Incidence and risk factors associated with progression to severe pneumonia among adults with non-severe Legionella pneumonia

BACKGROUND: Legionella species are important causative organisms of severe pneumonia. However, data are limited on predictors of progression to severe Legionella pneumonia (LP). Therefore, the risk factors for LP progression from non-severe to the severe form were investigated in the present study. METHODS: This was a retrospective cohort study that included adult LP patients admitted to a 2,700-bed referral center between January 2005 and December 2019. RESULTS: A total of 155 patients were identified during the study period; 58 patients (37.4%) initially presented with severe pneumonia and 97 (62.6%) patients with non-severe pneumonia. Among the 97 patients, 28 (28.9%) developed severe pneumonia during hospitalization and 69 patients (71.1%) recovered without progression to severe pneumonia. Multivariate logistic regression analysis showed platelet count ≤150,000/mm(3) (odds ratio [OR], 2.923; 95% confidence interval [CI], 1.100–8.105; P=0.034) and delayed antibiotic treatment >1 day (OR, 3.092; 95% CI, 1.167–8.727; P=0.026) were significant independent factors associated with progression to severe pneumonia. CONCLUSIONS: A low platelet count and delayed antibiotic treatment were significantly associated with the progression of non-severe LP to severe LP.