Legionellosis Caused by Non-Legionella pneumophila Species, with a Focus on Legionella longbeachae

Abstract

Although known as causes of community-acquired pneumonia and Pontiac fever, the global burden of infection caused by Legionella species other than Legionella pneumophila is under-recognised. Non-L. pneumophila legionellae have a worldwide distribution, although common testing strategies for legionellosis favour detection of L. pneumophila over other Legionella species, leading to an inherent diagnostic bias and under-detection of cases. When systematically tested for in Australia and New Zealand, L. longbeachae was shown to be a leading cause of community-acquired pneumonia. Exposure to potting soils and compost is a particular risk for infection from L. longbeachae, and L. longbeachae may be better adapted to soil and composting plant material than other Legionella species. It is possible that the high rate of L. longbeachae reported in Australia and New Zealand is related to the composition of commercial potting soils which, unlike European products, contain pine bark and sawdust. Genetic studies have demonstrated that the Legionella genomes are highly plastic, with areas of the chromosome showing high levels of recombination as well as horizontal gene transfer both within and between species via plasmids. This, combined with various secretion systems and extensive effector repertoires that enable the bacterium to hijack host cell functions and resources, is instrumental in shaping its pathogenesis, survival and growth. Prevention of legionellosis is hampered by surveillance systems that are compromised by ascertainment bias, which limits commitment to an effective public health response. Current prevention strategies in Australia and New Zealand are directed at individual gardeners who use potting soils and compost. This consists of advice to avoid aerosols generated by the use of potting soils and use masks and gloves, but there is little evidence that this is effective. There is a need to better understand the epidemiology of L. longbeachae and other Legionella species in order to develop effective treatment and preventative strategies globally.

Intracellular Behaviour of Legionella Non-pneumophila Strains within Three Amoeba Strains, Including Willaertia magna C2c Maky

“…Even if L. pneumophila is responsible for most legionellosis outbreaks, L. non- pneumophila (Lnp) strains are also involved in legionellosis cases, and often their responsibility is under-recognized due to diagnostic bias [ 2 , 39 , 46 ]. Even though it is now well-known that among the approximately 60 species of Legionella, 50% are able to infect humans [ 47 ], the responsibility for 4% of legionellosis cases can still not be attributed to a known species [ 39 ]. An extensive detection of Lnp strains in water distribution systems demonstrated that 16% of the sampled water was contaminated with Legionella , and that Lnp strains were prevalent [ 48 ].…”

“…The result of a positive PCR test will be designated as a probable case, but not as a confirmed case [ 36 ]. Many studies demonstrate that legionellosis cases were related to Legionella non- pneumophila (Lnp) strains and that these strains are frequently isolated in the environment [ 2 , 37 , 38 , 39 , 40 , 41 , 42 , 43 ]. For example, Steege and Moore detected by means of qPCR on the mip gene the presence of Legionella in 95% of samples, but L. pneumophila was only detected in 1.8% of samples [ 44 ].…”

Legionella feeleii: Ubiquitous Pathogen in the Environment and Causative Agent of Pneumonia

“…Clinically, it is not possible to distinguish Legionnaires’ disease from other forms of pneumonia. Therefore, a proper diagnostic method that enables early identification of Legionella species is critical in the management of patients, as a delay in the provision of an effective treatment against Legionella could increase morbidity and mortality, especially in immunosuppressed patients ( Ruiz et al, 2000 ; Pedro-Botet and Yu, 2006 ; Soler-Majoral et al, 2016 ; Chambers et al, 2021 ). Nowadays, Legionnaires’ disease diagnosis almost exclusively depends on urinary antigen tests, representing 82 and 97% of Legionnaires’ disease confirmation in Europe and the United States, respectively.…”

“…Taking into account its environmental presence, the lack of any reported case could be due to the fact that the diagnostic methods most commonly used in hospitals to confirm cases of Legionnaires’ disease (immunochromatography and ELISA) only detect the L. pneumophila serogroup 1 ( Muder and Yu, 2002 ; Blyth et al, 2009 ). Thus, infections caused by L. feeleii or other species of non- L egionella pneumophila are not detected ( Muder and Yu, 2002 ; Svarrer et al, 2012 ; Vaccaro et al, 2016 ; Chambers et al, 2021 ).…”

“…Therefore, there is a clear need for molecular diagnostic techniques in hospitals to identify Legionella species associated with this disease. In Denmark and New Zealand, PCR protocols are already being employed as routine diagnostic methods ( Svarrer and Uldum, 2012 ; Murdoch et al, 2013 ; European Centre for Disease Prevention and Control, 2017 ; Chambers et al, 2021 ). Some of the most common targets for molecular diagnosis include 16S rRNA and mip (macrophage infectivity potentiator) genes of Legionella spp.…”