OUTBREAKS of legionnaires' disease (LD) have been linked to aerosols from evaporative condensers and cooling towers,1,2 whirlpool spas,3 respiratory therapy equipment,4 and humidifiers.5 An association between shower use and LD has been hypothesized but not epidemiologically demonstrated.6-11 Prevention of LD is limited by a lack of understanding of the ecology of Legionella pneumophila. Monitoring aerosolproducing sites for L pneumophila can be misleading since the bacteria are found often in water sources without a known disease association.12
Factors essential for Legionella multiplication in water are poorly understood, but the bacteria multiply extracellularly on supplemented culture media.13,14 Nutritional requirements of the genus are unlikely to be met in most water sources; however, these bacteria do multiply inside protozoa,15-17 which are common to aquatic environments. Legionella pneumophila grows in water samples with amoebae but not in those without viable amoebae.17 Recognition of the association
Breiman RF, Fields BS, Sanden GN, Volmer L, Meier A, Spika JS. Association of Shower Use With Legionnaires' Disease: Possible Role of Amoebae. JAMA. 1990;263(21):2924–2926. doi:10.1001/jama.1990.03440210074036
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