Legionellosis, 2015

During 2015, 51 legionellosis cases (0.9 per 100,000 population) were reported. 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 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 of any level is not considered diagnostic for legionellosis. Patients positive by PCR only are classified as suspected cases; in 2015, there were 5 suspected cases.

Of the 51 confirmed cases, 50 (98%) had pneumonia. All 51 cases were hospitalized, with a median duration of acute hospitalization of 6 days (range, 1 to 46 days). Twenty-nine (57%) were admitted to an intensive care unit, 17 (33%) required mechanical ventilation, and 9 (18%) died. Thirty-three (65%) cases were male. Older adults were more often affected, with 42 (82%) cases occurring among individuals ≥50 years of age (overall median age, 62 years; range, 24 to 82 years). Twenty-seven (53%) cases had onset dates in June through September. Thirty-one (61%) were residents of the metropolitan area and 20 (39%) were residents of Greater Minnesota.

Of the 48 cases for which information was available, 14 (29%) were classified as travel-associated, defined as spending 1 or more night away from their residence (excluding healthcare facilities) in the 10 days prior to onset of illness. Of 34 cases with exposure information available and no travel, 12 (35%) had exposure to a healthcare facility in the 10 days prior to onset of illness. There was one legionellosis outbreak identified in Minnesota, with 2 cases associated with poor plumbing at a restaurant. There were also 2 cases in Minnesota residents associated with outbreaks in different states, one in Missouri and one in New York City. The remaining 47 cases (92%) were sporadic.

• 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, 2015