Infection Control


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.  

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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.

Infection Control

CFU/mL as a guide to remedial action?

A technical bulletin from PathoCon Laboratories has a table with suggested Legionella Remedial Action criteria. They list various detectible limits of CFUs/mL as a guide for remedial action. For example, 109 CFUs may require cleaning and/or biocide treatment of equipment if indicated in potable water. Do you have any current information or references with action level based on CFU’s/mL.

It is logical that the overall burden of Legionella within the water distribution system should correlate roughly with the risk for contracting Legionnaires’ disease. While cfu/mL quantitation seems to be an intuitively plausible concept, in actuality, our studies showed that quantitation is highly variable. One reason is that Legionella resides within a biofilm coating in each pipe or distal fixture. When repeat samples are taken from the same site within a short period of time, the cfu/mL may vary widely. Also, water usage at that site and frequency of sampling from that site can also affect cfu/mL.

In short, no evidence exists to show that quantitation is useful for predicting risk, but considerable data exists to show it is an inherently unstable method. The recommendations from our website are evidence-based so we would not use this table as a guideline for remedial action. In contrast, the percent distal site positivity does correlate with occurrence of disease.

Monochloramine in the water supply and the need for hospital monitoring for Legionella?

What would you recommend as a monitoring program for our hospital given the fact that our municipality is using monochloramine. We perform environmental cultures for Legionella on a regular basis. Our distal water sites are consistently negative. Our laboratory also has Legionella culture and the urinary antigen test to be used for both community-acquired and hospital-acquired pneumonia.

Regarding your Legionella monitoring program, we congratulate you on having diagnostic capability in-house. Many hospitals still send these tests out to reference labs and as a consequence, the physicians do not use the tests, because it takes too long to get a result. Given that your municipality is using monochloramine and that you have a history of negative culture results from your distal outlets, we would recommend that you revert to performing environmental monitoring once a year.

Is routine environmental surveillance the standard of practice?

Is environmental surveillance becoming a standard of practice in most hospital settings?

The following countries now recommend routine environmental surveillance for Legionella in hospitals: Denmark, France, Germany, Taiwan, and in addition, the cities of Barcelona, Spain; Pittsburgh, PA; and the State of Maryland. U.S. CDC recommends routine surveillance if transplants are being performed at that hospital.


Frequency of Legionella monitoring in hospital water?

What frequency would you recommend for monitoring Legionella in hot water systems of hospitals?


At least once a year if there are no cases. See the algorithm in ACHD Guidelines in the Guidelines Section. Use the results of the environmental cultures to assess the risk of Legionnaires’ disease at your facility.


Can we allow showering in the hospital?

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.


Preventing Legionnaires’ disease in long term care facilities?

Do you believe there is a benefit to residents in LTC facilities in identifying Legionella infections? What interventions can LTC facilities implement to prevent and manage these infections.


There is clearly a benefit to identifying Legionella infections in long-term care facilities. In the absence of an influenza or respiratory syncytial virus outbreak, most pneumonias in long-term care facilities are due to aspiration of the bacteria colonizing the patient’s pharynx. Indeed, many studies have identified swallowing difficulty, tube feeding, and other markers for a tendency to aspirate as major risk factors for pneumonia in this population. Prevention is problematic, since the underlying problem is inability to protect the airway.

Legionella infection, on the other hand, is acquired from the environment. If there is no Legionella in the environment, then disease cannot occur. Thus, unlike most types of pneumonia in the long-term care setting, Legionella is highly preventable. In addition, most patients in long-term care facilities are treated for infection without benefit of specific microbiologic diagnosis. In the case of pneumonia, this is particularly true, since sputum samples are notoriously hard to obtain in this population. A diagnosis of Legionnaires’ disease permits specific, pathogen directed therapy, and avoids overly broad empiric therapy (identified by many experts as a particular issue in nursing homes).

Our specific recommendation would be to perform surveillance cultures for Legionella on the facility’s water system. If L. pneumophila serogroup 1 is identified, patients with pneumonia are easily tested with Legionella urinary antigen. This would provide a basis for a rational decision on whether or not to perform eradication procedures. See article by Seenivasan JAGS 2005.


Decorative fountains in hospitals?

Our hospital installed the attached fountain in our new lobby, contrary to the department of infection control’s recommendation. It recirculates the water from the pool to the top where it dribbles down the rock face. Has legionellosis ever been shown to be caused by such a fountain? What would your recommendation be regarding assessing the fountain directly for Legionella?

