General Public


Legionnaires' disease is a global public health issue. According to CDC's Morbidity and Mortality Weekly Report (August 2011), Legionnaires' disease increased 217% between 2000 and 2009. The disease-causing bacterium, Legionella pneumophila, is a waterborne pathogen found in natural and man-made water systems. Both potable and non-potable (utility) water supplies harbor Legionella pneumophila, and have been linked to outbreaks of both hospital- and community-acquired Legionnaires' disease.  

Ask The Experts

The following FAQs provide general and technical information about the disease. If you can't find the answer you're looking for, please click Ask the Experts tab and submit your question.

Disease Sources

Can I get Legionnaires’ disease from using a hot tub?

We have an inflatable hot tub that we filled up with a hose. Ran and used it for 5 days at 104 degrees. Did not realize that this disease existed. Did not have chlorine in the water. What is the likelihood that we have been exposed or will develop illness? Our family of 8 has used it daily. Most days without the bubbles going if that affects the possibility.

You describe a hot tub that is used intermittently and sometimes without chemical treatment. Typically, hot tubs would be treated with either chlorine or bromine to reduce bacterial growth (particularly Legionella pneumophila and Pseudomonas aeruginosa). The practice of intermittent use and no disinfectant would increase the risk of bacterial growth in the hot tub and thereby increase the chances of infection after use. For Pseudomonas skin infection (folliculitis), symptoms would occur soon after use (2-4 days). For Legionella, symptoms of respiratory infection can begin in 2-10 days after exposure.

Is it possible for an aircraft humidifier to spread Legionella?

Is it possible for an aircraft humidifier to spread Legionella? The humidifier is comprised of a glass fiber distribution pad with specially designed water channels that are moistened via spreader system to cool and humidify the air passing over it, utilizing the technology of evaporative humidification. When dry air passes over the moist surface, the water evaporates and the air is humidified while being cooled. There is no sump involved in the system and any excess water leaves via a drain port.

Evaporative cooling generally presents less risk for Legionella transmission. If the water supplying the system is potable cold water and not stored in any tank prior to use, it is unlikely that Legionella would grow in that water.

What is the risk of contracting Legionnaires’ disease from a wood cookstove?

I have an old-fashioned wood cookstove (cast iron) in my log cabin which I visit on weekends. There is a “water jacket” on one side, a tank that you put water in to humidify the air (and, in the old days, to heat water for washing clothes, etc.) The lid has a few holes in it, or you can open the whole lid. When the fire is hot, the water gets quite warm, and steams, but doesn’t boil in the tank. This weekend we made the first fire of the season. When I lifted the lid on the water tank, I saw to my dismay that some of the water had not been emptied in the spring. There was about an inch of standing water in the bottom. There is no spigot, unfortunately (which is why it’s easy to forget to empty it), so I began to ladle it out into a bucket. Got most of it, and then started to get nervous about bacteria / Legionella and so I poured a large pot of boiling water into the tank to hopefully kill everything in the remaining water. Let it sit for a little while, lid closed, and then when it had cooled a bit, ladled it all out and cleaned the tank as best I could with vinegar (tank is now dry). The water was still steaming when I was ladling it out. I wore a mask while ladling it out, but there was steam in the air and I didn’t wear a mask before or after removing the water. Also, the woodstove is in a dark corner of the cabin, nowhere near the sun. Even in summer, it doesn’t get too hot inside. Maybe 80 degrees Fahrenheit tops.

1. What is the risk if my husband or I inhaled some of the steam from the mix of old and boiled water? We are both very healthy non smokers in our mid 50s. And we obviously didn’t drink it!

Risk of exposure would be low given the description you have provided.

2. In general, should we use this water tank for humidity? The water often sits in the tank for many days while a fire is going, or if we leave before the fire is totally out. Is this unsafe?

Since you have access to the water, you could check the temperature. If above 140F/60 C Legionella would not survive.

What is the risk of contracting Legionella from using dormant water in the shower?

You mentioned on the website that showers are not a source of transmission. Is this true even if the bathroom steams up? Sort of confused about what constitutes “aerosolization”. Asking because we are only in the cabin on weekends and want to know if the shower is a risk (we have a UV system to disinfect the water and a regular hot water tank), but sometimes aren’t there for a few weeks.

