LEGIONELLA - World Health Organization

Evaluation of antimicrobial agents
When extracellular, legionellae are susceptible to a wide range of antimicrobial agents. However,
in an infection, where the microorganism is inside the cell; the only antimicrobial agents that
are clinically useful are those that achieve high intracellular concentrations. Therefore, new
drugs have to be evaluated in regard to:
• their minimum inhibitory concentration values against Legionella spp.
• their activity in cellular culture systems
• their activity in animal studies
• the clinical context.
Suggested treatments
Only a few small, controlled clinical studies of antibiotic treatment for Legionnaires’ disease
have been completed; hence, the evidence for treatment recommendations is limited (Thornsberry,
Baker & Kirven, 1978; Yoo et al., 2004; Yu et al., 2004). One small clinical study showed
that treatment with fluoroquinolone pefloxacin gives patients a higher survival rate than
treatment with erythromycin (Dournon et al., 1990).
The new macrolide antibiotics, such as clarithromycin and azithromycin, show more effective
in-vitro activity and a better intracellular and tissue penetration than erythromycin, as do the
quinolones. Beta-lactam antibiotics are not effective against Legionnaires’ disease, but are the
first choice of antibiotics for pneumococcal pneumonia, and are used together with macrolides
to treat severe pneumonia. Where a rapid diagnostic test for Legionnaires’ disease is not in
use, many people presenting with this disease are simply treated with macrolides plus betalactam
antibiotics, because a delay in the application of appropriate therapy for Legionella
pneumonia significantly increases mortality (Stout & Yu, 1997).
Table 1.8 lists the various treatments for different groups of patients with Legionnaires’ disease.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS