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/m2 in the Legionella pneumonia group vs. 0.328 liters/m2 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.

An unusually long-lasting outbreak of community-acquired Legionnaires' disease, 2005–2008, Italy

“…Unlike the results of a previous report on the influence of rainfall on LD occurrence [22], data acquired in this case study have shown that the LD incubation period was characterized by scant rainfall events. This meteorological condition together with thermal inversion, which usually affects the Po valley, has probably increased the permanence of the supposed aerosol plume in the atmosphere above the area.…”

Microbiological and Clinical Studies of Legionellosis in 33 Patients with Cancer

“…During the 13 study years, we did notice yearly fluctuation of the isolation of these Legionella strains, and the reason behind this is under investigation. Rainfall is a reported risk factor for legionellosis (31,32). We previously noted that the clinical recovery of rapidly growing mycobacteria, also of an environmental origin, followed the seasonal rise and fall of rainfall in Houston (33).…”

Current and Emerging Legionella Diagnostics for Laboratory and Outbreak Investigations

“…The influence of changes to national water quality standards or adjustments in medical insurance reimbursement patterns is likely minimal (15,124). Interestingly, sporadic LD has been linked to higher-than-average atmospheric temperatures and increased rainfall (or humidity) in several studies, and while a mechanism is not clear, standing road water may play some part in infection (127)(128)(129)(130)(131)(132)(133)(134). A similar increase in the overall European LD incidence has also been documented over the past 20 years but with a possible plateau being reached in the late 2000s (120,135).…”