamagiwa et al article presents a view of hydrogen peroxide (Yamagiwa K, et al. (2001) Disinfection Kinetics of Legionlla pneumophila by Hydrogen Peroxide.  Journal of Chemical Engineering of Japan. 34(8),1074-1077).  Hydrogen peroxide is slightly more stable than ozone, but maintenance of a sufficient residual in large drinking water systems may still be difficult.  Additionally, we are not sure in the U.S. if hydrogen peroxide could be legally used as a drinking water disinfectant.  If hydrogen peroxide is effective it may be most useful in applications such as spas and whirlpools.  There have been numerous other studies of ozone and we have a listing on www.legionella.org under Research - Legionella Control which compares the recommended concentration with other oxidizing biocides.  Ozone was effective in our model plumbing system (Muraca Appl Environ Microbiol 1987 – see Publications).  One note on ozone, it is very reactive and as such does not produce a residual to carry disinfection effects into a distribution system.  This can be a problem for piping systems which have an established biofilm harboring Legionella far from the point of ozone application.

I work for a building management company which involves controlling domestic hot water tanks, I would like to know what the official minimum storage temperatures are and the length of time they have to be at that temperature. I am under the impression that it is a minimum temperature of 60^oc for at least 1 hour in any 24 hours (therefore the temperature can be dropped for the remaining 23 hours) can you tell me if this is correct. 

    The temperature should remain stable at about 140^oF at the tank.  It would not be wise to only hold this temperature for only one hour and then reduce it.

       Please obtain a copy of the American Society of Heating, Air Conditioning and Refrigeration Engineers (ASHRAE) guide to "Minimizing the Risk of Legionella in Building Water Systems".  This document has a section regarding hot water storage temperature. You can also download a copy from the Baltimore Aircoil web site (www.baltimoreaircoil.com).

    The "official" minimum storage temperatures and durations may vary from country to country and even state to state depending on local guidelines.  As a general source you may want to request guidelines from the following organizations:

       In the US:  http://www.ashrae.org

       In the UK:  http://www.bsria.co.uk/

         If you are interested in Legionella disinfection specific information try the following: http://www.legionella.org/biocides_research1.htm, the table on our website recommends that for potable water systems, heating and flushing can disinfect Legionella.

       Your suggestion of maintaining a water temp greater than 60^oC in the tank for 1 hour may kill Legionella in the tank; however, regrowth of Legionella is likely to occur in the hot water distribution system where temperatures could drop to less than 50^oC depending on use.  Ideally for Legionella disinfection you would want to maintain a high temperature throughout the distribution system (hence flushing).

    Whatever heating regime you try, monitoring of distal sites and the how water tank is necessary to document the effectiveness of disinfection specific to your system and temperature set points.

We have had a copper-silver ionization system on our hot water system for more than a year now.  No cases of hospital-acquired Legionnaires’ disease have occurred since installation, but the copper and silver ion levels are sometimes less than the recommended range by the manufacturer (copper 0.2-0.8 ppm; silver at 0.02-0.08 ppm (20-80 ppb).  Is this cause for alarm or justification to perform additional disinfection like a superheat and flush?

       Our experience indicates that ion levels slightly below the manufacturer’s recommended levels are still effective in systems that have been operational for awhile.  For example, we have had copper levels in the range of 0.1-0.2 ppm and silver at 0.01-0.02 ppm (10-20 ppb).  Our environmental cultures remain well below our threshold of 30% positivity (0-10% most of the time).  I would request either cleaning of the electrodes or adjustments in amperage if the level of copper is at or below 0.1 ppm copper or 0.01 (10 ppb) silver.

       We would not recommend that a decision to perform a superheat and flush be based on ion levels.  This procedure is labor intensive and should be performed in response to either detection of a hospital-acquired case of Legionnaires’ disease or an increase in colonization of the system to 30% or above. 

Questions about non-potable water sources

What is the acceptable upper limit of Legionella in cooling towers?

         We are skeptical that cooling towers are a major source for disseminating Legionella and we predict that many community outbreaks linked to cooling towers will ultimately be shown to be from drinking water.  This is based on the fact that all hospital outbreaks originally linked to cooling towers years ago are now known to have emanated from the hospital drinking water.  For more details, download the following articles from our Publication section (Muder, Arch Int Med 86, Yu Am J Med 93, Sabria Lancet Infect Dis 2002).

