In our series, etiology was known in 41.25 percent of cases, but the mortality rate of all community-acquired pneumonias was 5 percent, which is surprisingly low and similar to the rates in other series. In prospective studies, the incidence of pneumonia due to L pneumophila ranges from 3.8 percent to more than 30 percent, depending on several factors. It is obvious that regional differences exist, but there also are differences depending on whether the studies are based on hospitalized or ambulatory patients.
Thus, in hospital-based case series the incidence of Legionnaires’ disease is greater because patients with Legionnaires’ disease usually require hospital admission; that is why L pneumophila is the second cause of community-acquired pneumonia in our hospital. The number of diagnostic methods used in each hospital also has a great influence on the incidence of Legionnaires’ disease. In this way, the systematic culture of respiratory specimens of all patients with community-acquired pneumonia in BCYE-alpha medium probably explains that the incidence of community-acquired pneumonia caused by L pneumophila in our hospital has increased from 2.5 percent in 1982 to 198311 to 7 percent in 1988 to 1989.