Legionellosis is a potentially fatal infectious disease
Infectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...

 caused by gram negative, aerobic bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 belonging to the genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

Legionella is a pathogenic Gram negative bacterium, including species that cause legionellosis or Legionnaires' disease, most notably L. pneumophila. It may be readily visualized with a silver stain....

. Over 90% of legionellosis cases are caused by Legionella pneumophila
Legionella pneumophila
Legionella pneumophila is a thin, ærobic, pleomorphic, flagellated, non-spore forming, Gram-negative bacterium of the genus Legionella. L. pneumophila is the primary human pathogenic bacterium in this group and is the causative agent of legionellosis or Legionnaires' disease.-Characterization:L...

, a ubiquitous aquatic organism that thrives in temperatures between 25 and 45 °C (77 and 113 F), with an optimum temperature of 35 °C (95 °F).

Legionellosis takes two distinct forms:
  • Legionnaires' disease, also known as "Legion Fever", is the more severe form of the infection and produces high fever and pneumonia
    Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...

  • Pontiac fever is caused by the same bacteria but produces a milder respiratory illness without pneumonia that resembles acute
    Acute (medicine)
    In medicine, an acute disease is a disease with either or both of:# a rapid onset, as in acute infection# a short course ....

    Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...

    . Pontiac fever also has a spontaneous resolution.

Legionnaires' disease acquired its name in July 1976 when an outbreak
Outbreak is a term used in epidemiology to describe an occurrence of disease greater than would otherwise be expected at a particular time and place. It may affect a small and localized group or impact upon thousands of people across an entire continent. Two linked cases of a rare infectious...

 of pneumonia occurred among people attending a convention of the American Legion
American Legion
The American Legion is a mutual-aid organization of veterans of the United States armed forces chartered by the United States Congress. It was founded to benefit those veterans who served during a wartime period as defined by Congress...

 at the Bellevue-Stratford Hotel
The Bellevue-Stratford Hotel
The Bellevue is a landmark building at Broad & Walnut Streets in Center City, Philadelphia, Pennsylvania. It has continued as a well-known institution for more than a century. In the past 30 years the hotel has undergone minor name changes, but still is widely known by its historic name, The...

 in Philadelphia. On January 18, 1977 the causative agent was identified as a previously unknown strain of bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

, subsequently named Legionella. Some people can be infected with the Legionella bacteria and have only mild symptoms or no illness at all.

Outbreaks of Legionnaires' disease receive significant media attention. However, this disease usually occurs as single, isolated cases not associated with any recognized outbreak. When outbreaks do occur, they are usually in the summer and early autumn, though cases may occur at any time of year. The fatality rate of Legionnaires' disease has ranged from 5% to 30% during various outbreaks. "The death rate for patients who develop Legionnaire's disease while in the hospital is close to 50%, especially when antibiotics are started late," according to the NIH and U.S. National Library of Medicine service's MedlinePlus. Most infections occur in those who are middle-age or older.

Signs and symptoms

Patients with Legionnaires' disease usually have fever, chills, and a cough, which may be dry or may produce sputum
Sputum is mucus that is coughed up from the lower airways. It is usually used for microbiological investigations of respiratory infections....

. Some patients also have muscle aches, headache, tiredness, loss of appetite, loss of coordination (ataxia), and occasionally diarrhea and vomiting. Confusion and impaired cognition may also occur , as can a so-called 'relative bradycardia
Bradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...

', i.e. low or low normal heart rate despite the presence of a fever. Laboratory tests may show that patients’ renal functions, liver functions and electrolytes are deranged, including hyponatremia
Hyponatremia is an electrolyte disturbance in which the sodium concentration in the serum is lower than normal. In the vast majority of cases, hyponatremia occurs as a result of excess body water diluting the serum sodium and is not due to sodium deficiency. Sodium is the dominant extracellular...

. Chest X-rays often show pneumonia with bi-basal consolidation. It is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms or radiologic
Radiology is a medical specialty that employs the use of imaging to both diagnose and treat disease visualized within the human body. Radiologists use an array of imaging technologies to diagnose or treat diseases...

 findings alone; other tests are required for diagnosis.

