Persistence of the Same Strain ofLegionella pneumophilain the Water System of an Italian Hospital for 15 Years

In 2004, an outbreak of legionnaires disease occurred in a hospital in northern Italy with a water system that had been disinfected multiple times since 1990 and equipped with a continuous disinfecting system. Molecular typing linked the outbreak to contamination of the hospital water system and demonstrated the persistence of a predominant strain of Legionella pneumophila for 15 years.