Increased risk of Legionella pneumonia as community-acquired pneumonia after heavy rainfall in 2018 in west Japan.

INTRODUCTION: Japan experienced a heavy rainfall event from June 28 to July 8, 2018, and many casualties were caused by both heavy rainfall and flooding. Few studies have investigated patients' characteristics and the causative pathogens of community-acquired pneumonia before and after heavy rainfall events. The aim of the present study was to evaluate the causative pathogens and clinical characteristics of hospitalized patients with community-acquired pneumonia before and after the heavy rainfall event using prospective cohort data. METHODS: The study was divided into two periods: July to November 2013-2017 (before heavy rainfall) and July to November 2018 (after heavy rainfall). The patients' clinical characteristics and causative pathogens before and after the heavy rainfall were investigated. Regarding the causative pathogens, adjustments were made for precipitation and seasonal patterns. RESULTS: There were no significant differences in the number and clinical characteristics of patients before and after heavy rainfall. However, the frequency of Legionella pneumonia was significantly higher after than before the heavy rainfall event (8.9% vs 3.0%, P = 0.02) and remained significant after adjusting for precipitation and season. Three of 7 Legionella pneumonia patients engaged in reconstruction work and 2 Legionella pneumonia patients had soil exposure. CONCLUSIONS: An increased risk of Legionella pneumonia after not only rainfall and serious flooding, but also following recovery work or soil exposure should be considered.