The incidence of Legionella pneumophila as the cause of acute ambulatory lower respiratory tract infection.

Seventy-nine ambulatory patients with acute lower respiratory tract infection were evaluated for Legionella pneumophila by acute and convalescent antibody titers. None of the patients met the traditional criteria for the diagnosis of acute infection caused by Legionella pneumophila. Currently accepted criteria for diagnosing legionellosis by serologic means may or may not be applicable to mild respiratory tract infections.