Dormant and unused warm water systems could harbor Legionella especially if water temperatures are not hot enough. Here is an article that we published on residential water systems for your interest Legionella pneumophila in residential water supplies: environmental surveillance with clinical assessment for Legionnaires’ disease .
Showering was disproportionately emphasized as a route of transmission for Legionella– especially in hospitals. Here is another article that showed showering was not a risk Nosocomial, Legionnaires’ Disease: Aspiration as a Primary Mode of Disease Acquisition .

Can I get Legionnaires’ disease from wearing a face mask?

Is it possible to get Legionnaires’ disease from wearing a face mask or wearing a cloth face covering that hasn’t been washed?

You cannot contract Legionnaires’ disease from wearing face masks. Legionella bacteria is transmitted by aspirating drinking water or breathing in water droplets. Legionella  is not spread from person-to-person in respiratory droplets nor does the bacteria survive on dry surfaces. Your mask would not be a source of transmission for the Legionella bacteria.

Drinking from a water fountain in a hospital with Legionella in the water?

I visited a hospital and drank water from the faucet in one of the bathrooms. The hospital has found Legionella in the water. They, say they’re working to control this bacteria. As of today, I feel ok. Do I have to take any measures?


Water in most large buildings contains Legionella. Drinking water poses a risk to only select individuals. Lung disease and smoking are risk factors. Underlying immune-deficiency diseases or organ transplant recipients are also at higher risk. If you have a history of pneumonia or you are a cigarette smoker, you should avoid drinking tap water. Instead, boil water, let it cool and then refrigerate it for drinking. Since you do not have any of these risk factors, you are at little risk and you need not worry.

Can Legionnaires’ disease be contracted from decorative fountains?

Have there been any confirmed cases of Legionnaires’ disease being caused by water droplets from a decorative fountain?


Would it help if I added bleach to this water? (I do not use bleach in the fountain water since we have three cats)? If so, how much would I need to add to it and how often?


A few cases of Legionnaires’ disease have been linked to fountains, but the risk is low. The bleach probably would be helpful. The concentration is 1-2 parts per million, but it would corrode your fountain. Using boiled water after it has cooled would reduce the risk to zero.

My home water is infected with Legionella.

Our home water supply is infected with Legionella. I am really concerned. I don’t drink tap water, but do I have to worry about showering, using the dishwasher, washing my clothes, and brushing my teeth?


We have found that the risk of acquiring Legionnaires’ disease from your home water system is quite low. Generally, those who have contracted the disease from their home water systems are usually smokers.


Legionella can be isolated from a small percentage of residential water systems. If the bacteria is present, the risk of disease to the average person (with no serious underlying illness) is extremely low. It is also likely to be found in water faucets as well as showers. The role of showers in the transmission of Legionella is overemphasized. Elevated hot water temperature (about 130°F or 55°C) can minimize the chance that Legionella will grow in a water system. Consideration should be given to the risk of scalding to small children and impaired adults if the water temperature is set at this high temperature.


With respect to your question, there is no risk with use of a dishwasher, washing clothes, and showering. For immunosuppressed patients, we recommend that tap water not be drunk. It is theoretically possible to contract Legionnaires’ disease from brushing your teeth with tap water.

Growth temperature of Legionella for hot water tanks?

What is the minimum temperature in water that Legionella does not grow? (Ex: 150°F, 143°F) I need to know this to promote prevention of Legionella for the water heaters I sell. Is this the best method for prevention?


Legionella will not propagate at temperatures of 140°F (60°C). When the hot water leaves the tank, the temperature will drop. So, be aware that if Legionella is already in the distal sites such as pipes and faucets, the increased hot water temperature will not affect the Legionella elsewhere in distal sites. Maintaining hot water temperature at 140°F is not an effective method of disinfection for large buildings for that reason. However, if a systemic disinfection is carried out beforehand, (e.g.: superheat and flush or copper-silver ionization), hot water tank temperatures of greater than 140°F may minimize recolonization.

I work in a building which has Legionella in the water.

The building I work in has tested positive for Legionella bacteria. One individual fell sick last week. What are the risks to me if I keep showing up for work and inhaling the air conditioned air? Do you think I should leave?


