Transmission of Disease


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.



Transmission of Disease

Risk of Legionella from being sprayed in the face?

I was sprayed in the face with water that had been sitting in the pipes of the spa for about 10 days. I immediately washed myself thoroughly, went to the doctor and he prescribed erythromycin for 12 days. This is my 5th day on the antibiotic and I haven’t shown any symptoms. I am normally a healthy person. Should I be worried about the possibility of having contracted the disease?


The mode of transmission is usually aspiration. Aerosolization can also transmit Legionella, but the aerosolization must be intense. For example cooling tower drifts and air conditioners, despite the publicity in newspapers, rarely, if ever, transmit Legionella. The few studies in peer review journals almost never consider other likely sources including potable water from residences or workplace and culture selection is heavily biased towards cooling towers. Vapors from water devices colonized with Legionella can transmit Legionella. So, being directly sprayed with water is unlikely to cause Legionnaires’ disease. The use of erythromycin essentially reduced a minute risk to zero.


Please inform your physician that erythromycin is no longer the drug of choice for Legionnaires’ disease. Other drugs (azithromycin, clarithromycin, levofloxacin, ciprofloxacin) are more potent and have fewer side-effects.

Risk of a newborn baby from contracting Legionella?

We have rented a vacation condo for June, at which time one of the members of our family will be a four month old baby. There have been recent reports of Legionnaires’ disease in this condominium building. Will it by safe by June to take my newborn there, and are newborns more at risk of contracting the disease?

Legionella is contracted most commonly by aspiration of water containing Legionella. You probably have consumed Legionella in drinking water for years without contracting Legionnaires’ disease. The individuals with greatest risk in the general population are elderly cigarette smokers. The risk to you and your newborn is extremely low. Newborns have been reported to contract Legionnaires’ disease, but almost always in the hospital where the hospital water supply is contaminated.


Can children contract Legionnaires’ disease?

Are children under the age of 2 years at risk of contracting Legionella? If they do contract the infection what is the prognosis or mortality?

Children do, indeed, contract Legionella. The ones at greatest risk are immunosuppressed (e.g. transplant recipient, receipt of corticosteroids) or those hospitalized (especially neonates). In the hospital, the disease is contracted by Legionella in the drinking water. The mortality in reported cases was 33%.

If you are a physician, we can send you a preprint of details of the 76 children who have contracted LD. If you are not a physician, you should know the risk is extremely low.

Will masks protect us from Legionnaires’ disease?

We are planning a trip overseas. We will be in the cabin of an airplane for over 18 hours. Should we wear a mask to avoid Legionnaires’ disease?

Legionnaires’ disease is not transmitted person-to-person, so you need not be worried. Masks are useful for some pneumonias, but not Legionnaires’ disease.


Can Legionella infect animals?

Can Legionella infect animals?

Elevated serum antibody levels have been found in horses. A fatal case of pneumonia due to L. pneumophila was diagnosed in a calf. However, only 1.7% (2/112) of the other cattle in the herd had serological evidence of exposure to Legionella (antibody blood test). The disease was linked to exposure to a hot water system colonized with Legionella.

Fabbi M, Castellani-Pastoris M, Scanziani E, et al. Epidemiological and environmental investigations of Legionella pneumophila infection in cattle and case report of fatal pneumonia in a calf. J Clin Microbiol 1998; 36(7):1942-1947.


What can I do to increase awareness of Legionnaires’ disease?

I have personally been infected by Legionnaires’ disease. What can I do to increase awareness of this infection so that others could be spared this terrible disease?

The most important problem that we face as physician researchers in this field is that a startling amount of misinformation is present and scientifically validated information that would allow prevention of this infection is not disseminated by public health authorities. It is a fact that Legionella is commonly found in the drinking water supply of large buildings.

Since the discovery of the source of the organism in 1982 (Stout, N Engl J Med 1982), this important fact has not been exploited for prevention. Most public health authorities are not interested because of the panic and media exposure that it may bring. Likewise, hospitals are afraid of negative publicity, overlooking the fact that if patients learn that they contracted the infection from being admitted into a hospital that did not check their water supply for Legionella that they would not only sue, but they would win.

