N Engl J Med 374 (5): 497 - 498, 2016. doi: 10.1056/NEJMc1505356 Diseases caused by Legionella species Legionella infection is more frequent and more severe in the following: Older people Patients with diabetes or chronic obstructive pulmonary disease (COPD) Cigarette smokers Immunocompromised patients (typically with diminished cell-mediated immunity) The lungs are the most common site of infection; community - and hospital-acquired pneumonia may occur.