Some hot spots were found in the building, two in air conditioning water cooler towers and one in a ladies bathroom sink, one floor beneath me. An outside Legionella risk management company came in to the building to conduct independent testing and found no Legionella bacteria present in the water supply. Then, the City Health Department conducted their tests; Legionella was present and potent. Is there still a risk if the building has been cleaned? Can you please give some direction. No one is telling us anything.

It is not well-known to the public that Legionella in large building water supplies is commonplace. The fact that Legionella was found in the workplace water systems of a sick person does not necessarily mean that this was the source of infection. If the Legionella organism was isolated from the patient, molecular typing can be done on both this organism and the Legionella recovered from the water systems. If they match, then there is a stronger probability that the workplace was the source.

The reason for not being overly concerned is that unless you have an immunosuppressive underlying illness or smoke cigarettes, you are at little, if any risk. Healthy individuals have many potential sources for exposure to Legionella in the community, as well as from home water systems. Although we understand your concern, no guidelines on workplaces or public buildings have been formulated because the risk is so low.

Cooling tower outbreaks in the news. What is the explanation?

I am a journalist working for Norwegian TV. In the city of Stavanger in Norway, there has recently been several cases involving Legionella, and investigations conclude that cooling towers most probably are the sources of this outbreak. On this site 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.


Should my condominium association routinely culture for Legionella in the water?

I need your advice. My condominium association has received a proposal from a company to check our water for Legionella on a quarterly basis. As far as I know, we have had no cases. My inclination is to say no, but I want to consult an expert.


The brief answer to your query is don’t culture buildings unless the building houses a high risk group of individuals (chronic lung disease, immunosuppressive illnesses, illnesses requiring chemotherapy/transplant rejection meds/corticosteroids).


The rationale is:

  1. Miniscule attack rate. Please see the article by Pedro-Botet on Coming of the 3rd Plague. We do recommend that convalescent care facilities housing a notable number of debilitated patients culture their water supply once a year. See Seenivisan, J Amer Geriatrics Society 2005
  2. Maintenance measures directed at water supplies colonized with legionella are not evidence-based; in fact data from our lab shows that virtually all recommendations involving maintenance do not affect Legionella colonization.


So, what should the residents of your condominium association do to prevent Legionella infection?

1) Smokers should quit smoking.

2) High risk groups should not drink tap water. Tap water should be boiled, then cooled and refrigerated for drinking for high-risk patients. See Singh, Transplant Infect Dis 2004


I contracted Legionnaires’ disease from a dental procedure.

I am a 15 year kidney transplant patient on immunosuppressants. I was diagnosed with Legionnaires’ this past weekend at the hospital. After reading the literature about ways of contracting this disease, I believe there is a good chance that I contracted it from a dental visit earlier in the week. My dentist uses a water cooled drill. I had a severe coughing episode when water entered my throat.

Dental procedures involving water have the potential of transmitting microorganisms including Legionella. Your dentist and any other doctor you see should know you are a transplant patient on immunosuppressive medications. You should inform the dentist of your concern. I would recommend culturing the dental water supply.

Epilogue: Although the dentist gave us permission to culture his dental water supply, he disinfected the dental lines beforehand. And he refused to allow our technician to culture the water tank of the facility since the tank would still have harbored the Legionella even if he disinfected the water line.

Do fish ponds cause Legionnaires’ disease?

We have been notified that a fish pond with Japanese carp will have to be cleared due to the health risk of Legionnaires’ disease. Is it not possible to eliminate the risk in such a confined public area? If the pond has to be cleared, wouldn’t all outside ponds need to be cleared?


Although Legionella may be found in extremely low numbers in natural aquatic bodies of water (like a pond), there is little opportunity for amplification (growth) and transmission. We are not aware of any reported cases of Legionnaires’ disease associated with natural ponds. So, we see little risk of contracting Legionnaires’ disease and would not be concerned. No guidelines for ponds, including fish ponds, have been formulated with respect to Legionnaires’ disease. On the other hand, rare cases of Legionnaires’ disease have been linked to natural hot springs.


Legionella was found in the tanks underneath the swimming pool.

I work in a leisure centre which has just been shut to the public because they have found Legionella in the tanks underneath the swimming pool. We have been told that the staff can stay in the building and work because it is not in the water supply e.g. showers etc. Nobody at work is convinced and we feel we should not be in the building. Can you tell us if it is safe as we are concerned for our health?