The evidence that decorative fountains are a disseminator for Legionella is surprisingly weak. That said, we discourage installation of fountains in hospitals because of the anxiety that such fountains bring when Legionella outbreaks are attributed to such devices. However, in this particular case, it appears that the design is not one of intense aerosolization with spraying water. So, the risk of contracting Legionella by aerosolization is exceedingly low.

Legionella species other than L. pneumophila in our hospital water supply?

We perform environmental testing for Legionella in our hospital water supply. If Legionella that fluoresces under UV light (bozemanii, gomanii, dumoffii, anisa, cherri, steigerwalti, gratiana, tucsonensis, parisiensis, rubrilucens, and erythra) are found, should the water system be disinfected? Is there any relationship between these species and infection to humans?

In general, if no cases of Legionella have been discovered due to these non-pneumophila species, you do not need to disinfect. If cases due to these species are found, disinfection should be initiated if two (2) conditions are both fulfilled:

1) Immunosuppressed hosts especially transplant patients are being hospitalized at your facility

2) Distal site positivity is >30% for that Legionella species.

Rising transesophageal probes with hospital tap water?

Our facility (hospital) has Legionella in its water system and cases of hospital-acquired Legionnaires’ disease, and there currently is a prohibition against drinking the hospital water. All patients are getting their water via bottled water. Is the fact that TEE probes (transesphageal echo) are being rinsed with hospital tap water a problem for infectivity?


This is an important question that you have raised. You are correct. Sterile water should be used for rinsing TEE probes. Please inform your Infection Control practitioner that sterile water must also be used for rinsing nasogastric tubes and respiratory tract equipment. Interestingly, there is a report of 3 cases of hospital-acquired LD transmitted by TEE probes (Levy PY, Infect Control Hosp Epidemiol Aug 2003).


Legionella and refrigerated water fountains?

Have you heard of any linkage to Legionella associated with refrigerated portable water fountains or coolers? Is there any information or guidance about flushing refrigerated water fountains on a routine basis to decrease risks?

Many years ago, there was a dramatic increase in the concentration of Legionella (and a shift in species) isolated from our chilled drinking water system. Our usual experience was to find low concentrations of L. bozemanii (blue-white fluorescing species rarely associated with infection). Then one day our water fountain cultures were covered with (>3000 cfu) with Legionella pneumophila, serogroup 1. The compressor/chiller had malfunctioned a few weeks previously and that a new one was on order. This system was a recirculating system with 2-3 fountains/floor on this system. After the chiller failed, the water was no longer cold enough to inhibit Legionella pneumophila from growing in the system. We did try to hyperchlorinate the system, with the expected result-recolonization after a few weeks. Ultimately, we replaced the old recirculating system with stand-alone units. Now we rarely have a positive culture from these units and the water is very cold.


First draw water samples for Legionella culturing of distal water sites?

Our approach to culturing environmental samples in our hospital is to collect 1 liter water samples from a tap after the water has been run until it gets “hot”–some sites may take several minutes before the sample is collected. After looking at our numbers, and reading about different ways to collect the sample, I realize that we probably are NOT getting a good representation of the distal site, but more of what is present centrally. We prefer to collect water rather than swab so we can get a quantitative number (I did read your paper recommending the swab as the more sensitive though!–I am concerned that there may be a great deal of variability in how a swab would be collected). Would it be better for us to collect the sample immediately after turning on the tap, and collecting a smaller volume? We really can’t do an immediate and a post flush– we have a difficult enough time having the state lab to handle one sample/site!

One liter samples are not necessary. Our experience and studies have has shown that the first draw sample is a more sensitive sample than a “post-flush” sample. In addition, we sampled approximately 100ml, and plated 0.1 mL directly and after concentration by filtration (100mL filtered and resuspended in 10mL). We validated this method by performing a multi-center study and correlated site positivity with disease incidence using this method (article in press). You are correct that variability in quantitative counts exist for swabs, but variability also exists for water. So, quantitation is simply too variable to be useful.


Legionella gormanii and L. pneumophila, serogroup three, in the hospital water?

Legionella gormanii and L. pneumophila, serogroup 3 are in our hospital water supply. In a newly constructed hospital (280 beds) we have detected the presence of Legionella in the hot water system only after a few months. The results of the samples collected immediately after commissioning were negative.