The one thing that you can do if you have contracted Legionella from a hospital is to ask the following question. Did the hospital have a preexisting policy to culture the water supply? This approach is recommended by the Maryland state health department and Allegheny Health Department (Pittsburgh). However, Denmark, France, and Barcelona, Spain have also established guidelines for hospitals to culture their water supplies. In 2003, after much foot-dragging, the CDC recommended that all hospitals performing bone marrow and solid organ transplants should culture their water supply. Unfortunately, many cases occur in non-transplant patients. Regardless, we feel that all hospitals should culture their water supplies. CDC has argued in the past that it’s expensive, but culture material, including formulation of the Pittsburgh media, is now commercially available, and the cost for materials is probably less than $500 a year. Nevertheless, they have balked at this recommendation.

Hundreds of outbreaks from hospitals have been reported. Nosocomial (hospital-acquired) Legionnaires’ disease is now commonplace and has become a well known complication.

Approaches for preventing any patients from contracting the disease within a hospital have been published by the State of Maryland and Allegheny County (Pittsburgh) Health Departments. Both health departments recommend that the hospital water supply be cultured for Legionella. If Legionella is found, the physicians are informed so that if the patient contacts pneumonia while in the hospital, tests for Legionella should be immediately available in-hospital. This is a matter of common sense. Moreover, if many of the water sites are positive (for example, greater than 30%), the hospitals can disinfect their water supply. Copper-silver ionization is now the most widely used modality and there are a number of reputable manufacturers for such devices.

Inexplicably, a major obstacle to this approach is the Centers for Disease Control in Atlanta, Georgia, which has been very slow in moving forward on this issue. In 1993, CDC guidelines actually discouraged hospitals from performing routine environmental cultures. They claimed that the evidence was insufficient despite that fact that several hundred reports had documented that Legionella could be contracted from hospitals including their own investigations. One of their reasons (which has been convincingly refuted) is that since the organism is ubiquitous, it could exist in hospitals without harming the patients ( Yu VL. Resolving the controversy on environmental cultures of legionella. Infect Control Hosp Epidemiol, 1998). We and others now have presented data to show that as many as 70% of hospitals. In some cities harbor Legionella (in San Antonio, the number is 100%); this information is critical to disseminate to physicians in the affected hospitals.

In summary, the current approach throughout the world, with some exceptions, is to ignore the problem altogether.

My friend with leukemia has contracted Legionnaires’ disease.

My 5 year friend got leukemia and is now in maintenance chemotherapy phase. Do you have any data about the effects of Legionella on such patients? What the best way to avoid the infection?

With the exception of hairy cell leukemia which has a disturbingly high incidence of Legionnaires’ disease, leukemia is not a major risk for Legionnaires’ disease except for the time they spend in hospitals.

The greatest risk comes from hospitals that have Legionella in the hospital drinking water, but are unaware or do not want to be informed of its presence. A few hospitals test their water supply for Legionella, and their patients are safe. Unfortunately, most do not. The CDC now recommends that hospitals in which bone marrow transplants are performed should culture their water supply. We recommend that immunosuppressed individuals not drink tap water, but water that has been sterilized by boiling and then cooled.


Can Legionella be contracted by eating?

Can Legionnaires’ be ingested and give symptoms of nausea and vomiting and migrate to the lungs via the digestive route?

Your scenario above is not quite correct, but close. Click on About the Disease and there is some discussion on Aspiration. Nausea, vomiting, diarrhea can occur. The Legionella bacterium, enters the lung not through the digestive tract, but is aspirated through the windpipe (trachea).


Can Legionnaires’ disease be caused by mold?

I had new piping put in my house and the plumbers didn’t do the job right. Mold formed inside the house in three of the bedrooms and I became sick with pneumonia. It was later diagnosed as Legionnaires’ disease. Can Legionnaries’ disease be caused by mold? Or affect the air conditioner in my house where the spores would be spread around the house?

