In 2014, 58 confirmed cases of legionellosis (1.1 per 100,000 population) were reported in Minnesota residents. The criteria for confirmation of a legionellosis case are a clinically compatible illness and at least one of the following: 1) isolation of any Legionella organism from respiratory secretions, lung tissue, pleural fluid, or other normally sterile site 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. Five cases were diagnosed by culture alone. A single antibody titer of any level is not considered diagnostic for legionellosis. Patients positive by polymerase chain reaction only are classified as suspected cases; in 2014, there were 5 suspected cases of legionellosis reported in Minnesota residents.
Of the 58 confirmed cases, 57 (98%) had pneumonia, 55 (95%) were hospitalized for a median duration of 5 days (range, 1 to 35 days), 25 (43%) were admitted to an intensive care unit, 16 (28%) required mechanical ventilation, and 1 (2%) died. Thirty-nine (67%) cases were male. Older adults were more often affected, with 39 (67%) cases occurring among individuals 50 years of age and older (overall median age, 56 years; range, 25 to 91 years). Twenty-seven (47%) cases had onset dates in June through September. Thirty-three (57%) cases were residents of the metropolitan area and 25 (43%) were residents of Greater Minnesota. Of the 47 cases for which information was available, 16 (34%) were classified as travel-associated, defined as spending one or more night away from their residence (excluding health care facilities) in the 10 days prior to onset of illness; 14 (30%) had exposure to a health care facility in the 10 days prior to onset of illness. There was one legionellosis outbreak detected with 2 cases (1 reported in 2013, and 1 reported in 2014) associated with exposure to a decorative water wall in a casino. An additional case was part of an outbreak in another state associated with exposure to a contaminated hotel hot tub.
The Infectious Diseases Society of America and the American Thoracic Society, in their consensus guidelines on the management of community-acquired pneumonia in adults, recommend urinary antigen assay and culture of respiratory secretions on selective media for detection of legionellosis. Culture is particularly useful because environmental and clinical isolates can be compared by molecular typing in outbreaks and in investigations of health care-associated legionellosis.
- For up to date information see>> Legionellosis (Legionella): Legionnaires' Disease and Pontiac Fever
- Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2014