During 2011, 31 confirmed cases of legionellosis (Legionnaires’ disease [LD]) were reported including 20 cases (65%) among residents of the metropolitan area and 11 cases among greater Minnesota residents. Four (13%) cases died. Older adults were more often affected, with 28 (90%) cases occurring among individuals 50 years of age and older (median, 62.5 years; range, 37 to 88 years). Sixteen (52%) cases had onset dates in June through September. Travel-associated legionellosis accounted for 7 (23%) cases, defined as spending at least 1 night away from the case’s residence in the 10 days before onset of illness.
The criteria for confirmation of a case requires a clinically compatible case and at least one of the following: 1) isolation of any Legionella organism from respiratory secretions, lung tissue, pleural fluid, or other normally sterile fluid by culture, or 2) detection of L. pneumophila serogroup 1 antigen in urine using validated reagents, or 3) seroconversion of fourfold or greater rise in specific serum antibody titer to L. pneumophila serogroup 1 using validated reagents. A single antibody titer at any level is not of diagnostic value for LD. The American Thoracic Society, in collaboration with the Infectious Diseases Society of America, recommends urinary antigen assay and culture of respiratory secretions on selective media for detection of LD. Culture is particularly useful because environmental and clinical isolates can be compared by molecular typing in outbreaks and in investigations of healthcare-associated LD.