How Many Legionella Species Exist & Which Ones Cause Legionnaires’ Disease?

How Many Legionella Species Exist?

While there are more than 50 different recognised Legionella species, less than half of those can cause illness in humans. However, while around 20 species are known to be harmful to us, just one has been identified as the cause of most outbreaks of Legionnaires’ disease.

Here we review the different strains of Legionella bacteria that have been identified to date and pick out those that have been linked to disease.

Legionella pneumophila species

Legionella pneumophila species serogroup 1, 3, 4 and 6 have been linked to disease in humans with L. pneumophila serogroup 1 being the most serious and responsible for the majority of infections. As the name suggests, it can cause pneumonia along with sickness and diarrhoea. While other species of the bacteria can lead to illness, Legionella pneumophila has claimed a fatality rate of around 10%.

We know those at greatest risk include people whose immune systems are suppressed, those who are elderly, and those who have long-term illnesses, particularly of the respiratory system.

Different species of the bacteria are responsible for causing Pontiac fever

The condition Pontiac fever is not as well known as Legionnaires’ disease. It is typically caused by two strains of Legionella bacteria – Legionella feeleii and Legionella longbeachae. Pontiac fever is not always diagnosed accurately but is not as serious as Legionnaires’ disease. Those unfortunate enough to become infected may assume they have the ‘flu, since the symptoms are very similar in nature.

Other strains of legionella may cause pneumonia

All forms of Legionella bacteria can be inhaled via water spray or droplets (an aerosol) if the circumstances allow for it. A handful of Legionella species, including Legionella dumoffi and Legionella bozemanae, can trigger cases of pneumonia in people who become exposed to the bacteria.

Control techniques must cover all Legionella species

Outbreaks of Legionnaires’ disease and Pontiac fever can occur if water systems are not managed correctly and become contaminated with the bacteria. If you own or manage a building or facility containing water systems or processes that use water, you must ensure proper measures are put in place to minimise the dangers from all species of Legionella bacteria. Typical measures include identifying and assessing the risks (with a legionella risk assessment), developing a programme to control those risks, managing the effectiveness of the steps taken and appointing a responsible person to manage the process.

Keeping systems clean, minimising dead legs, treating the water, and monitoring water temperatures will all contribute to the safe management of a water system. Minimising any water spray is imperative, since the bacteria must be present in a mist or spray that can be inhaled to pose a risk to those nearby. Water temperatures should either be below 20 degrees Celsius (at cold water outlets) or higher than 50 degrees Celsius (at hot water outlets, 55 oC in healthcare). Legionella will multiply quickly if allowed to do so in warm water. Regular testing of the water temperatures should help to control levels of bacteria, keeping them at acceptably low levels.

While not all Legionella species are harmful to humans, it is vital to ensure you assess all water systems for risk and treat them accordingly.

Known Legionella species

The following table lists identified Legionella species, sero group details and their ability to cause human infection.