Legionella can be contracted, not by mold, but by the water in your home water distribution system. Your doctor is required to report your case to the Health Department, perhaps, they may culture your drinking water for Legionella. If you live in Pennsylvania, Ohio, or New York, these Health Departments will do this free for you in collaboration with our laboratory.

Although air conditioning is popularly thought to be linked to Legionnaires’ disease in the original 1976 American Legion outbreak, it is now known the source may have actually been the hotel water distribution system. The role of air conditioners in disseminating Legionnaires’ disease is not supported by scientific studies.

Can mold be a precipitating factor for Legionnaires’ disease?

I had a severe asthma attack at work yesterday. The air conditioning system was not used during the summer months throughout the classrooms. The remodeled building was made for air conditioning therefore many areas are closed off to the outside and there are no windows. I was in such a room for 6 hours. I spoke with the janitors about the possibility of a mold problem because that was what triggers my asthma. They told me that they have been chasing after mold on pipes that carry the cool air into the building all summer. The mold keeps returning on pipes and blower units. One janitor told me that the mold looks like moss hanging from a tree…hanging on a pipe. They have brought in an outside firm to wipe down the pipes. School starts in a few days. Could this scenario be a breeding ground for Legionella? What do I need to look for when I get into my classroom?


The scenario that you describe is not likely to include Legionella as a risk to healthy students and teachers. As is described elsewhere, air conditioners are not likely disseminators of Legionella. Legionnaires’ disease has not been linked to mold contamination.


My goldfish died. Could it be Legionnaires’ disease?

My goldfish died last week. I thought I overfed it. But, an outbreak of Legionnaires’ disease occurred at a large aquarium in our country (Australia). Could my fish have died of Legionnaires’ disease?


We think you overfed the goldfish.


Legionella in compressed air systems?

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.


Do you recommend banning patient showers on transplant units?

Legionella has been found in our hospital and the water supply was successfully disinfected with copper-silver ionization. Nevertheless, showers for our transplant patients have been banned. This is a major inconvenience for patients and nursing staff. If, as you claim, aerosolization is not the mode of transmission, why should showers be banned? Our engineering staff also monitors showerheads by removing them and cleaning them with disinfectants although this is done on an erratic basis.

Showers are not important disseminators for Legionella. Our view has credibility since Dr. Victor L. Yu was a co-author of the article published in the Annals of Internal Medicine 1981 that suggested Legionella might be transmitted via showers. Subsequent case-control studies showed our original conclusion was erroneous, although no retraction has ever been published. Subsequent studies from  Belgium, Netherlands ,  University of  Virginia, Wadsworth VA Medical Center, University of Iowa, Lackland Air Force Base,  University of  Pittsburgh, and  University of  Arizona also showed this conclusion was erroneous. The article by Sabria in Lancet Infectious Disease 2002 gives an overview of the studies. Most (but not all)  U.S. transplant centers have quietly rescinded their ban on showering and cases of Legionnaires’ disease attributed to showering have not occurred. We agree with this policy.

Studies also show that disinfection of showerheads by chemicals or cleaning is ineffective long term given the fact that Legionella recolonizes the showerheads from existing biofilms in the pipes of the plumbing system.

Legionnaires’ disease and travel?

Recently we have witnessed an increase in the number of patients diagnosed with legionella in our district. Apart from the known risk factor for legionellosis (smoking, diabetes mellitus, and immunocompromised states) we noticed that 30% of them became ill after flying from or to the country from different areas. The entity of travel-associated legionella is well known but I would like to hear your opinion regarding the possible influence of traveling itself, especially by air, upon the susceptibility of the exposed people to develop disease.

I do not believe that  travel itself, either air or otherwise, plays any direct role in the acquisition of legionnaires’ disease. I believe that the risk factor is the large buildings, e.g., hotels or cruise ships in which the drinking water is colonized with Legionella  to which the traveler is exposed. The solution is not easy since only a small fraction of individuals who stay at these hotels contract Legionnaires’ disease, and that they may also be exposed to drinking water colonized with Legionella from buildings other than hotels. If a significant increase in  travelassociated Legionnaires’ disease is being seen in your district, a study should be performed by your Health Department noting the characteristics of the patients (cigarette smoking is more important than diabetes) and the sources of drinking water to which they were exposed.