Persons with Pontiac fever experience fever and muscle aches without pneumonia. They generally recover in 2 to 5 days without treatment.

The time between the patient's exposure to the bacterium and the onset of illness for Legionnaires' disease is 2 to 10 days; for Pontiac fever, it is shorter, generally a few hours to 2 days.


L. pneumophila is specifically considered as a pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

 of the respiratory tract
Respiratory tract
In humans the respiratory tract is the part of the anatomy involved with the process of respiration.The respiratory tract is divided into 3 segments:*Upper respiratory tract: nose and nasal passages, paranasal sinuses, and throat or pharynx...

. Surface organelles are made up from at least forty various protein components reconcile motile bacteria.. Other infections have also been reported, including haemodialysis fistulae, pericarditis
Pericarditis is an inflammation of the pericardium . A characteristic chest pain is often present.The causes of pericarditis are varied, including viral infections of the pericardium, idiopathic causes, uremic pericarditis, bacterial infections of the precardium Pericarditis is an inflammation of...

, and wound and skin infections. Bacteraemia is often associated with Legionnaires' disease. Intestinal infections may only occur as part of respiratory infections, and where gastrointestinal symptoms have on occasion been described.

One interesting feature in transmissive Legionella pneumophila is how monopolar flagellum is made up of the flagellin subunit FlaA. The function of the flagellum involves the development of Legionella pneumophila for "human macrophage-like cell lines and cytotoxicity to macrophages". Recent studies have shown flagellin noticed by mouse macrophages bring about cell death by the activation of cytosolic Naip5 (Birc1e) receptor..

According to the Centers for Disease Control and Prevention laboratory, antisera produced in rabbits have been prepared against all species and serogroups of Legionella and have been used in the CDC laboratory to distinguish the most Legionella strains in slide agglutination test. Although, the development of an antigen that can diagnose infections with all species and serogroups of Legionella has not yet been discovered. .

Infections of protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...

 such as Hartmannella vermiformis and related protozoa have been shown to be able to support the growth of L. pneumophila in tap water. Also Acanthamoeba
Acanthamoeba is a genus of amoebae, one of the most common protozoa in soil, and also frequently found in fresh water and other habitats. The cells are small, usually 15 to 35 μm in length and oval to triangular in shape when moving. The pseudopods form a clear hemispherical lobe at the anterior,...

, Naegleria
Naegleria is a eukaryotic genus. The genus was named after French zoologist Mathieu Naegler.Species include:* Naegleria fowleri, which causes a rare and generally fatal disease in humans* Naegleria gruberi-External links:...

and Tetrahymena
Tetrahymena are free-living ciliate protozoa that can also switch from commensalistic to pathogenic modes of survival. They are common in fresh-water. Tetrahymena species used as model organisms in biomedical research are T. thermophila and T. pyriformis.- T...

can be infected by L. pneumophila. This pathway may be how these organisms survive in the environment.


Infection normally occurs after inhaling an aerosol
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...

 (fine airborn particles) containing Legionella bacteria. Such particles could originate from any infected water source. When mechanical action breaks the surface of the water, small water droplets are formed, which evaporate very quickly. If these droplets contain bacteria, the bacteria cells remain suspended in the air, invisible to the naked eye and small enough to be inhaled into the lungs. This often occurs in poorly ventilated areas such as prisons where a condensating air conditioner can spread it throughout the entire room, infecting anyone not immune to the strain of bacteria.

Potential sources of such contaminated water include cooling towers (some 40% to 60% of ones tested) used in industrial cooling water systems as well as in large central air conditioning systems, evaporative coolers, nebulizers, humidifiers, whirlpools, hot water systems
Water heating
Water heating is a thermodynamic process using an energy source to heat water above its initial temperature. Typical domestic uses of hot water are for cooking, cleaning, bathing, and space heating...

, shower
A shower is an area in which one bathes underneath a spray of water.- History :...

s, windshield washers, whirlpool spas
Jacuzzi is a company that produces whirlpool bathtubs and spas. Its first product was a bath with massaging jets. The term "jacuzzi" is now often used generically to refer to any bathtub with massaging jets.-History:...