Legionella SpeciesSerogroupHuman InfectionInformation
L. adelaidensisNoA Legionella-like organism (strain 1762-AUS-E) was isolated from a cooling tower of an air-conditioning system in Adelaide, South Australia, Australia.
L. anisaYesPleural infection caused by Legionella anisa.
L. beliardensisNoLegionella gresilensis sp. nov. and Legionella beliardensis sp. nov., isolated from water in France.
L. birminghamensisYesLegionella birminghamensis sp. nov. isolated from a cardiac transplant recipient.
L. bozemanii1Yes Pneumonia caused by Legionella bozemanii and acquired by a 75-year-old man while on holiday in Majorca. This appears to be the first report of such a case from Europe.
L. bozemanii2YesLegionella bozemanii serogroup 2: a new etiological agent.
L. brunensisNoLegionella moravica sp. nov. and Legionella brunensis sp. nov. isolated from cooling-tower water.
L. busanensisNoLegionella busanensis sp. nov., isolated from cooling tower water in Korea.
L. cardiacaYesLegionella cardiaca sp. nov., isolated from a case of native valve endocarditis in a human heart.
L. cherriiYesDisease due to the Legionellaceae (other than Legionella pneumophila). Historical, microbiological, clinical, and epidemiological review.
L. cincinnatiensisYesLegionella cincinnatiensis sp. nov. isolated from a patient with pneumonia.
L. clemsonensisYesLegionella clemsonensis sp. nov.: a green fluorescing Legionella strain from a patient with pneumonia.
L. donaldsoniiNoLegionella prevalence in wastewater treatment plants of Taiwan.
L. drancourtiiNoLegionella drancourtii sp. nov., a strictly intracellular amoebal pathogen.
L. dresdenensisNoLegionella dresdenensis sp. nov., isolated from river water.
L. drozanskiiNoLegionella drozanskii sp. nov., Legionella rowbothamii sp. nov. and Legionella fallonii sp. nov.: three unusual new Legionella species.
L. dumoffiiYesLegionnaires’ disease caused by Legionella dumoffii in distilled water.
L. erythraNoLipopolysaccharides of Legionella erythra and Legionella oakridgensis.
L. fairfieldensisNoLegionella fairfieldensis sp. nov. isolated from cooling tower waters in Australia.
L. falloniiNoLegionella drozanskii sp. nov., Legionella rowbothamii sp. nov. and Legionella fallonii sp. nov.: three unusual new Legionella species.
L. feeleii1YesLegionella feeleii-associated pneumonia in humans.
L. feeleii2YesSecond serogroup of Legionella feeleii strains isolated from humans.
L. geestianaNoFive new Legionella species isolated from water.
L. genomospecies 1NoLegionella waltersii sp. nov. and an unnamed Legionella genomospecies isolated from water in Australia.
L. gormaniiYesFirst isolation of Legionella gormanii from human disease.
L. gratianaNoLegionella gratiana sp. nov. isolated from French spa water.
L. gresilensisNoLegionella gresilensis sp. nov. and Legionella beliardensis sp. nov., isolated from water in France.
L. hackeliae1YesTen new species of Legionella.
L. hackeliae2YesSecond serogroup of Legionella hackeliae isolated from a patient with pneumonia.
L. impletisoliNoLegionella impletisoli sp. nov. and Legionella yabuuchiae sp. nov., isolated from soils contaminated with industrial wastes in Japan.
L. israelensisNoSeasonal distribution of legionellae isolated from various types of water in Israel.
L. jamestowniensisNoInfection of macrophage-like cells by Legionella species that have not been associated with disease.
Candidatus L. jeoniiNoPhylogenetic characterization of Legionella-like endosymbiotic X-bacteria in Amoeba proteus: a proposal for ‘Candidatus Legionella jeonii’ sp. nov.
L. jordanisYesAortic valve endocarditis associated with Legionella infection after Mycoplasma pneumonia.
L. lansingensisYesLegionella lansingensis sp. nov. isolated from a patient with pneumonia and underlying chronic lymphocytic leukemia.
L. londiniensisNoFive new Legionella species isolated from water.
L. longbeachae1YesLegionella longbeachae species nova, another etiologic agent of human pneumonia.
L. longbeachae2YesRecognition of a second serogroup of Legionella longbeachae.
L. lyticaNoLegionella-like and other amoebal pathogens as agents of community-acquired pneumonia.
L. maceacherniiYesFatal Legionella maceachernii pneumonia.
L. massiliensisNoLegionella tunisiensis sp. nov. and Legionella massiliensis sp. nov., isolated from environmental water samples.
L. micdadeiYesOpportunistic lung infection due to “Pittsburgh Pneumonia Agent”.
L. moravicaNoLegionella moravica sp. nov. and Legionella brunensis sp. nov. isolated from cooling-tower water.
L. nagasakii/nagasakiensisNoLegionella nagasakiensis sp. nov., isolated from water samples and from a patient with pneumonia.
L. nautarumNoFive new Legionella species isolated from water.
L. norrlandicaNoFive new Legionella species isolated from water.
L. oakridgensisYesLegionella oakridgensis: laboratory diagnosis of a human infection.
L. parisiensisYesThe first clinical isolate of Legionella parisiensis, from a liver transplant patient with pneumonia.
Legionella pneumophila (Philadelphia 1)1YesClassification of the Legionnaires’ disease bacterium: Legionella pneumophila, genus novum, species nova, of the family Legionellaceae, familia nova.
L. pneumophila (Knoxville 1)1YesLegionellae isolated from clinical and environmental samples in Spain (1983-90): monoclonal typing of Legionella pneumophila serogroup 1 isolates.