The information given above is inadequate to answer your question. Who frequents the leisure center and has a case of Legionnaires’ disease occurred in this center? Assuming that the patrons of the leisure center are the general population and that a case has not occurred, it is probably safe to enter and work in the building. It also may be safe for the public. Legionella poses the greatest risk to patients with risk factors such as smoking, who may be exposed to contaminated drinking water.


Can a hot tub transmit Legionella?

My husband, 52, is a non-smoker, previously healthy, and has contracted Legionnaires’ disease. He has been very ill from it. He uses our hot tub almost daily. I recently swapped out the filter with the alternate filter which I store in an outdoor shed. Also, our pool maintenance man added a floater for the tablets which he had stored at his home. I do not use the tub often, however, before having knowledge of this diagnosis on Sunday, I used the hot tub and now I have a deep moist cough but no fever. I do not want to drain the tub without first discovering if it is the source of LD. How do I go about getting it tested and then how do I effectively disinfect the tub? Of course, I plan to discard both the filter and the floater.

We are skeptical of some reported outbreaks linked to hot tubs. We also know that Legionella can be acquired simply through the home drinking water. But your question is a reasonable one. If you husband has confirmed Legionnaires’ disease, then the physician is required to report the case to the local health department. The health department can decide whether or not to culture the hot tub.


Can swimming pools transmit Legionella?

Is there any data about contracting Legionella from swimming pools especially if they have not been used all winter long?


The risk from contracting Legionnaires’ disease from swimming pools is negligible.


Could a dental night guard soaked in water be the source?

The Health Department conducted a limited phone survey, but did not come to the house for an inspection. We have been advised that I probably inhaled or aspirated some standing water. After 3 weeks, I am back to work, but my strength and stamina are low. We are trying to determine the source of the Legionella so we can take corrective action.


I would appreciate your thoughts regarding the two likely sources in our home:

1) A portable air conditioner that has a 1/2 liter reservoir to catch the condensate. The instructions say to pour this accumulated water down the drain whenever it gets full, which is about once a week during the summer. One week before I got sick, I began to clean this air conditioner and noticed the reservoir had developed a pink mold. I poured out a small amount of water into the sink. I then vacuumed and cleaned the insides of the air conditioner, so I could store it til next summer.


2) I use a dental night guard every night; it is a formed plastic mold of my teeth that keep me from grinding my teeth. I store it in a glass of water every day, and sometimes I forget to change that glass of water for a week or more. Maybe I pulled the night guard out of the “dirty” water and went to bed. Sometimes I cough after putting it in my mouth, and maybe some of the water went down the “wrong pipe” and got into my lungs (aspiration).


The air conditioner is not the likely source.

The dental night guard soaked in tap water may be the source. This can be proven by culturing the home water supply and the “dirty water.” If the health dept will not provide this service, we can do it gratis if the Legionella has been isolated from culture of your sputum. Otherwise, merely use boiled water for storing your dental guard. Let it cool before dropping your dental mold into it.


Can my home’s water heater harbor Legionella?

My roommate was just diagnosed with Legionnaires’ disease. About 10 days ago, our hot water heater had to be replaced. Our landlord typically buys them secondhand. Could the not-so-new water heater be the source of the bacteria?


My roommate is on Humira and Methotrexate to treat rheumatoid arthritis so his immune system is compromised. Many thanks for your time!

The information that you have provided is insufficient to answer your question. It is theoretically possible that your roommate could have contracted Legionnaires’ disease from you home water supply, but the hot water heater is not necessarily the cause. Legionella was likely in the drinking water prior to installation of the heater.

See the article Coming of the 3rd Plague

You can ask your health department to culture your home water supply for Legionella. If they cannot or will not do it, it is possible that we could assist. Before we can do that, we need confirmation from your roommate’s physician that the diagnosis of Legionnaires’ disease is absolutely correct and we need to see the actual lab test result. In the meantime, your roommate should not drink tap water.


FYI – We recommend that transplant patients and highly immuno-suppressed patients do not drink tap water. Instead, boil water and cool it for drinking. When traveling or not at home, bottled water might be preferred.

River water used for power plant cooling system?

I work in a power plant and we use river water in our cooling 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.


