LEGIONELLA - World Health Organization

Ideally, specimens for culture should be taken before antibiotic treatment is initiated, although
Legionella has been isolated from lower respiratory tract specimens and blood after several
days treatment with erythromycin. Sputum should be considered for culture even when not
purulent (Ingram & Plouffe, 1994). Respiratory specimens that are particularly difficult to
obtain, such as lung tissue, pleural fluid or bronchoalveolar lavage (BAL), should be cultured
if received on a routine basis (Stout, Rihs & Yu, 2003).
Legionella has been successfully isolated from lower respiratory tract specimens, including
BAL, transtracheal aspirate, endotracheal suction specimens, pleural fluid, lung biopsy and
expectorated sputum. In the early phase of illness, legionellosis is often accompanied by a dry
cough with little sputum. In this context, the low number of organisms present outside the
lungs and the inhibitory effect of oral flora reduce the sensitivity of the culture method. In
severe forms of legionellosis, especially in immunocompromised patients, bacteraemia (bacterial
spread to the bloodstream) can occur, with a frequency of approximately 30% in patients
with severe legionellosis. Sometimes, legionellae are found in samples from extrapulmonary sites,
especially from postmortem specimens (e.g. liver, spleen, pericardial fluid, kidney wounds,
cutaneous abscess or vascular grafts).
Benefits and limitations of using culture media
Culture of Legionella is often the most sensitive detection method, and has high specificity
(>99%) (Edelstein, 1987). Culture is particularly important for diagnosis in:
• cases in which severe pneumonia causes respiratory failure
• immunocompromised patients
• nosocomial infections
• cases in which disease is caused by any legionellae other than L. pneumophila serogroup 1.
Some legionellae cannot be grown on routine Legionella culture media and have been termed
Legionella-like amoebal pathogens (LLAPs), because they grow in certain host species of
amoeba. These organisms have been isolated and maintained in culture by co-cultivating the
bacteria with their protozoan hosts. One LLAP strain was isolated from the sputum of a
pneumonia patient by enrichment in amoebae. This LLAP strain is considered to be a human
pathogen (Fry et al., 1999; Marrie et al., 2001). Other LLAP strains may be human pathogens,
although this is difficult to prove because they cannot be detected by conventional techniques
used for legionellae. Recently, three LLAP strains were named Legionella species (Adeleke et
al., 2001; La Scola et al., 2004).
0 LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS