During 2009, 30 confirmed cases of legionellosis (Legionnaires’ disease [LD]) were reported including 17 cases (53%) among residents of the metropolitan area and 13 cases among Greater Minnesota residents. Three (10%) cases died. Older adults and elderly persons were more often affected, with 22 (73%) cases occurring among individuals 50 years of age and older (median, 58 years; range, 43 to 88 years). Eleven (37%) cases had onset dates in June through September. Travel-associated legionellosis accounted for 5 (17%) 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 spp., 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 recommends urinary antigen assay and culture of respiratory secretions on selective media. Culture is particularly useful because environmental and clinical isolates can be compared by molecular typing in outbreaks and in investigations of health care-associated LD.