Air conditioners as a source of Legionella in the United Kingdom?

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 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 center 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.

Emergency showers and eye-wash units?

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.


Can dry steam cleaning machines kill Legionella?

I have been asked to clean bathroom tiles and shower heads in a chain of hotels. Will dry steam cleaning machines kill this bacteria? Would ordinary steam cleaning machines kill this bacteria?


Heat above 170°F and drying will kill Legionella. However, bathroom tiles, even when wet, will not transmit Legionella. So you need not worry about Legionella in that situation.


Disinfection of non-potable water?

I have installed a 550 gallon black plastic water tank to provide water to a cabin. The tank will become very hot in the summer sun. The water will be used for bathing, washing, flushing, but not for drinking. It has been suggested that this might not be a good idea because of Legionella. Could I add anything to the tank water to help? It has been suggested that I add fresh water on a regular basis. The source is a creek that is fed by springs in the Texas Hill country.

Place a warning that the water is not for drinking. You could also disinfect the water with chemicals such as bromine. In addition to bromine, a small amount of bleach (free chlorine) can be poured into the tank for residual disinfection. You should calculate the amount of bleach added. The final concentration of free chlorine should not exceed 1 mg/L.

The idea of adding fresh water into the tank is to provide residual chlorine from the “fresh water” into the tank as disinfectant. If you use the creek water, then it will not solve your potential problem.

Air conditioners are not a source for Legionnaires’ disease.

I want to disinfect the part of my window-unit air conditioner that is exposed to the outside. I’ve always been worried about Legionella in air conditioners. I have used a shark steamer several years in a row to clean this part of my AC unit. I figured the extremely hot steam would kill bacteria on contact. Was I right? 


You are thinking and trying to find an innovative solution using logic. And your hot steam may kill bacteria. However, despite conventional wisdom, air conditioners are not a source for Legionnaires’ disease.


Robotic showers?

My company makes Robotic Shower Sanitizing Systems. We are presently evaluating re-engineering a current product as an On-Demand (Automatic) Shower-Head and Dead Leg Sanitizing/Cleaning System. However, literature suggests that weakened immune system patients cannot get Legionella from bacteria in the shower-head mist. Is this true? Thank you.


Sterilization on shower heads is unnecessary. You are correct; showering is not a mode of transmission for Legionnaire’s disease. Sterilization of a distal site, such as faucets, is ineffective. The Legionella forms biofilms in the pipes leading to the faucets, and showerheads. If the system is infected with Legionella, the water will still contain Legionella.


Air conditioners and amoxicillin?

Can a person become infected from the warm air which is expelled by large industrial air conditioner fans?


Also, would Amoxicillin (500 mg, 3 per day) over seven days cure an infection?


We do not believe that air conditioners play any role in Legionnaires’ disease. Amoxicillin is ineffective against Legionella.


Can a dishwasher be a source for Legionella?

We moved into our house a year ago. We haven’t used the dishwasher yet and I am concerned about contracting Legionnaires’ disease if we use it. Do you have any testing advice? Is there a cleaning technique that will work, or am I worrying too much?


Dishwashers do not transmit Legionella. There is some conjecture that homes with dishwashers are less likely to harbor Legionella in the drinking water, because the temperature of the hot water system required for dishwashers is not conducive to Legionella growth.


Fish tanks and Legionella risk?

I work in a skilled nursing facility and we just placed a 50 gallon fish tank in the center of the building. What risk factors, if any, should we be aware of concerning Legionnaires’ disease and how can we minimize the risk? Thank You


The mode of transmission of Legionella is aspiration (which requires drinking water) or aerosolisation. A fish tank would not easily fulfill these 2 conditions, so it would carry minimal or no risk of contracting Legionnaires’ disease.


Showering is not a risk for Legionnaires’ disease

My elderly mother has a guest bathroom that hasn’t been used in six months. I am concerned that the shower and faucets need to be flushed before anyone uses them, in order to avoid Legionella. The water temperature, at the faucet closest to the water heater, with a regular food thermometer, was 138°F. The shower is the farthest faucet from the water heater.


If I flush the water lines, do all faucets in the house have to be flushed? How many minutes? Should I wear a mask? Should the family leave the house? Can the Legionella spread to the tub and shower curtain and throughout the house? Your expert advice will be greatly appreciated.