Will filtration be effective for my home water?

I have read recently that home hot water pipes may be a breeding ground for Legionella. Is there any kind of filtration system for the home that would solve this or is boiling the only remedy?


You may want to read the paper on our web site “Legionnaires’ disease contracted from patient homes.” Unless you are at increased risk of contracting Legionnaires’ disease (chronic lung disease, immunosuppression, transplant recipient), you are at such a low risk of becoming infected that there is no need for any action on your part. For individuals at high risk, we recommended increasing the hot water temperature to approximately 60oC (140oF) max. setting on the hot water tank and flushing the outlets for 30 min. with the hot water. This can be done on a quarterly to annual basis to reduce the level of Legionella within the system. However, this procedure is unnecessary for most homes. There is a risk of scalding with water at this temperature, so caution must be exercised if elderly or small children use the water.

Filtration would be expensive because the filter would have to remove particles the size of bacteria (0.2 microns) and they would have to be changed frequently.


I contracted Legionnaires’ disease in the hospital.

I contracted Legionnaires’ disease in a hospital. They sent me home with a low-grade fever and a cough. 1 week later my daughter found me on the floor of my bedroom, unconscious and covered in feces. I was taken to the hospital by ambulance and admitted into ICU, where 3 days later they diagnosed me with legionnaires’ pneumonia. What I don’t understand is why the hospital was not held responsible for my illness (they did a test on their HVAC system and found Legionnaires’ in the water). 

It is possible that the hospital water distribution system was the source of the Legionella. You should contact your public health department for information; they might have cultured the hospital water supply.

Homework on Legionella

I have looked on the CDC website and searched many sites about Legionnaires’ disease. I have questions for my report but can’t get any answers from anyone. If you can help me that would be fantastic! Was Legionnaires disease ever categorized as an epidemic or pandemic? What are some ways Legionnaires Disease was treated in the past? Was there a scientist credited with finding a cure or vaccine?

To answer this question, you have to know the definition of pandemic. If you can’t figure it out, then guess. You have a 50% chance of getting it right. The cure is antibiotics. No one scientist found the cure. The right antibiotic was found by trial-and-error. Our research group conducted the clinical trials and published the medical articles that led to approval of azithromycin and levofloxacin by the FDA for treatment of Legionnaires’ disease.


Legionella and pregnancy

I know that they said a pregnant woman’s fetus is safe from the bacteria, even if the woman ingests/breathes in infected water, however, what about from the point of conception until the placenta is in place? Are there any risk factors during this 2 week period of time? Could bacteria create any problems with getting pregnant? Thank you for taking my questions.


Infection during pregnancy is not a good event, in general, from a common sense viewpoint. And, pneumonia can have adverse effects for mother and child. However, only one case, to our knowledge, has been described in which pneumonia led to death of the fetus – this was a report by Italian investigators. In 2 cases of Legionnaires’ disease in pregnant mothers, antibiotic therapy was curative for the mothers, and the 2 babies that were subsequently delivered were healthy. So, fetal death due to Legionnaires’ disease is extremely rare. Some infections such as rubella (German measles), measles, cytomegalovirus infection, and bacterial meningitis are causally linked to fetal defects and adverse effects long-term for the child (e.g. deafness, mental retardation). This has not been the case for Legionnaires’ disease. Keep in mind that the highest avoidable risks for Legionnaires’ disease are those who smoke cigarettes. So, quitting smoking during pregnancy is good for both child and mother. In response to your last question, Legionnaires’ disease has not been linked to infertility.

Follow Up Question:

Thank you for your quick response. To clarify, the only way that it’s even a remote possibility of danger to the fetus (from conception forward) is if the mother actually comes down with the disease? If I’m ingesting or breathing in this bacteria and my body is healthy and therefore, successfully fights it off, there is no risk to the fetus?

Follow Up Answer:

Yes. No danger exists for the fetus if the mother is healthy. The risk to the fetus is probably not so much invasion by Legionella, but that the pneumonia causes respiratory compromise or shock to the mother. For reality purposes, I think that the risk for an unborn baby to be harmed is so close to zero that neither you nor any other healthy expectant mother should be concerned.

This confidence comes from:

  1. Experience – no one in the world has seen more cases of Legionnaires’ disease than we – and we have never encountered a case. On the other hand, we have encountered directly or indirectly cases of Legionnaires’ disease in infants, children and mothers in maternity hospitals. In these few cases, the infection was delivered directly to the infant or child by the water; however, the Legionella was not passed through the placenta to an unborn baby. We are also the authors of the first comprehensive report of Legionnaires’ disease in pediatrics and in 2006, we sounded the warning to infectious disease specialists and pediatricians to alert them that infants and children could contract Legionnaires’ disease ( Lancet Infectious Diseases, 2006). This article can be downloaded from the Publications section. I wouldn’t bother, however – it is for pediatricians and not for laypersons – you might freak out.
  2. Logic and extrapolation. We are authorities on hospital-acquired (or building-acquired) Legionnaires’ disease. Legionnaires’ disease has occurred in women’s hospitals and children’s hospitals from the drinking water. Despite this vast experience, we know of no cases of fetal harm in a healthy mother. (Nor would we ever expect such a case).


In short, rest assured that you and your baby are safe.


Will Legionella survive on dry surfaces?

We are going to dismantle a water feature that we were told contained Legionella. The fixture has been dry for almost two months. I am concerned that when we tear the fixture apart, the bacteria will become airborne and be inhaled. Can Legionella survive out of the water for that length of time?

Legionella will not survive on dry surfaces. Although inhalation is popularly believed to be a mode of transmission, it is rarely transmitted through the air. Drinking contaminated water and “aspirating” the Legionella is actually the most common mode of transmission.

In any case, no danger exists from contracting Legionnaires’ disease in the circumstances that you described.

Risk of Legionnaires’ from fire-fighting equipment?

I have recently assumed maintenance responsibility of fire-fighting systems in multi-use buildings with sleeping accommodations. The buildings have standard fire-fighting hose reels fed from the main water supply, which is ambient temperature. These are tested monthly by releasing water through the nozzle to waste. Annually, they are tested by allowing water to flow at full pressure for two to three minutes.


We have fixed and portable water mist fire-fighting equipment. Both systems have pressure of 100-110 bar with droplet size of 70-100 micron. The water storage tank capacity is 250 liters, and the portable systems have a capacity of 25-50 liters.


Is there a definable risk of transmission of Legionella in the use of these systems when fighting a fire or testing the equipment?

No cases of Legionnaires’ disease have ever been reported with respect to aerosols from spraying from hoses. Although aerosolization is considered a mode of transmission for Legionella, in actuality, the major mode of transmission is aspiration associated with drinking contaminated water. I wouldn’t worry about transmission from fire-fighting equipment either during active fire-fighting or maintenance of equipment.


Infectious dose of Legionella?

What is the infectious dose of Legionella causing food infections?


Legionella does not cause food infections.

Follow-Up Question:

What kind of disease does Legionella cause then?


Legionella causes pneumonia, a lung infection. Diarrhea can be a common symptom because the transmission is from contaminated water. However, the mode of transmission is aspiration, not aerosolisation as is commonly believed.

Follow-Up Question:

So if a person drinks water with Legionella, what is the infectious dose that will make them sick?


The infectious dose for contracting pneumonia is unknown, but it will be much lower than the infectious dose for typical food borne infections since the Legionella is aspirated directly into the lung.


Legionnaires’ disease in mothers: Can it have an effect on the fetus?

What happens if a pregnant woman contracts Legionnaires’ disease? What will happen to the fetus? I know she cannot be infected by other people, but could she contact the bacteria and contract the disease?