         Nevertheless, because of concern about litigation involving Legionnaires’ disease, we receive numerous inquiries about cooling tower maintenance.  Moreover, many water treatment specialists use the service of our Special Pathogens Laboratory for cultures of Legionella in cooling towers. 

         Neither the Centers for Disease Control (CDC) and Prevention nor the Environmental Protection Agency specify a minimum contaminant level for Legionella for cooling towers.  Outbreak investigations have documented both low (<100 Colony Forming Units /mL) and high (>1000 CFU/mL) levels of Legionella in water samples from cooling towers. There are no scientifically based guidelines for establishing risk criteria for Legionella recovery from cooling towers.  Although guidelines have been suggested from a few groups, the data used to establish the relationship of the action levels to disease risk is very limited.  Therefore these guidelines are overly strict (recommending remediation at lower levels) and should be interpreted with caution.

         Links to various websites with guidance documents that suggest levels and interpretation are available on our website by clicking onto “Research” and then “Other Information”. The ASHRAE guidelines 12-2000 is available as a free download from the Baltimore Air Coil website www.baltimoreaircoil.com.

Are chlorine and other oxidizing biocides the only recommended treatment for cooling towers?

Click onto “Research” on the Home Page to see a table of biocides that we and others have found to be effective.  This table was published as part of the American Society of Hospital Engineers technical document on Legionella. 

       There are effective non-oxidizing biocides.  The ASHRAE guideline (available at www.baltimoreaircoil.com) does not recommend a specific biocide, but does recommend that you consult with a water treatment specialist. 

If Legionella is found in decorative fountains, is remediation needed?

       We would discourage the installation of decorative fountains in hospitals.

       For buildings that do not have persons at risk for pneumonia, the water fountains can be treated with disinfectants such as chlorine or bromide. Ultraviolet light may also be effective.  Matt Freije (www.hcinfo.com) recommends draining and cleaning decorative fountains at least twice a year – or more often if slime or dirt is visible. Surfaces can be scrubbed with a disinfecting solution (1 part chlorine to 20 parts water may be appropriate).  Consult a water treatment service for advice.  

I am a journalist working for Norwegian TV.  In the city of Stavanger in Norway, there has recently been several cases of legionella, and investigations conclude that cooling towers most probably are the sources of this outbreak. On your webpage you write that "Cooling towers have long been thought to be a major source for Legionella, but new data suggest that this is an overemphasized mode of transmission". Do you have any numbers or data on how many times i.e. the last outbreaks have been caused by cooling towers?

       Public health authorities downplay the significance of Legionella infections because most originate from drinking water. It is easier to target a cooling tower and harder to discuss with the general public the implications of Legionella in the drinking water.  Note that the investigators said "probably".  All you have to do is to ask the investigators "Did you culture the homes of the patients and their workplaces for legionella". If they refuse to answer, you will have learned something.

       See our recent article Sabria Lancet Infectious Diseases, 2002 on our Home Page.

There are a lot of people who would like to believe that cooling towers are not sources for Legionella infection. I'm sure ASHRAE would love to prove that and let the HVAC design engineers off the hook. On the other hand if it's in the drinking water, why did others in the Wadsworth VA Hospital area, a heavily populated area not come down with Legionnaires’ disease? The Melbourne aquarium was traced to the cooling towers according too Australian public health authorities.   If it's in the drinking water, why have not the people who control the city water, which has a low level of bacteria, said something? Could we be looking at a national problem?

          Our views are accepted in the scientific community.  ASHRAE also is aware of the data. However, the cooling tower link is so emphasized that it is difficult for lay organizations and public health authorities to acknowledge that the scientific view has shifted.

          The Wadsworth VA Legionnaires’ disease outbreak was initially linked to cooling towers by the CDC, but Legionella was subsequently found to be in the drinking water due to the potable water (Shands KN, JAMA 1985).  Other Los Angles hospitals specifically UCLA and Cedars-Sinai hospitals also experienced unreported outbreaks linked to potable water. Cedars-Sinai and Wadsworth have subsequently installed copper-silver ionization systems onto their water supply.

