Lower serum phosphate levels in patients with Legionella pneumonia relative to patients with non-Legionella pneumonia

INTRODUCTION: Few studies have evaluated serum phosphate levels in patients with Legionella pneumonia admitted to hospitals in Japan. This study aimed to assess serum phosphate levels among inpatients with Legionella pneumonia on admission and compare them to those of inpatients with non-Legionella community-acquired pneumonia. METHODS: This case-control study included patients aged ≥16 years who were treated for Legionella pneumonia from April 2011 through March 2017 and those aged ≥16 years who were treated for non-Legionella community-acquired pneumonia from August 2014 through July 2015. Legionella pneumonia was diagnosed based on a positive result on the urinary antigen test, as well as radiographic examinations. Serum phosphate levels on admission were compared between Legionella and non-Legionella patients. In addition, serum phosphate levels on admission and on hospital day 5–7 were compared in Legionella patients. RESULTS: We evaluated 8 Legionella patients and 61 non-Legionella patients. Median serum phosphate levels on admission were 1.90 and 2.80 mg/dL in Legionella and non-Legionella patients, respectively (P = 0.008). By hospital day 5–7, serum phosphate levels in Legionella patients had increased to 2.61 mg/dL (P = 0.029, relative to admission), which did not significantly differ from those of non-Legionella patients on admission (P = 0.372). CONCLUSION: Serum phosphate levels on admission were approximately 32% lower in Legionella pneumonia patients compared to non-Legionella pneumonia patients, but both were comparable by hospital day 7.