Prevalence of Legionnaires' disease and investigation on risk factors: results of an italian multicentric study

Background: The aims of the study were to detect nosocomial and community-acquired Legionnaires’ disease among patients with pneumonia recovered in Italian hospitals, to improve knowledge on the disease frequency, and to characterise environmental, personal, genetic and immune risk factors associated with the disease appearance (case-control study). Methods: In six big hospitals, an active surveillance lasting four years was carried out to detect cases among recovered pneumonia. The protocol included the systematic detection of urinary L. pneumophila antigen (EIA), search of the microorganism in respiratory secretions, and seroconversion (IFA) as confirmation test. Cases were included, after obtaining informed consensus, in a case-control study to evaluate environmental, clinical and personal characteristics associated with the disease. As controls, both healthy subjects and patients affected by other pneumonia were recruited. Results: We detected 189 cases on 6,032 examined pneumonia (3.13%), 174 were community and 15 nosocomial-acquired. Prevalence varied between 1.5 and 6.1% according to the surveyed hospital. One hundred and twenty-six patients and 142 controls entered in the case-control design. Pre-existing immune-pathologies were associated with the disease, whereas higher smoking and co-morbidity were risk factors of all pneumonia. A significant decrease in CD16 (natural killer) cell number was found in patients compared with both control groups. Furthermore, significant alterations in iron metabolism and serum trace elements were found. Polymorphisms of the chemokines receptors genes (ccr5 and ccr2) were also evaluated. Conclusions: Our active clinical surveillance scheme was able to identify 189 cases between 2001 and 2004, contributing to increase reports in Italy, where about 600 cases for year are notified. The rate of infection in recovered pneumonia was about 3%, confirming results of other similar surveys. The preliminary results of the case-control study show that cases have peculiar, although not sufficiently studied, alterations in both immune and biochemical parameters, which deserve further investigations.