During 2007, 31 confirmed cases of legionellosis (Legionnaires’ disease [LD]) were reported including 19 cases (61%) among residents of the metropolitan area and 12 cases (39%) among Greater Minnesota residents. One (3%) case-patient died. Older adults and elderly persons were more often affected, with 23 (74%) cases occurring among individuals 50 years and older (median age, 57 years; range, 37 to 72 years). Twenty-three (74%) cases had onset dates in June through September. Travel-associated legionellosis accounted for seven (23%) 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 treatment guidelines for community-acquired pneumonia recommend 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.
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.