After 5 months, the routine surveillance of the water quality revealed a weak contamination of the hot water distribution system with L. pneumophila serogroup 3 (< 1000 cfu/l). To our surprise we found Legionella gormanii (concentrations between 1500 and 12000 cfu/l) on several water outlets in patient rooms (like wallmount faucets and thermostatic shower valves).


We have never heard of this species. By reviewing the literature, we found only 2 articles: First isolation of Legionella gormanii from human disease – Griffith et al. – 02/1988. Legionella gormanii sp. Nov. – Morris et al. – 11/1980. Is the virulence of L. gormanii comparable to that of Legionella pneumophila?


Legionella gormanii is one of the avirulent Legionella species, although cases of infection have been described. Isolation of this species from your water supply is not a major cause of concern. L. pneumophila serogroup 3 is also a species that has rarely been implicated in disease. So, you probably need not disinfect your system if the only organisms are L. pneumophila serogroup 3 and L. gormanii. Ideally, all patients with hospital-acquired pneumonia should be cultured for Legionella. The urinary antigen will detect only L. pneumophila, serogroup 1, and cannot detect L. pneumophila, serogroup 3, or L. gormanii. If Legionella cultures are unavailable, perhaps a quinolone should be added to cases of hospital-acquired pneumonia that do not have a clear-cut etiologic diagnosis.


Two reviews of Legionella gormanii are in the Publication Sections of


Fang GD. Disease due to the legionellaceae (other than L. pneumophila): historical, microbiological, clinical, and epidemiological review. Medicine 1989;68:116-132.


7 cases of L. gormanii are reviewed in this article.


Muder RR. Infection due to Legionella species other than L. pneumophila. Clin Infect Dis 2002;35: 990-998.


Regulations for maintenance of hospital water supplies?

Are the normal regulations and planning rules applied for system design (temperature > 55oC, no dead legs or stagnation, circulation loops, maintenance, monitoring, etc.) sufficient to control the presence of Legionella in the hot water systems?


Download Lin’s articles on Disinfection in the Publications section. None of the measures mentioned including maintenance or removal of deadlegs affect legionella colonization! Maintaining hot water temp at > 55oC is effective for a period of time only if a superheat and flush was performed previously.


Length of time for cultures of Legionella to be positive?

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.


Is Legionella anisa in the hospital water a concern?

Is Legionella anisa in the hospital water a concern? 

Legionella anisa is a fairly common environmental species. In a recent survey we have found that about 20% of hospitals in the US are colonized; the number of reported cases of infection is extremely low. There is a reported outbreak of non-pneumonic legionellosis (“Pontiac Fever”) due to L. anisa occurring in an automobile plant due to contaminated, aerosol generating equipment. There is limited laboratory evidence to suggest that L. anisa may be somewhat less pathogenic that L. pneumophila, at least based on an ability to infect mammalian cells.

The risk of disease after exposure to environmental L. anisa by healthy people, or the general hospital patient population is exceedingly low. It might be advisable, however, to protect highly immunocompromised patients, such as transplant patients, patients on high dose corticosteroids, from exposure.

Key references:

  1. La Scola B, Mezi L, Weiller PJ, Raoult D. Isolation of Legionella anisa using an amoebic coculture procedure. J Clin Microbiol. 2001 Jan;39(1):365-6. PMID: 11136802.
  2. Fields BS, Barbaree JM, Sanden GN, Morrill WE. Virulence of a Legionella anisa strain associated with Pontiac fever: an evaluation using protozoan, cell culture, and guinea pig models. Infect Immun. 1990 Sep;58(9):3139-42. PMID: 2117580.
  3. Fenstersheib MD, Miller M, Diggins C, Liska S, Detwiler L, Werner SB, Lindquist D, Thacker WL, Benson RF. Outbreak of Pontiac fever due to Legionella anisa. Lancet. 1990 Jul 7;336(8706):35-7. PMID: 1973219.
  4. Fallon RJ, Stack BH. Legionnaires’ disease due to Legionella anisa. J Infect. 1990 May;20(3):227-9 PMID:2341733.
  5. Thacker WL, Benson RF, Hawes L, Mayberry WR, Brenner DJ. Characterization of a Legionella anisa strain isolated from a patient with pneumonia. J Clin Microbiol. 1990 Jan;28(1):122-3. PMID: 2405005.
  6. Bornstein N, Mercatello A, Marmet D, Surgot M, Deveaux Y, Fleurette J. Pleural infection caused by Legionella anisa. J Clin Microbiol. 1989 Sep; 27(9):2100-1. PMID: 2778073.