, architectural fountains
A fountain is a piece of architecture which pours water into a basin or jets it into the air either to supply drinking water or for decorative or dramatic effect....

, room-air humidifiers
A humidifier is a household appliance that increases humidity in a single room or in the entire house. There are point-of-use humidifiers, which are commonly used to humidify a single room, and whole-house or furnace humidifiers, which connect to a home's HVAC system to provide humidity to the...

, ice making machines
An ice maker, ice generator,or ice machine may refer to either a consumer device for making ice, found inside a home freezer; a stand-alone appliance for making ice, or an industrial machine for making ice on a large scale...

, misting equipment, and similar disseminators that draw upon a public water supply.

The disease may also be transmitted from contaminated aerosols generated in hot tubs if the disinfection and maintenance program is not done rigorously. Freshwater ponds, creeks, and ornamental fountains are potential sources of Legionella. The disease is particularly associated with hotels, fountains, cruise ship
Cruise ship
A cruise ship or cruise liner is a passenger ship used for pleasure voyages, where the voyage itself and the ship's amenities are part of the experience, as well as the different destinations along the way...

s and hospitals with complex potable water systems and cooling systems.

The development of bacterial infections may cause Legionnaires’ disease. Respiratory care devices such as humidifiers and nebulizers used with contaminated tap water may contain Legionella. Using sterile water is very important, especially when using respiratory care devices. .


A recent research study provided evidence that Legionella pneumophila, the causative agent of Legionnaires' disease, can travel airborne at least 6 km from its source.In 2000, ASHRAE issued guidelines to maintain water systems and the decrease the chances of Legionnaires’ disease transmission. The guidelines were not valued because legionellae multiple in such temperatures. On the other hand, a lot of states had regulations that limited temperatures in health care facilities in order to reduce scalding injuries.. It was previously believed that transmission of the bacterium was restricted to much shorter distances. A team of French scientists reviewed the details of an epidemic of Legionnaires' disease that took place in Pas-de-Calais in northern France in 2003–2004. There were 86 confirmed cases during the outbreak, of whom 18 died. The source of infection was identified as a cooling tower in a petrochemical
Petrochemicals are chemical products derived from petroleum. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as corn or sugar cane....

 plant, and an analysis of those affected in the outbreak revealed that some infected people lived as far as 6–7 km from the plant.

A study of Legionnaires' disease cases in May 2005 in Sarpsborg
is a city and municipality in Østfold county, Norway. The administrative centre of the municipality is the city of Sarpsborg.Sarpsborg is part of the fifth largest urban area in Norway when paired with neighbouring Fredrikstad...

, Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

 concluded that: "The high velocity, large drift, and high humidity in the air scrubber may have contributed to the wide spread of Legionella species, probably for >10 km. "...

In 2010 a study by the UK Health Protection Agency
Health Protection Agency
The Health Protection Agency, or, in Welsh, Yr Asiantaeth Diogelu Iechyd is a statutory corporation. It is an independent UK organisation that was set up by the government in 2003 to protect the public from threats to their health from infectious diseases and environmental hazards...

 reported that 20% of cases may be caused by infected windscreen washer systems filled with pure water. The finding came after researchers spotted that professional drivers are five times more likely to contract the disease. No cases of infected systems were found whenever a suitable washer fluid
Windshield washer fluid
Windshield washer fluid is a fluid for motor vehicles that is used in cleaning the windshield with the windshield wiper while the vehicle is being driven.-Delivery system:A control within the car can be operated to squirt fluid onto the windshield, typically using an...

 was used.

Temperature affects the survival of Legionella as follows:

Disinfection range
  • At 66 °C (150.8 °F): Legionellae die within 2 minutes
  • At 60 °C (140 °F): They die within 32 minutes
  • At 55 °C (131 °F): They die within 5 to 6 hours
  • Above 50 °C (122 °F): They can survive but do not multiply: Ideal growth range: Growth range
  • Below 20 °C (68 °F): They can survive but are dormant

Removing slime
A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance...