          The fact that it is in the drinking water of homes and apartment buildings has been reported in the scientific literature in many countries. Our studies were the first and the best-known reports and can be downloaded from Publications in our website (see Coming of the 3^rd Plague on the Home Page). CDC also subsequently linked drinking water to sporadic cases of Legionnaires’ disease (Straus W, Arch Int Med 1996).

          Public health agencies are reluctant to discuss this issue openly because of fear of panicking the population.  Reports in Europe and Australia have focused on cooling towers because it is easier to blame an outbreak on a cooling tower than on the public drinking water supply.  None of the reports you read about in the newspapers are ever published in the peer-review scientific literature, because the evidence for cooling tower links is so poorly supported.

          You may want to read our perspective in Stout, N Engl J Med Jan 16, 1992 on our comments concerning cooling towers and our response to the letters that followed (Yu, N Engl J Med, June 18, 1992). The Stout article can be downloaded from the Publications Section on www.legionella.org.  Click onto Mode of Transmission and download two articles by Muder Arch Int Med 1986 and Yu, Am J Med 93. Read the article on the Home Page by Yu.  Nosocomial Legionellosis, Current Opinion Infectious Diseases 2000.

          We predict that most published reports of cooling tower outbreaks will ultimately be shown to be erroneous.  Virtually all the articles on hospital outbreaks linked to cooling towers were published in the early 1980's. Interestingly after we published the first report showing the real culprit was drinking water in 1982 New England J Medicine and 1983 Lancet, subsequent outbreaks have been linked to drinking water.  The most publicized cooling tower outbreaks involved cooling towers at LA Wadsworth VA Medical Center, Rhode Island Hospital (Brown Univ), and Burlington Hospital of U Vermont; the actual source is now known to be drinking water in those hospitals.  In the early days the CDC never cultured the hospital water because they did not realize Legionella could be there.

       Pittsburgh hospitals have the highest usage rate in the world of the Binax urinary antigen and the only city in the world in which every hospital has Legionella cultures available for pneumonia patients.  Because of the intense interest in Legionella and the lab capabilities of Pittsburgh hospitals, the city of Pittsburgh has recorded more cases of Legionnaires’ disease than 38 US states.  In 1993, the

Allegheny County Guidelines (which can be downloaded from the home page of www.legionella.org) recommended culturing drinking water systems of hospitals, and disinfection, if necessary. By 2001,19 Pittsburgh hospitals had installed copper-silver systems. By 2001, cases of hospital acquired Legionnaires’ disease Legionella had all but disappeared from Pittsburgh.  In Pittsburgh, cooling towers are neither tested for Legionella nor disinfected.

       In 1992, we reported that Legionella could be contracted from the drinking water of homes and workplaces and warned all public health agencies that before cooling towers were blamed, the homes and the workplaces of the patients should be cultured to see if the real source was the drinking water.  CDC confirmed the accuracy of our report to their surprise (Strauss, Arch Int Med 1996), but they have not rescinded their cooling tower recommendations.  And, cooling tower outbreaks in hospitals have all but disappeared from the scientific literature. In a review of hospital outbreaks since 1985, virtually all epidemiologic investigations now implicate drinking water.  UK investigators were unable to link reported cases of community-acquired Legionnaires' disease to cooling towers in Nottingham, but found 39% of cases in Nottingham had Legionella in their home waters supply.  They concluded that home water supplies were the major sources in Nottingham (Lim WK, Epidemiol Infect 2003).

What is the best procedure for preventing Legionella becoming a problem in my hot tub. I currently use chlorine as a disinfectant but I am concerned that sometimes this runs out and I understand that the bacteria can build up in the air injector lines, also if there is chlorine in the water and Legionella builds up in the air lines is the Legionella killed off when the air is turned on when it passes through the chlorinated water

    Legionella must be in contact with the active biocide (chlorine, bromine, etc.) for a sufficient amount of time and at a concentration of the biocide that is active against Legionella.  So, control of Legionella would occur in the liquid phase.  Maintain the biocide concentration at the recommended level, monitor your biocide levels and keep the system clean.  This should keep your system under control.

       We also believe some of the outbreaks attributed to hot tubs were incorrect and the drinking water was the actual source.