Should the hospital water be tested for Legionella?

My mother entered the hospital with complaint of gastrointestinal problems. She was told by admitting physician lungs were clear. Three days later she was diagnosed with pneumonia. I have spoken with several families in ICU they state their family members entered hospital without any respiratory symptoms yet they developed legionella pneumonia. I would like some guidance on how to proceed to get this hospital water system tested, I fully believe she contracted the pneumonia in the hospital. How in the world can we get this water tested and what laws do physicians have governing their reporting Legionnaires’ disease in a hospital. Should the hospital water be tested?

It is a requirement that the hospital inform the health department of your mother’s case of Legionnaires’ disease. The CDC also recommends that when a case of Legionnaires’ disease occurs in a hospital, the hospital water supply should be cultured since this is a likely source. You should point this fact out to the doctor taking care of your mother. You can also call the county health department and ask that they investigate. You have asked an important question. I hope that the hospital has already taken steps to investigate.


Has media coverage had any adverse social impact?

Has the Legionnaire’s disease and its media coverage had any adverse social impact like did AIDS in the first few years of its discovery and then was understood better?

The impact of the lay media has been both positive and negative.

Negative: Bad publicity to a hospital or organization can result because the primary source is the drinking water; cooling towers or air conditioners are overemphasized by the authorities since the public is more alarmed by drinking water sources than by localized sources such as cooling towers. The truth can bring panic and a flurry of lawsuits.

So, hospitals often do not want to know about Legionella in their drinking water. Nor do public health agencies want to push this issue because of the inflammatory nature of the truth. On the other hand, we believe that knowledge about the hospital drinking water can allow preventive measures to be taken by the hospital and alerting the MDs such that the disease can be prevented or treated earlier.

Positive: Revelations by the lay media have stimulated many hospitals to take preventive measures. The best example is the 1998 TV exposè by New York City Fox news. Their reporters went into NYC hospitals and cultured legionella from the drinking water of most hospitals. Unbeknownst to the TV reporters is that in one hospital that was culture-negative in their report, Legionnaires’ disease had been discovered in the patients and the hospital water supply was the source.

Infection control for Legionella

What is the nurse’s role in surveillance of LD?

And, what are the primary prevention strategies for LD?

The primary and most effective preventive is routine culture of the hospital drinking water.

UK Legionella guidelines are not evidence based?

I work in the UK for a water hygiene company as an operative. Our Legionella control contracts include various buildings such as schools, offices, homes for the elderly, community spaces etc. I have long been skeptical of the effectiveness and necessity of some of the standard UK control methods (using ACOP L8 guidelines) and also the levels of risk we are led to believe exist. Finding your website has certainly been a revelation. Are you aware of UK Legionella control regulations i.e., health and safety at work act, and ACOP L8, and what would be your opinion/critique of these?


We are aware that the UK guidelines are not evidence-based. For example, they have taken our findings on temperature settings for water distribution systems and have incorrectly extrapolated them to recommendations to maintain hot water temperatures at certain levels – this recommendation is unjustified and has proven ineffective. They also use quantitative cultures cfu/ml as criteria for risk; this measurement has proven inaccurate. They also emphasize stagnation and recommend removal of dead legs; this recommendation is logistically-tedious and has not proven to be effective.

Could you send us the ACOP L8 Guidelines? We plan to review non-scientifically-based recommendations on later this year.

Question about Legionella?

I am a research manager for a company which produces and distributes cold water. The company has cooling tower systems in Paris. I have worked with the Legionella associated risks of these facilities for 12 years. In France, epidemiology experts have said that Legionella pneumophila is responsible for 98% of the cases of Legionellosis. They said that the facilities should control the concentration of Legionella pneumophila (instead of other species). However, in patients, the urinary detection of the disease can detect only Legionella pneumophila. This seems to be a strange conclusion. In Australia, they found that ~10% of Legionellosis is obtained by other species.


The other observation I have is that you think that it is possible to explain Legionella contamination by inhalation of Legionella from biofilms to the throat, and then it colonizes the lungs? A French person spoke about this once, and if I understand, you have issued this idea a few years ago?

In brief, we believe that the onerous regulations in France are misguided, wrong and contradicted by substantial scientific evidence.

Special microbiology of Legionella?

Would the health department be able to identify this microorganism by performing routine water-screening procedures, such as serial dilutions followed by incubation on EMB or TSA plates?