, which can carry legionellae when airborne, may be an effective control process.

Action levels

The European Working Group for Legionella Infections
European Working Group for Legionella Infections
The European Working Group for Legionella Infections was formed in 1986. Its members are scientists with an interest in improving knowledge and information on the epidemiological and microbiological aspects of legionnaires' disease...

 (EWGLI) was established in 1986 within the European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

 framework to share knowledge and experience about potential sources of Legionella and their control. This group has published guidelines about the actions to be taken to limit the number of colony forming units (i.e., the "aerobic count") of micro-organisms per mL at 30 °C (minimum 48 hours incubation):
Aerobic count Legionella Action required
10,000 or less 1,000 or less System under control.
more than 10,000
up to 100,000
more than 1,000
up to 10,000
Review program operation. The count should be confirmed by immediate re-sampling. If a similar count is found again, a review of the control measures and risk assessment should be carried out to identify any remedial actions.
more than 100,000 more than 10,000 Implement corrective action. The system should immediately be re-sampled. It should then be ‘shot dosed’ with an appropriate biocide, as a precaution. The risk assessment and control measures should be reviewed to identify remedial actions.

Almost all natural water sources contain Legionella and their presence should not be taken as an indication of a problem. The tabled figures are for total aerobic plate count, cfu/ml at 30 °C (minimum 48 hours incubation) with colony count determined by the pour plate method according to ISO 6222(21) or spread plate method on yeast extract agar. Legionella isolation can be conducted using the method developed by the US Center for Disease Control using buffered charcoal yeast extract agar with antibiotics.

Many other governmental agencies, cooling tower manufacturers, and industrial trade organizations have developed design and maintenance guidelines for preventing or controlling the growth of Legionella in cooling towers. However, in the US, there are no regulations requiring testing or maintaining any specified levels in these facilities.

Breeding ground

The bacteria grow best in warm water, like the kind found in hot tubs, cooling towers, hot water tanks, large plumbing systems, or parts of the air-conditioning systems of large buildings. Indoor ornamental fountains have been confirmed as a cause of Legionnaires' disease outbreaks, in which submerged lighting as a heat source was attributed to the outbreak in all documented cases. Controlling the growth of Legionella in ornamental fountains is touched on in many of the listed guidelines. However, specific guidelines for ornamental fountains have also been published.

Adding an antibacterial agent to the automobiles' windshield system's reservoir is also recommended. Legionellae have been discovered in up to 40% of freshwater environments
and have been in up to 80% of freshwater sites by PCR hybridization assay. .

Regulations and ordinances

The guidance issued by the UK government's Health and Safety Executive (HSE) now recommends that microbiological monitoring for wet cooling systems, using a dipslide
Dipslides are in general a test for the presence of bacteria within fluids / solids or on surfaces. They are incredibly useful tools in identifying any potentially damaging organisms that may be present and breeding within the home or workplace....

, should be performed weekly. The guidance now also recommends that routine testing for legionella bacteria in wet cooling systems be carried out at least quarterly, and more frequently when a system is being commissioned, or if the bacteria has been identified on a previous occasion.

The City of Garland, Texas
Garland, Texas
-Climate:* The average warmest month is July.* The highest recorded temperature was in 2000.* On average, the coolest month is January.* The lowest recorded temperature was in 1989.* The maximum average precipitation occurs in May....

 requires yearly testing for legionella bacteria at cooling towers at apartment buildings.

Malta , officially known as the Republic of Malta , is a Southern European country consisting of an archipelago situated in the centre of the Mediterranean, south of Sicily, east of Tunisia and north of Libya, with Gibraltar to the west and Alexandria to the east.Malta covers just over in...

 requires twice yearly testing for Legionella bacteria at cooling towers and water fountains. Malta
Malta , officially known as the Republic of Malta , is a Southern European country consisting of an archipelago situated in the centre of the Mediterranean, south of Sicily, east of Tunisia and north of Libya, with Gibraltar to the west and Alexandria to the east.Malta covers just over in...

 prohibits the installation of new cooling towers and evaporative condensers at health care facilities and schools.

