Legionnaires' disease in Europe: all quiet on the eastern front?

Almost 40 years ago, a large outbreak of pneumonia caused by a previously unidentified agent occurred at a hotel in Philadelphia (PA, USA), affecting 182 persons and causing the death of 29 [1]. All cases had attended a convention of the American Legion, a US wartime veteran service organisation. Both the causative agent of the outbreak and the disease were named after this event: Legionella spp. and Legionnaires’ disease, respectively. Legionella spp. are Gram-negative bacteria found in freshwater environments worldwide and tend to contaminate and thrive in man-made water systems [2]. Legionnaires’ disease is not transmitted from person to person. Infection occurs following inhalation of aerosols containing Legionella or aspiration of Legionella contaminated water, most commonly Legionella pneumophila serogroup 1 [2, 3], but other Legionella species have been documented (table 1) [4]. Legionnaires’ disease usually presents as a severe pneumonia that may be accompanied by systemic symptoms. Known risk factors for Legionnaires’ disease include increasing age, male sex, smoking, chronic lung disease, diabetes and various conditions associated with immunodeficiency [5, 6]. Pontiac fever is a milder form of legionellosis, classically described as an influenza-like illness. Antibiotics with good intracellular action are most effective against any form of legionellosis. Azithromycin and levofloxacin are usually considered as the best first-line option [7, 8]. Mortality from Legionnaires’ disease remains substantial (<10%), even in patients who receive appropriate treatment [9]. A summary of the characteristics of Legionnaires’ disease and Pontiac fever are presented in table 2.