Standard microbiological media including EMB or TSA will not support the growth of Legionella. Special procedures and media are required for isolation and identification of Legionella. A few health dept microbiology labs do have this capability.


Cleanliness and maintenance for LD in hospitals?

I am a health protection practitioner working in the UK’s Health Protection Agency. I specialise in investigating and managing cases of Legionnaires’ disease. I am one of thousands who benefit from your work and regularly see your names when researching the subject.


This morning I found an old reference book in our library and was interested by your comments about the gap between intention to control and actual control. This is what you wrote: “It should be emphasized that appearance, degree of cleanliness, and regular preventative maintenance measures of the system were not associated with Legionella contamination. Thus, recent engineering guidelines and building codes directed at Legionella, although well-intentioned, are unlikely to affect Legionella colonization.”


(Yu, V.L., 1995. Legionella pneumophila(Legionnaires’ disease). INMandell, G.L., Bennett, J.E. and Dolin, R.Principles and Practice of Infectious Diseases,4th Ed. London: Churchill Livingstone.)


Given the long time since this was written I was wondering, has your current position on this changed?


Our position has not changed. However, more studies have been performed that show that many commonly recommended measures for Legionella prevention are not only non-evidence-based, but may actually increase the risk of Legionnaires’ disease.

See Publications for recent articles as well as the articles below.

Lin YE, Stout JE, Yu VL. Prevention of Hospital-Acquired Legionellosis. Curr Opin Infect Dis. 2011. 24(4):350-6

Lin YE, Stout JE, Yu VL. Controlling Legionella in Hospital Drinking Water: An Evidence-Based Review of Disinfection Methods. Infect Control Hosp Epidemiol. 2011;32(2):166-173.

Stout JE, Yu VL. Environmental culturing for Legionella: Can we build a better mouse trap? Am J Infect Control 2010;38:341-3.

Disruption of water distribution system and Legionella?

The city recently turned off water supplying my hospital, and then turned it back on a couple of hours later. My concern is that the sudden rush of water during the turning on of the water releases biofilms in the water system. Are there any recommendations on what to do within the hospital to those water lines?

Your concern is well-founded. Disruptions within the water distribution system have been linked to outbreaks of hospital-acquired Legionnaires’ disease.

The only way to assuage your concern is to culture the water distribution system of that hospital. Most US academic transplant centers and all hospitals in Maryland and Pittsburgh culture their distal water sites on a regular basis, as do all hospitals in Western Europe. If such a disruption occurred, the water system would be cultured to assess the potential of an influx of Legionella coming into the system. Short-term disinfection could be enacted, and the water re-cultured to ascertain the effectiveness of the disinfection.

You can express your concern to the Infection Control practitioner at your hospital.  The Association of Infection Control Practitioners (APIC) Manual recommends routine culturing for Legionella of the hospital water distribution system as an effective preventive measure for Legionnaires’ disease.

As an aside, our Special Pathogens Lab performs environmental cultures for many of the top healthcare centers in the US.

Flushing of toilets, shower heads, and faucets?

How often should showers/toilets/faucets be flushed in closed or unused areas?

Flushing of toilets is unnecesary. Showerheads are also over-estimated as a source of Legionnaires’ disease.

Faucets should be flushed, however for this to be effective, a disinfectant such as copper-silver or chlorine dioxide must be in the water. Copper-silver concentrations within the water distribution systems should be assayed every 2-4 months. Legionella positivity should also be monitored every 3-4 months depending on patient risk and past history of hospital-acquired Legionnaires’ disease.

Ice machines in a healthcare setting?

Should ice machines in a healthcare setting have bacteriological filters? If so, why?

Generally that decision is needed to be made on a facility/team level. We do not see the need for all healthcare facilities using point-of-use microbiological filters on all ice machines.
The important piece here is to understand the risk at the facility. There are a couple questions that you should consider:

  • Has the facility performed environmental sampling to determine if Legionella is present in the water system or present in ice machines?
  • If yes – has the facility responded to positive results and able to remediate the ice machines (cleaning/disinfecting and then follow up sampling to confirm efficacy)?
  • Does the facility have a water management plan that address routine testing, maintenance, and cleaning of the ice machines?
  • Is there a history of cases of Legionnaire’s disease at the facility?
  • Are there high risk patients using/exposed to any for the ice machines?

All of these questions are important to understand if you should use POU filters on the ice machines. We do know of facilities that have had no issues, yet still use the POU filters as an extra step in managing their facility. Its important to manage the ice machines and understand their risk before making these decisions.