The Texas Department of State Health Services has provided guidelines for hospitals to detect and prevent the spread of nosocomial infection
Nosocomial infection
A nosocomial infection , also known as a hospital-acquired infection or HAI, is an infection whose development is favoured by a hospital environment, such as one acquired by a patient during a hospital visit or one developing among hospital staff...

 due to legionella.

Limiting growth

Legionella bacteria themselves can be inactivated by UV
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 light. However, Legionella bacteria that grow and reproduce in amoeba
Amoeba is a genus of Protozoa.History=The amoeba was first discovered by August Johann Rösel von Rosenhof in 1757. Early naturalists referred to Amoeba as the Proteus animalcule after the Greek god Proteus, who could change his shape...

e or that are sheltered in corrosion particles cannot be killed by UV light alone. An innovative way is the combination of ultrasonics
Ultrasonics is a term meaning the application of ultrasound. It is often used in industry as a shorthand term for any equipment employing ultrasonic principles....

 and UVC light. This uses a two-stage process, where ultrasonic cavitation
Cavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...

 disrupts the amoebae or corrosion particles and leaves the Legionella bacteria exposed for UV radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...

. Such combined system are used for example in hot water systems in sensitive areas, such as hospitals, where the inhabitants are more vulnerable than in normal environments.Legionellae thrives in moist soil and environments as “intracellular parasites of free-living protozoa”. Molds, protozoa and mammalian cells are all various hosts that Legionellae can still infect. . .

Legionella will grow in water at temperatures from 20 to 50 °C (68 to 122 F). However, the bacteria reproduce at the greatest rate in stagnant water at temperatures of 35 to 46 °C (95 to 114.8 F).

Legionella longbeachae
Legionella longbeachae
Legionella longbeachae is one species of the family Legionellaceae. It was first isolated from a patient in Long Beach, California. It is found predominantly in soil and potting compost. In humans, the infection is sometimes called Pontiac Fever. Human infection from L...

, an organism in the Legionella family, is found in soils and compost
Compost is organic matter that has been decomposed and recycled as a fertilizer and soil amendment. Compost is a key ingredient in organic farming. At its most essential, the process of composting requires simply piling up waste outdoors and waiting for the materials to break down from anywhere...

. Thus, the dust from purchased bags of soil, compost, or potting mix is a potential source of Legionella.

The first L. longbeachae cases of infection involving potting soil were reported in the United States in 2000..


People of any age may suffer from Legionnaires' disease, but the illness most often affects middle-age and older persons, particularly those who smoke cigarettes or have chronic lung disease
Chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease , also known as chronic obstructive lung disease , chronic obstructive airway disease , chronic airflow limitation and chronic obstructive respiratory disease , is the co-occurrence of chronic bronchitis and emphysema, a pair of commonly co-existing diseases...

. Immunocompromised
Immunodeficiency is a state in which the immune system's ability to fight infectious disease is compromised or entirely absent. Immunodeficiency may also decrease cancer immunosurveillance. Most cases of immunodeficiency are acquired but some people are born with defects in their immune system,...

 patients are also at elevated risk. Pontiac fever most commonly occurs in persons who are otherwise healthy.

The most useful diagnostic tests detect the bacteria in sputum, find Legionella antigens in urine samples (due to renal fibrosis), or the comparison of Legionella antibody levels in two blood samples taken 3 to 6 weeks apart. A urine antigen test which is simple, quick, and very reliable will only detect Legionella pneumophila serogroup 1, which accounts for 70% of disease cause by L. pneumophila. This test was developed by Richard Kohler and described in the Journal of Infectious disease in 1982 while Dr. Kohler was a junior faculty member at the Indiana University School of medicine . In addition the urine antigen test will not identify the specific subtypes; so it cannot be used to match the patient with the environmental source of infection. Legionella can be isolated on a CYE agar as well.


Current treatments of choice are the respiratory tract quinolones (levofloxacin
Levofloxacin is a synthetic chemotherapeutic antibiotic of the fluoroquinolone drug class and is used to treat severe or life-threatening bacterial infections or bacterial infections that have failed to respond to other antibiotic classes. It is sold under various brand names, such as Levaquin and...

