TNF and AIDS: Known risk factors include age >50 years, male sex, smoking, alcohol abuse, immunosuppression, and pre-existing cardiopulmonary diseases (21–23).Delayed diagnosis and treatment, coupled with these comorbidities, are associated with increased mortality (24).Because the primary host defense mechanism against Legionella is cell-mediated immunity, individuals with impaired immune function including those with diabetes, malignancies, AIDS, or on immunosuppressive therapies (e.g., corticosteroids, TNF- α inhibitors) are at significantly elevated risk (5, 21, 23, 25, 26).