During 2006, there were 27 confirmed cases of legionellosis (Legionnaires’ disease [LD]) reported. This included 11 cases (41%) among residents of the metropolitan area and 16 cases (59%) among Greater Minnesota residents. Four (15%) case-patients died. Older adults and elderly persons were more often affected, with 20 (74%) cases occurring among individuals aged 50 years and over (median age, 56 years; range, 31 to 85 years). Ten (37%) cases reported onset dates in June through September. Travel-associated legionellosis accounted for 14 (52%) cases, defined as spending at least 1 night away from the case’s residence in the 10 days before onset of illness.
Confirmed LD case criteria includes X-ray confirmed pneumonia and positive results for one or more of the following tests: culture of Legionella sp., or detection of L. pneumophila, serogroup 1 infection by Legionella urinary antigen, direct fluorescent antigen, or by acute and convalescent antibody titers with a four-fold or greater rise to >1:128. A single antibody titer at any level is not of diagnostic value for LD. For detection of LD, the Infectious Diseases Society of America treatment guidelines for community-acquired pneumonia recommend urinary antigen assay and culture of respiratory secretions on selective media (http://www.journals.uchicago.edu/CID/journal/issues/v37n11/32441/32441.html). Culture is particularly useful because environmental and clinical isolates can be compared by molecular typing in outbreaks and in investigations of healthcare-associated LD. Starting in 2005, CDC recommended routine assessment of travel history among LD cases so that travel-associated LD clusters or outbreaks could be more readily and quickly detected. Clinical guidance on legionellosis and other resources can be found at: http://www.cdc.gov/legionella/index.htm.