, moxifloxacin
Moxifloxacin is a fourth-generation synthetic fluoroquinolone antibacterial agent developed by Bayer AG . It is marketed worldwide under the brand names Avelox, Avalox, and Avelon for oral treatment. In most countries, the drug is also available in parenteral form for intravenous infusion...

, gemifloxacin
Gemifloxacin mesylate is an oral broad-spectrum quinolone antibacterial agent used in the treatment of acute bacterial exacerbation of chronic bronchitis and mild-to-moderate pneumonia....

) or newer macrolides (azithromycin
Azithromycin is an azalide, a subclass of macrolide antibiotics. Azithromycin is one of the world's best-selling antibiotics...

, clarithromycin
Clarithromycin is a macrolide antibiotic used to treat pharyngitis, tonsillitis, acute maxillary sinusitis, acute bacterial exacerbation of chronic bronchitis, pneumonia , skin and skin structure infections...

, roxithromycin
Roxithromycin is a semi-synthetic macrolide antibiotic. It is used to treat respiratory tract, urinary and soft tissue infections. Roxithromycin is derived from erythromycin, containing the same 14-membered lactone ring. However, an N-oxime side chain is attached to the lactone ring...

). The antibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...

s used most frequently have been levofloxacin and azithromycin. Macrolides are used in all age groups while tetracyclines are prescribed for children above the age of 12 and quinolones above the age of 18. Rifampicin
Rifampicin or rifampin is a bactericidal antibiotic drug of the rifamycin group. It is a semisynthetic compound derived from Amycolatopsis rifamycinica ...

 can be used in combination with a quinolone or macrolide. It is uncertain whether rifampicin is an effective antibiotic to take for treatment.The Infectious Diseases Society of America does not recommend the usage of rifampicin with added regimens. Tetracyclines and erythromycin
Erythromycin is a macrolide antibiotic that has an antimicrobial spectrum similar to or slightly wider than that of penicillin, and is often used for people who have an allergy to penicillins. For respiratory tract infections, it has better coverage of atypical organisms, including mycoplasma and...

 led to improved outcomes compared to other antibiotics in the original American Legion outbreak. These antibiotics are effective because they have excellent intracellular penetration and Legionella infects cells.

The mortality at the original American Legion convention in 1976 was high (34 deaths in 180 infected individuals) because the antibiotics used (including penicillin
Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V....

s, cephalosporin
The cephalosporins are a class of β-lactam antibiotics originally derived from Acremonium, which was previously known as "Cephalosporium".Together with cephamycins they constitute a subgroup of β-lactam antibiotics called cephems.-Medical use:...

s, and aminoglycoside
An aminoglycoside is a molecule or a portion of a molecule composed of amino-modifiedsugars.Several aminoglycosides function as antibiotics that are effective against certain types of bacteria...

s) had poor intracellular penetration. Mortality has plunged to less than 5% if therapy is started quickly. Delay in giving the appropriate antibiotic leads to higher mortality.


According to the journal Infection Control and Hospital Epidemiology, hospital-acquired Legionella pneumonia has a fatality rate of 28%, and the principal source of infection in such cases is the drinking-water distribution system.


There are about 8,000 to 18,000 cases of Legionnaires’ disease each year in the United States, according to the Bureau of Communicable Disease Control. Much has been learned about the epidemiology of Legionnaires' disease since the organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

 was first identified in 1976. National surveillance systems and research studies were established early, and in recent years improved ascertainment and changes in clinical methods of diagnosis have contributed to an upsurge in reported cases in many countries. Environmental studies continue to identify novel sources of infection, leading to regular revisions of guidelines and regulations. Between 1995 and 2005 over 32,000 cases of Legionnaires' disease and more than 600 outbreaks were reported to the European Working Group for Legionella Infections
European Working Group for Legionella Infections
The European Working Group for Legionella Infections was formed in 1986. Its members are scientists with an interest in improving knowledge and information on the epidemiological and microbiological aspects of legionnaires' disease...