Legionnaires’ disease is a pneumonia that is often severe with a high mortality rate, if the pneumonia is not diagnosed early. The risk to the fetus can be high for 2 reasons:

1) The mother can be severely-ill with a life-threatening disease. This would in turn threaten the life of the fetus.

2) The Legionella bacterium could cross the placenta and infect the fetus. This would likely harm the fetus and may cause permanent damage. This scenario should be discussed with the obstetrician and we can email him/her information on outcome and therapy. Please show the doctor this email and ask the doctor to contact us.

If the mother was diagnosed early in the course of pneumonia, the antibiotics that are effective cross the placenta and would protect the fetus. These antibiotics are not harmful to the fetus with one exception: doxycycline may cause some problems. However, the more effective antibiotics (macrolides such as azithromycin, clarithromycin, erythromycin) are not harmful to the fetus. The quinolones  (levofloxacin, moxifloxacin, ciprofloxacin) are also highly effective and are not considered harmful to the fetus, but clinical experience is limited. Cartilage damage might occur in infants, but no such cases have been reported in fetuses.

Legionella transmission from a fan?

Can Legionella be contracted from a dirty damp carpet with a blow fan heater on it for a number of days in an enclosed room?


Theoretically, this may be possible, but it is extremely unlikely. I wouldn’t worry about it.


How can I prevent myself from getting Legionnaires’ disease?

What is the best way to protect ourselves from Legionella pneumophila or just Legionella in general?


For patients who are in general good health, the best protection is to avoid cigarette smoking.

For patients who have an underlying disease that compromises their immune system (diabetes, kidney failure, etc.), avoid drinking tap water. Instead, bring the water to a boil, then cool it, and then store it in the refrigerator for drinking. Long boiling times are not necessary. As soon as the water starts boiling and bubbling, Legionella and other water bacteria are killed. Bottled water is less likely to contain Legionella in large numbers than tap water.

For patients who are transplant recipients, receiving cancer chemotherapy, or receiving corticosteroids (prednisone), tap water should not be used for drinking. Buildings taller than three stories are more likely to harbor Legionella.

Risk of Legionella in pipe to my fridge?

I am looking to install a hard water pipe to my fridge. The current supply is soft water. The pipe in place is approx. 15 feet long under concrete. If I cut and blank this pipe, is there a risk of Legionella contamination?


Rather than address your question about any added risk for the water pipe to your fridge, I merely will inform you that the risk from contracting Legionnaires’ disease in your own home is lower than the risk of contracting Legionella of any large building of greater than three stories.

First, Legionella may already be present in your home. But the percentage is very low, especially if you have a dishwasher for which the water temperature is above that for Legionella survival. Second, you and your family likely have little risk for Legionnaires’ disease if you do not smoke. Third, you are exposed to tap water containing Legionella on a daily basis since Legionella is present in many large buildings.

In the unusual circumstance that your or a family member have ever contracted Legionnaires’ disease, we would check the water supply of the home by culturing for Legionella and then advise you. In your case, the additional risk caused by installing this pipe is probably zero. In short, install your pipe to the fridge and don’t worry about it.

Transmission by aspiration?

I was directed to your site through the bibliography in Protect Yourself from Legionnaires’ Disease, by Matt Freije. Your conclusions regarding transmission of the disease differ significantly from the book and other sites I have investigated, including material at the CDC. Given the interesting hypothesis, your site states that the most common mean of transmission is through aspiration. Could you please explain how this could account for the large outbreaks that have occurred, such as in Pittsburgh and other cities throughout the world?


My wife contracted what was diagnosed as Legionnaires’ in New York. While the blood and urine tests were both negative (she was not able to produce sputum to culture), the infectious disease specialist diagnosed the disease based on x-rays of the chest and other symptoms. We have an apartment in New York that we use as a second home. When I contacted the New York Department of Health, they recommended having every faucet, showerhead, and air conditioner in the apartment tested. Do you advise that we follow through with this? We received an estimate of $1800, but I am highly skeptical that this would be worthwhile. I am understanding through other FAQs on your website that there is no probability of someone contracting the disease from showers or faucets, as well as air conditioners.


