Leptospirosis, a re-emerging, zoonotic infectious disease caused by spirochetes of the genus Leptospira, is particularly endemic to tropical regions. The global burden of leptospirosis is estimated to be 1.03 million cases and 58,900 deaths annually [1]. Despite efforts to improve prevention [2] and outcomes [3,4], global attention toward leptospirosis remains limited. Low- and middle-income countries in Southeast Asia, the Pacific, and Central and South America bear a disproportionately high burden of leptospirosis, driven by climate disasters, poor infrastructure, and social deprivation [1]. In contrast, high-income countries mainly report sporadic or imported cases [5].

The clinical spectrum of leptospirosis is broad, ranging from mild manifestations such as fever, chills, myalgia, and headache to severe phenotypes characterized by acute liver failure, acute kidney injury, pulmonary hemorrhage, disseminated intravascular coagulation [6], and acute respiratory distress syndrome [7]. Severe cases may require admission to the intensive care unit (ICU), renal replacement therapy, and mechanical ventilation [8,9]. Reported case fatality rates vary across studies, ranging from 0.9 % to 14.0 % [[10], [11], [12], [13]]; higher rates are observed in non-endemic regions [1]. Differences in outcomes may be attributable to variations in healthcare systems and diagnostic thresholds. Furthermore, the quality of care for a given disease is generally lower when healthcare providers have limited experience in managing the condition [[14], [15], [16]].

Japan is primarily located in the temperate climate zone, except for the southwestern islands of Okinawa, which lie in the subtropical zone and are endemic for leptospirosis [17,18]. Therefore, Japan is unique in that endemic and non-endemic areas of leptospirosis coexist in one country and are covered by the same healthcare system. Therefore, this study aimed to compare the patient characteristics, treatments, and outcomes of leptospirosis between the endemic and non-endemic areas in Japan to gain insights to improve the quality of care in non-endemic regions.