Legionellosis in Military Health System beneficiaries, 1998-2013

Legionellosis is an infection caused by exposure to mist or vapor contaminated with Legionella bacteria. During the 16-year surveillance period, 73 cases of legionellosis were identified in active component service members; 37 were identified among the reserve component; and 1,044 were identified among all other beneficiaries of the Military Health System (MHS). Of the total 1,154 cases of legionellosis, 11 percent (n=126) were confirmed cases (i.e., reportable medical events); 52 percent (n=599) were probable cases (i.e., hospitalizations); and 37 percent (n=429) were suspected cases (i.e., ambulatory visits). Most of the cases (59%) were identified in individuals aged 60 years and older. The annual number of cases increased during the surveillance period and demonstrated a seasonal trend with more cases occurring in the summer and early fall. Recent trends in the incidence of legionellosis among MHS beneficiaries and civilian populations in the United States highlight the importance of correctly identifying the etiologic agents of bacterial pneumonia and submitting reports of cases of legionellosis through the appropriate reporting system.