 (EWGLI). In the future, there may be an increase in cases as the population becomes more elderly. There is a shortage of data on Legionella in developing countries and it is likely that Legionella-related illness is underdiagnosed worldwide. Improvements in diagnosis and surveillance in developing countries would be expected to reveal far higher levels of morbidity and mortality than are currently recognised. Similarly, improved diagnosis of human illness related to legionella species and serogroups other than legionella pneumophila would improve knowledge about their incidence and spread.


Year City Venue SourceCases Deaths Notes
1976 Philadelphia, Pennsylvania
Philadelphia, Pennsylvania
Philadelphia is the largest city in the Commonwealth of Pennsylvania and the county seat of Philadelphia County, with which it is coterminous. The city is located in the Northeastern United States along the Delaware and Schuylkill rivers. It is the fifth-most-populous city in the United States,...

1976 Philadelphia Legionellosis outbreak
1976 Philadelphia legionellosis outbreak
The 1976 Philadelphia legionellosis outbreak was the first recognized outbreak of legionellosis.-History:It occurred on July 27, 1976 at the Bellevue Stratford Hotel in Philadelphia, Pennsylvania, where members of the American Legion, a United States military veterans association, had gathered for...

air conditioning
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...

221 This was the eponymous outbreak and the deadliest.
1999 Bovenkarspel, Netherlands humidifier 200 In March 1999, an outbreak in the Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

 occurred during a flower exhibition in Bovenkarspel
Bovenkarspel is a town in the Netherlands, in the province of North Holland. Until 1979, it was a separate municipality.-Legionella outbreak:...

. 200 people became ill and at least 32 people died. There is a possibility that more people died from it, but these people were buried before the Legionella infection was recognized. The source of the bacteria were probably a whirlpool
A whirlpool is a swirling body of water usually produced by ocean tides. The vast majority of whirlpools are not very powerful. More powerful ones are more properly termed maelstroms. Vortex is the proper term for any whirlpool that has a downdraft...

 and a humidifier
A humidifier is a household appliance that increases humidity in a single room or in the entire house. There are point-of-use humidifiers, which are commonly used to humidify a single room, and whole-house or furnace humidifiers, which connect to a home's HVAC system to provide humidity to the...

 in the exhibition area.
1985 Stafford, England  air conditioning
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...

175 In April 1985, 175 patients were admitted to the District or Kingsmead Stafford
Stafford is the county town of Staffordshire, in the West Midlands region of England. It lies approximately north of Wolverhampton and south of Stoke-on-Trent, adjacent to the M6 motorway Junction 13 to Junction 14...

 Hospitals with chest infection or pneumonia. A total of 28 people died. Medical diagnosis showed that Legionnaires' disease was responsible and the immediate epidemiological investigation traced the source of the infection to the air-conditioning cooling tower on the roof of Stafford District Hospital. A Government Inquiry was convened to investigate how the infection occurred and why it became Britain's largest epidemic of Legionnaires' disease. The infection was linked to one small zone in the hospital: the outpatients department. The initial investigation searched for engineering reasons to explain why this particular zone was the risk area. More detailed and wider epidemiological surveys subsequently showed that staff working in the whole area supplied with fresh air taken adjacent to the tower, had antibodies to the disease. The outpatients department was unique in having a very large transient population of susceptible individuals either receiving treatment or accompanying friends.
2005 Toronto, Canada 
2005 Fredrikstad, Norway  56 people became ill and ten died from Legionnaires' disease caused by bacteria growing in an air scrubber of a nearby factory.
2002 Barrow-in-Furness
Barrow-in-Furness is an industrial town and seaport which forms about half the territory of the wider Borough of Barrow-in-Furness in the county of Cumbria, England. It lies north of Liverpool, northwest of Manchester and southwest from the county town of Carlisle...

