title: Rainfall is a risk factor for sporadic cases of Legionella pneumophila pneumonia.
abstract: It is not known whether rainfall increases the risk of sporadic cases of Legionella pneumonia. We sought to test this hypothesis in a prospective observational cohort study of non-immunosuppressed adults hospitalized for community-acquired pneumonia (1995-2011). Cases with Legionella pneumonia were compared with those with non-Legionella pneumonia. Using daily rainfall data obtained from the regional meteorological service we examined patterns of rainfall over the days prior to admission in each study group. Of 4168 patients, 231 (5.5%) had Legionella pneumonia. The diagnosis was based on one or more of the following: sputum (41 cases), antigenuria (206) and serology (98). Daily rainfall average was 0.556 liters/m(2) in the Legionella pneumonia group vs. 0.328 liters/m(2) for non-Legionella pneumonia cases (p = 0.04). A ROC curve was plotted to compare the incidence of Legionella pneumonia and the weighted median rainfall. The cut-off point was 0.42 (AUC 0.54). Patients who were admitted to hospital with a prior weighted median rainfall higher than 0.42 were more likely to have Legionella pneumonia (OR 1.35; 95% CI 1.02-1.78; p = .03). Spearman Rho correlations revealed a relationship between Legionella pneumonia and rainfall average during each two-week reporting period (0.14; p = 0.003). No relationship was found between rainfall average and non-Legionella pneumonia cases (-0.06; p = 0.24). As a conclusion, rainfall is a significant risk factor for sporadic Legionella pneumonia. Physicians should carefully consider Legionella pneumonia when selecting diagnostic tests and antimicrobial therapy for patients presenting with CAP after periods of rainfall.
authors.affiliation: Department of Infectious Diseases, Hospital Universitari de Bellvitge, IDIBELL (Institut Dinnvestigació Biomèdica de Bellvitge), Universitat de Barcelona, Barcelona, Spain. carolgv75@hotmail.com
authors.forename: Carolina
authors.initials: C
authors.lastname: Garcia-Vidal
authors.forename: Maria
authors.initials: M
authors.lastname: Labori
authors.forename: Diego
authors.initials: D
authors.lastname: Viasus
authors.forename: Antonella
authors.initials: A
authors.lastname: Simonetti
authors.forename: Dolors
authors.initials: D
authors.lastname: Garcia-Somoza
authors.forename: Jordi
authors.initials: J
authors.lastname: Dorca
authors.forename: Francesc
authors.initials: F
authors.lastname: Gudiol
authors.forename: Jordi
authors.initials: J
authors.lastname: Carratalà
mesh_terms: D006801:Humans; D016952:Legionella pneumophila / Q000472:pathogenicity*; D007877:Legionnaires' Disease / Q000175:diagnosis / Q000453:epidemiology*; D011014:Pneumonia / Q000175:diagnosis / Q000453:epidemiology*; D011891:Rain; D012307:Risk Factors