L. pneumophila (Benidorm 030 E)1YesOutbreak of Legionnaires’ disease at University Hospital, Nottingham. Epidemiology, microbiology and control.
L. pneumophila (France 5811)1YesEvaluation of different primers for DNA fingerprinting of Legionella pneumophila serogroup 1 strains by polymerase chain reaction.
L. pneumophila (Allentown 1)1YesLegionellae isolated from clinical and environmental samples in Spain (1983-90): monoclonal typing of Legionella pneumophila serogroup 1 isolates.
L. pneumophila (OLDA)1YesLegionella pneumophila serogroup 1 population in Italy by monoclonal subtyping.
L. pneumophila (Oxford 4032 E)1YesEpidemiological studies using monoclonal antibodies to Legionella pneumophila serogroup 1.
L. pneumophila (Bellingham)1YesLegionella pneumophila serogroup 1 population in Italy by monoclonal subtyping.
L. pneumophila (Heysham 1)1YesDevelopment of a standardized subgrouping scheme for Legionella pneumophila serogroup 1 using monoclonal antibodies.
L. pneumophila (Camperdown 1)1YesLegionella pneumophila serogroup 1 population in Italy by monoclonal subtyping.
L. pneumophila (Togus 1)2YesRecognition of a new serogroup of Legionnaires disease bacterium.
L. pneumophila (Bloomington 2)3YesFatal pneumonia caused by Legionella pneumophila, serogroup 3: demonstration of the bacilli in extrathoracic organs.
L. pneumophila (Los Angeles)4YesPyelonephritis associated with Legionella pneumophila, serogroup 4.
L. pneumophila (Portland1)4YesLegionella pneumophila serogroup Lansing 3 isolated from a patient with fatal pneumonia, and descriptions of L. pneumophila subsp. pneumophila subsp. nov., L. pneumophila subsp. fraseri subsp. nov., and L. pneumophila subsp. pascullei subsp. nov.
L. pneumophila (Dallas 1E)5YesSerological and genotypic diversity among serogroup 5- reacting environmental Legionella isolates.
L. pneumophila (Cambridge 1)5YesLegionella pneumophila: monoclonal antibody typing of clinical and environmental isolates.
L. pneumophila (Chicago 1)6YesLegionella pneumophila serogroup six: isolation from cases of legionellosis, identification by immunofluorescence staining, and immunological response to infection.
L. pneumophila (Chicago 8)7YesIsolation and characterization of a seventh serogroup of Legionella pneumophila.
L. pneumophila (Concord 3)8YesNew serogroup of Legionella pneumophila, serogroup 8.
L. pneumophila (IN-23-G1-C2)9YesLegionella pneumophila serogroup 9: a cause of human pneumonia.
L. pneumophila (Leiden 1)10YesWater-related nosocomial pneumonia caused by Legionella pneumophila serogroups 1 and 10.
L. pneumophila (797-PA-H)11Yes11th serogroup of Legionella pneumophila isolated from a patient with fatal pneumonia.
L. pneumophila (570-CO-H)12YesLegionella pneumophila serogroup 12 isolated from human and environmental sources.
L. pneumophila (82A3105)13YesThirteenth serogroup of Legionella pneumophila isolated from patients with pneumonia.
L. pneumophila (1169-MN-H)14YesLegionella pneumophila serogroup 14 isolated from patients with fatal pneumonia.
L. pneumophila (Lansing 3)15YesLegionella pneumophila serogroup Lansing 3 isolated from a patient with fatal pneumonia, and descriptions of L. pneumophila subsp. pneumophila subsp. nov., L. pneumophila subsp. fraseri subsp. nov., and L. pneumophila subsp. pascullei subsp. nov.
L. quateirensisNoFive new Legionella species isolated from water.
L. quinlivanii1NoFive new Legionella species isolated from water.
L. quinlivanii2NoSecond serogroup of Legionella quinlivanii isolated from two unrelated sources in the United Kingdom.
L. rowbothamiiNoLegionella drozanskii sp. nov., Legionella rowbothamii sp. nov. and Legionella fallonii sp. nov.: three unusual new Legionella species.
L. rubrilucensYesIsolation of Legionella rubrilucens from a pneumonia patient co-infected with Legionella pneumophila.
L. sainthelensi1YesInfections due to Legionella sainthelensi in New Zealand.
L. sainthelensi2YesLegionella sainthelensi serogroup 2 isolated from patients with pneumonia.
L. santicrucisNoGrowth of 28 Legionella species on selective culture media: a comparative study.
L. saoudiensisNoInfections due to Legionella sainthelensi in New Zealand.
L. shakespeareiNoLegionella shakespearei sp. nov., isolated from cooling tower water.
L. spiritensis1NoSerological diversity within the species Legionella spiritensis.
L. steeleiNoLegionella steelei sp. nov., isolated from human respiratory specimens in California, USA, and South Australia.
L. steigerwaltiiNoTen New Species of Legionella.
L. taurinenesisNoLegionella taurinensis sp. nov., a new species antigenically similar to Legionella spiritensis.
L. tucsonensisYesLegionella tucsonensis sp. nov. isolated from a renal transplant recipient.
L. tunisiensisNoLegionella tunisiensis sp. nov. and Legionella massiliensis sp. nov., isolated from environmental water samples.
L. wadsworthiiYesLegionella wadsworthii species nova: a cause of human pneumonia.
L. waltersiiNoLegionella waltersii–a novel cause of pneumonia?
L. worsleiensisNoFive new Legionella species isolated from water.
L. yabuuchiaeNoLegionella impletisoli sp. nov. and Legionella yabuuchiae sp. nov., isolated from soils contaminated with industrial wastes in Japan.

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