Legionnaires' disease is a relatively common cause of community-acquired
pneumonia and of some outbreaks of
hospital-acquired pneumonia. Moreover, Legionella pneumophila is frequently involved in the aetiology of the subset of
pneumonias that is characterised by severe
clinical course and high mortality. No sure clinical, radiographical or analytical features are useful in differentiating Legionella
infection from other aetiologies of
pneumonia. On the basis of these data, a rational initial therapeutic approach to community-acquired
pneumonia, as well as to
nosocomial pneumonia in certain circumstances, has to include an
antimicrobial agent that is clinically effective against Legionella spp. Clinical studies have provided evidence that
erythromycin is the first-line treatment. An intravenous dosage of 1g every 6 hours as initial
therapy will be effective in most cases. Parenteral treatment may be switched to
oral administration only after clinical response is observed. In vitro susceptibilities and preliminary experimental and clinical results suggest that
clarithromycin will most likely become the preferred treatment once an intravenous preparation is available worldwide. However, orally administered
clarithromycin at the dosage of 500 mg every 12 hours may be recommended in those developing countries in which health systems cannot afford the costs of intravenous
therapy. In the case of clinically severe illness or in seriously immunosuppressed hosts with confirmed
legionellosis, a combined therapeutic approach is warranted.
Rifampicin 600 mg every 12 hours intravenously or orally has to be added to the usual dosage of
erythromycin. Other
alternative therapies, but with less distinct clinical efficacy, that can be combined with
erythromycin are
doxycycline 100 mg every 12 hours intravenously or orally, and intravenous
ciprofloxacin 200 mg every 6 hours.