Showering is not a risk. Our contrarian view has credibility since I was a co-author of the first report that suggested showering was linked to Legionnaires’ disease. We were wrong, and we will publish info that refutes the issue of showering as a risk factor for contracting Legionnaires’ disease. So nothing is needed for your elderly mother with respect to showering.

If she smokes cigarettes, persuade her to stop. Smoking is a legitimate risk factor.

Legionnaires’ disease from a hotel?

My brother is in hospital and Legionella has been found in his urine. Does this mean he has Legionnaires’ disease?


Probably yes. Just out of curiosity, is your brother in a Hurricane Sandy zone?


No, he is in a hospital in Ontario, Canada. At age 78, he became ill while in Hilton Head, was driven home where he was hospitalized. He has been diagnosed with bacterial pneumonia, is incredibly weak and at times is disoriented with low-grade temp. Thank you for your help.


The source of your brother’s Legionella is in the Hilton Head hotel. Inform US CDC or ask your Health Department to do it. This infectious disease syndrome has a name: “Travel-associated Legionnaires’ disease.”

BTW, if your brother is a smoker, he should quit now.

Finally, Canadian hospitals have capable physicians. I assume he is being treated with azithromycin or levofloxacin. If he is improving – fine. If he is the ICU and deteriorating, he should get the following 3 drug regimen: Rifampin (3 days only), Azithromycin, Levofloxacin.

Good luck!


Are car wash employees at risk for Legionnaires’ disease?

If a car wash had its washing station contaminated, do the people working in the car wash need to be tested for Legionella?


The employees only need to be tested if they see a physician because of symptoms of fever and cough.


Will black mold cause Legionnaires’ disease?

Can black mold that has been in the basement of our apartment for a few years cause Legionnaires’ disease?


My friend has had pneumonia for a while. My fiance has severe memory loss, chest pains, and disorientation. My brother and I have had horrible headaches, memory loss, disorientation, and chest pains. I also looked at other pages on this website and I saw that some of our symptoms are symptoms of Legionnaires’ disease.


Molds in homes do no cause Legionnaires’ disease. You should see a doctor about your symptoms.


Cooling towers or drinking water?

I read “Cooling tower outbreaks in the news. What is the explanation?” in a section of the FAQs on this site. I don’t understand the following part of your reply to the question about asking 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.”


What does this mean? Why should I doubt the investigators?

The entire reply is:

“Public health authorities downplay thre 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 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.”

The implication is that the actual source is not the cooling tower, but the home or workplace of the patients with Legionnaires’ disease. In order to be thorough, the health department should have cultured the drinking water that the patients had been exposed.

See the Publications section for more information. Here are two publications that address this issue.

Cooling towers and legionellosis: A condundrum with proposed solutions


Legionnaires’ Disease Contracted from Patient Homes: The Coming of the Third Plague?

Filtered water as a source?

Could a person have contracted the disease from rinsing water left in the sink too long?


Alternatively, could the person have contracted the disease by drinking water from a water tank which has three filters and then put in a water purifier?

Possibly, yes. Fresh tap water may also contain Legionella.

Concerning the water tank, if the filters are designed to catch bacteria and the purifier can kill bacteria, these may be effective in keeping the water pure. Many filters and purifiers are unable to stop bacterial contamination. You have to read the fine print on the product.


Is dental water the source of infection?

My husband and I have lived in the same apartment complex for a year. The water system was worked on prior to my husband getting Legionnaires’ disease. He works for the county as a utility worker and his recent job was to use a 6 foot flame torch wand powered by an air compressor. He blows debris, sand, water, etc. out of the cracks in the street. He always wears a shield to protect his face. He has been doing this work for about a month now.

At the beginning of February, he went to the dentist for a crown. The 2-14 day incubation period would have been from 2/3-2/16. In that period, he was admitted to the hospital and diagnosed with Legionnaires’ disease. He has been in the hospital for a month now, with two of the weeks in critical care. The CDC is unsure what the source may be. What scenario is the most plausible for contact with Legionnaires’?


The dental water is the most likely source. You now have a number of options. Show this message to your local health department or the CDC. They may or may not investigate. You should show this to your dentist as well, and ask him to contact us through our website or by telephone. We would culture the dental water to confirm the source and suggest disinfection methods to resolve the issue.


Flushing home taps to remove Legionella?

I have two questions:

1) I am about to clean up a bathroom that has not been in use for four months. Would flushing the taps for ten minutes get rid of any Legionella? It is on the second floor of a two story detached house. Should I take any other precautions?


2) Can the air conditioning system in cars ever contain Legionella?

Flushing out the stagnant water is not a bad idea, but not particularly effective against Legionella, since Legionella is in the biofilm encircling all the pipes and fixtures. A brief flushing for several minutes is ok if the water is to be used for drinking.

The risk to individuals living in a home with Legionella in the water system is almost nil if you are in reasonably good health. If any of the residents of the home have a chronic disease, we recommend that tap water not be drunk – either in the home or elsewhere. Recommendations are to boil tap water, cool it, and store it in a pitcher for later drinking.

There are two reports in scientific literature suggesting that air conditioners in cars might cause Legionnaires’ disease. We are highly skeptical of the validity of either report.


Hot water tanks in apartment blocks?

We have an apartment in a block of twenty apartments. Our apartment is only used several times per year. In each apartment there is a hot water tank. Are we at risk of contracting Legionella if the hot water tank is used only when we visit the apartment? Sometimes this can be months.

The risk for contracting Legionnaires’ disease from residences and apartments is very small. The risk probably does not come from stagnancy or decreased usage of the water heater; the risk comes from the characteristics of those individuals staying in the apartment. For example, elderly cigarette smokers, those with chronic lung disease, or those with immune status deficiencies (transplant recipients).

The only way to know for sure is for us to test the water in the apartment. I wouldn’t bother unless:

1) There are high-risk residents living in the apartment

2) A cases or cases of Legionnaires’ disease are occurring in your apartment block.

If you want us to test, let us know – we will send you test kits and instructions.If cases of Legionnaires’ disease have occurred, we will perform the tests gratis (if your Health Dept cannot do so).

I suggest that you not worry about it.

Risk from home tap water?

I have been living in house for over four months with a hot water heater that is not the proper temperature. My landlord will not get a water heater mixing valve. I am very concerned about Legionella. I have been very sick for months with nausea and diarrhea.

I worry because I am eight months pregnant and I also have a ten month old. I drink this water every day and also use it for my son’s formula bottles. What should I do, and how much danger are we in?

The danger of Legionella infection from your drinking water is negligible unless your are a cigarette smoker or have an immunosuppresive condition (transplant recipient, cancer chemotherapy, etc).

The danger for your baby is also negligible; however, since you are making formula, merely use water that has been pre-boiled.


Legionella in home refrigerator?

My refrigerator at home has a clogged freezer drain. As such, a leak started from the freezer into the fridge below. We put a cake pan which we empty regularly about 1 time per week. However my 3 year old ended up drinking some out of that tray because we were out of water bottles and she didn’t tell us like she usually does. Is it possible to contract Legionella from your home refrigerator? Should my wife or I be worried about exposure as well?

I would guess that little risk, if any, would occur from drinking water from that tray. If your health seems okay now, I would surmise no harm has been done from drinking this water. To be certain, consult your physician.

Risk of Legionnaires’ from various water sources?

1) Would a clogged roof drain leaking into an office pose a non-risk, low risk, or high risk of causing Legionnaires’ disease in a worker in that office?


2) Would a drinking fountain (lower than 68°F) be a suspect source? What if the temperature was not always maintained below 68° (water was above 68° but then returned below 68°)? Could the water be contaminated even though it is now below 68°?


3) What is the likelihood of contracting Legionnaires’ from a bathroom faucet when washing hands?


4) If bottom of hot water heater is much cooler than the upper layer of water, which is what goes into the hot water system, why would the lower water be of concern? 


5) If the hot water heater is off for a few days, then is back on and delivering water at 122°F-140°F, could the water at the faucet still be contaminated with Legionella?


1) Non-risk

2) It would be a low risk. Temperature becomes a factor mainly when it is between 120°F – 140°F, the optimal temperature for propagation of Legionella.

3) No risk.

4) The temperature is conducive to growth of Legionella mainly between 120°F – 140°F. If the hot water tank was at this temperature, it is possible that it could become contaminated.

5) Yes