2002 Barrow-in-Furness Legionellosis outbreak  air conditioning
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...

In 2002, Barrow-in-Furness
Barrow-in-Furness is an industrial town and seaport which forms about half the territory of the wider Borough of Barrow-in-Furness in the county of Cumbria, England. It lies north of Liverpool, northwest of Manchester and southwest from the county town of Carlisle...

 in the U.K.
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 suffered an outbreak of Legionnaires' disease. Six women and one man died as a result of the illness; another 172 people also contracted the disease. The cause was found to be a contaminated cooling tower at the town’s Forum 28
Forum 28
The Forum 28 is a media and arts centre located in the British town of Barrow-in-Furness. The site is currently home to a large theatre and stage, several conference and function rooms, Barrow's main tourist information centre and a Costa Coffee outlet...

 arts centre. Barrow Borough Council
Barrow-in-Furness (borough)
Barrow-in-Furness is a local government district with borough status in Cumbria, England. It is named after its main town, Barrow-in-Furness. Other settlements include Dalton-in-Furness, Roose and Askam-in-Furness. It is the smallest borough in the county, but is the most densely populated, with...

 later became the first public body in the UK to be charged with corporate manslaughter
Corporate manslaughter
Corporate manslaughter is a criminal offence in English law, being an act of homicide committed by a company or organisation. In general, in English criminal law, a juristic person is in the same position as a natural person, and may be convicted for committing many offences...

 but were cleared. They were, however, along with architect
An architect is a person trained in the planning, design and oversight of the construction of buildings. To practice architecture means to offer or render services in connection with the design and construction of a building, or group of buildings and the space within the site surrounding the...

 Gillian Beckingham, fined for breaches of Health and Safety regulations in a trial that ended in 2006.
2001 Murcia, Spain  hospital The world’s largest outbreak of Legionnaires' disease happened in July 2001 with patients appearing at the hospital on July 7, in Murcia
-History:It is widely believed that Murcia's name is derived from the Latin words of Myrtea or Murtea, meaning land of Myrtle , although it may also be a derivation of the word Murtia, which would mean Murtius Village...

, Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

. More than 800 suspected cases were recorded by the time the last case was treated on July 22; 636–696 of these cases were estimated and 449 confirmed (so, at least 16,000 people were exposed to the bacterium) and 6 died . A case-fatality rate
Case fatality
In epidemiology, case fatality or fatality rate, is the ratio of deaths within a designated population of people with a particular condition, over a certain period of time. An example of a fatality rate would be 9 deaths per 10,000 people at risk per year...

 of approximately 1%.
2008 New Brunswick, New Jersey
New Brunswick, New Jersey
New Brunswick is a city in Middlesex County, New Jersey, USA. It is the county seat and the home of Rutgers University. The city is located on the Northeast Corridor rail line, southwest of Manhattan, on the southern bank of the Raritan River. At the 2010 United States Census, the population of...

Saint Peter's University Hospital
Saint Peter's University Hospital
Saint Peter's University Hospital is a Roman Catholic hospital on Easton Avenue in New Brunswick, New Jersey. The hospital is a member of the Saint Peter's Healthcare System, Inc. a New Jersey nonprofit corporation sponsored by the Roman Catholic Diocese of Metuchen.-Overview:Saint Peter's...

drinking water Chlorination
Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water...

 in the water system had dropped below effective levels.

Melbourne, Australia, 2000

In April 2000, an outbreak of Legionella pnemophila serogroup 1 occurred in Melbourne, Australia. The outbreak resulted in 125 confirmed cases of Legionnaire's disease, with 95 (76%) hospitalised. It is reported that 4 died from the outbreak. The investigation traced the source of the infection to the cooling tower at the newly opened aquarium. Since this outbreak, legionella infection statistics are required to be reported by the state government as a notifiable disease. Stringent Regulations were introduced by the State to control legionella in 2001.

Los Angeles, United States, 2011

In Los Angeles, CA, bacteria that causes Legionnaires' disease was found in a hot tub at the Playboy Mansion
Playboy Mansion
The Playboy Mansion is the home of Playboy magazine founder Hugh Hefner. Located in the Holmby Hills area of Los Angeles, California, the mansion became famous during the 1970s through media reports of Hefner's lavish parties.-History:The house is described as being in the "Gothic-Tudor" style...

where scores of people became ill after attending a fundraiser in February. Officials contacted 439 people and found that 123 had fevers and at least one other symptom with 69 falling ill on the same day.
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