Finally, a friend of mine read some research that Legionnaires’ disease cannot be reconstructed by a person that has already had it. I haven’t found any other information that confirms this. Do you have an opinion?


Thank you very much.


The issue of aspiration versus aerosolisation and drinking water versus cooling towers/air conditioners is a controversial one that can best be answered by using evidence based medicine and scientific data. If you have a scientific background, you can read these following two articles and judge for yourself.

1) Cooling towers and Legionellosis: A condundrum with proposed solutions.

2) Mode of transmission of Legionella pneumophila: A critical review.

One circumstantial piece of evidence is that our scientific group remains premier in Legionnaires’ disease. Individual advocates of aerosolisation and cooling towers have disappeared – it is difficult to make a longterm contribution if you are in error.

Large outbreaks have not occured in Pittsburgh – that is where we are! (There was a recent outbreak at the Pittsburgh VA, but that was due to neglect and poor maintenance practices – not misinformation). Pittsburgh, PA has more documented cases of Legionnaires’ disease than most US states due to active surveillance!

The reason cooling towers have been identified is due to one simple fact. It is obilgatory for any outbreak to culture any putative sites. The cooling tower outbreaks never culture the drinking water! If that is done, the drinking water is always found to be the source. So, should you spend $1,800? No, save your money. (If you want to spend it, our Special Pathogens Laboratory can culture your water. We usually will perform these cultures gratis for home residents, but we require that blood and urine tests document the presence of Legionnaires’ disease.) If you wife is taking steroids or immunosupressive medicines, she should avoid drinking tap water. Note that in the US, transplant recipients are advised not to drink tap water. Instructions are giving on on boiling tap water, and then cooling it for drinking.

Your friend is correct. Although we have seen more cases of Legionnaires’ disease than anyone in the world, we have only seen one patient who has experienced a recurrent case of Legionnaires’ disease. So it appears that some immunity to Legionella may occur. This infor is not in the medical literature, it is on our website.


Recurrence of Legionnaires’ Unlikely?

I had Legionnaires’ disease in 2007 at the U of M in Michigan. Can get the disease twice?


The crawl space in my house is very damp and I am not doing so well. I am a smoker, and I have had several health problems like bicuspid aortic valve, aneurisms, and so on.

The answer to your question is uncertain. However, based on our experiences with patients (we have the largest experience worldwide), we have observed only one patient who contracted Legionnaires’ disease a second time.

If you want to minimize the the chance of recurrence, don’t worry about your damp crawl space and don’t worry about air conditioners and hot tubs; they have nothing to do with Legionnaires’ disease. This information is on our website. Instead, quit smoking!! This is the most important risk factor for Legionnaires’ disease. And smoking causes heart disease and cancer as well!

Temperature of water supply to the shower?

I have secondary progressive Multiple Sclerosis and have a lowered immune system, so i have a scenario and question.

I live in a new council apartment in West Yorkshire and my water temperature is limited through the taps and shower. My kitchen tap is 45.8°C, the bathroom tap is 43.6°C, and the shower is 39.8°C. The shower is what really concerns me but the council just will not agree to raising the temp. I have a Potterton Pro Max Combi-boiler and obviously don’t have any water storage but this is my concern and I would like your opinion please.

My concern is that even though water temp through to the shower control unit is probably around 43.6°C from the Thermostatic mixing valve it only then produces the 39.8°C water which is the ideal temp for Legionella to thrive. My point has been two fold. When I go on respite for 4 weeks, because of the low temp it becomes a possibility that Legionella can breed and infect me. Then because the temp will NEVER be hot enough to kill off any bacteria it will just grow and grow.

Am I correct in making this assumption? I just have to be ultra-cautious because of my lowered immune system and something like this could be really bad for my wife and myself.


Your assumptions are not quite correct.

Please review our website FAQs and do a search on the top right hand of the Home Page.

Showers are not a major mode of transmission. Setting your thermostat higher may not be effective if Legionella is already in your home water supply.

A simpler more effective solution is given in the Publications.

Legionnaires’ disease contracted from patient homes: The coming of the third plague?

The solution to your question is on page 704, second to last paragraph.

Aspiration vs swallowing water?

If I swallow water contaminated with Legionella pneumophila and the water goes to my esophagus instead of my trachea because I don’t aspirate, can I still get Legionnaires’ disease although the bacteria didn’t enter my lungs?

Good question.

The answer is no. That is the reason so many patients who are exposed to water with Legionella don’t contract Legionnaires’ disease. The ones who do contract Legionnaires’ disease tend to have risk factors for aspiration – the most notable of which is cigarette smoking.


Leigonella in our summer home?

I was at our summer home in upstate NY with my father. Three days later he was admitted to ICU and tested positive for Legionella & E. coli. The results of his culture have not been completed yet.


I have done some extensive research online about Legionella. I have also recorded everything he was doing prior to being admitted. From what I know, the environmental conditions seem apparently ripe for L. pneumophila as well as L. longbeachae. He was drinking well water with high iron content, worked near a fresh-water stream, he had an open wound on his hand working with soil, he was sawing rotting wood by back door and not wearing a mask. I recall the smoke detector going off, so he was inhaling what seemed like thick heavy saw dust. There was also lots of rain around this time as well.


He is 76 yrs old and has had CLL for the past 10-12 yrs and for which no treatment has been required. I know that L. longbeachae is not that prevalent in the USA. Does this strain need to be tested for specifically? If it is the L. pneumophila-type could he have developed the infection from the open wound in his hand by taking a bath?

We will need a bit more info.

Is your father a cigarette smoker?

What were his whereabouts in the 12 days prior to becoming ill? That is, how many days did he display symptoms prior to seeing a physician?

What were his symptoms? Did he have diarrhea?

What was the name of the laboratory test that showed he had Legionnaires’ disease? Was it a urine test?

What was the antibiotic used to treat him and when did he get his first dose? Was the first dose given in the hospital? What is the name of the hospital?


My father did not smoke cigarettes but he did occarionally smoke a pipe. He arrived in Upstate NY on July 8th. He was admitted to the ER at NY Presbyterian Weill Corenll Hosp. on July 20th.

Upon admission he given a dose of ceftriaxone. His symptoms were shortness of breath, mild cough, green productive sputum, occasional sweats, and a fever of 38ºC. He did not complain of diarrhea.

Upon testing positive for Legionella and E.coli by urine antigen on July 22nd, he was treated with azrithromycin, vancomycin, and zosyn. A sonogram of the kidneys on July 23rd revealed renal failure, and dialysis was started on evening of July 25. To date, his mental status is not alert but improving.

I was with my father until the evening of July 16th. He did mention around July 15th that we has feeling a bit of malaise, more tired, and had low energy. He generally doesn’t like to complain of being sick and did not give me any indication of something more. When I phoned him on July 18th, he said he had a headache and was feeling a bit tired and weak and that he would be going to sleep. I noticed his speech seemed slurred. On July 20th, my cousins stopped by and said he looked pale, and was running fever and could hardly walk.


Azithromycin is curative, and it appears that your father is recovering.

Some patients feel rundown and tired for a few months after recovery from their pneumonia. Since your father is recovering, I would hope that the kidney failure is transient, and that this problem is also resolving; kidney failure is common in untreated Legionnaires’ disease.

The source of the infection is most likely drinking water. Inhaling dust and having an open wounds are not risk factors for Legionnaires’ disease. Many healthcare workers including physicians believe aerosolisation (breathing water droplets) is the mode of transmission.  It is not – drinking the water (aspiration) is the way Legionella is transmitted.

Recommendations for the future:

Your father should never drink tap water. Boil tap water, cool it, and save it for drinking. This is applicable everywhere including restaurants or other homes. Bottled water is safe (although the supporting data is limited).

The heat and flush procedure would disinfect the mobile home water, but would need to be repeated at periodic intervals.