Impact of flooding on leptospirosis outbreaks in Southeast Asia: a systematic review (2020–2025)

Background Leptospirosis is a zoonotic disease strongly associated with flooding, particularly in tropical regions such as Southeast Asia. With climate change driving more frequent and severe flood events, understanding this relationship is essential for public health preparedness. This review synthesizes recent evidence on the link between flooding and leptospirosis outbreaks in Southeast Asia, with emphasis on risk factors and preventive measures. Methods A systematic review was conducted in accordance with PRISMA 2020 guidelines and registered in PROSPERO (CRD420251063300). PubMed, Scopus, ScienceDirect, and Google Scholar were searched for studies published between January 2020 and December 2025. Eligible studies reported leptospirosis incidence or outbreaks in relation to flooding or heavy rainfall in Southeast Asia. Reviewers independently screened, extracted data, and assessed study quality using JBI appraisal tools. Findings were synthesized narratively due to heterogeneity. Results Eight studies met the inclusion criteria, representing Malaysia ( $$n=3$$ ), Indonesia ( $$n=2$$ ), Thailand ( $$n=2$$ ), and the Philippines ( $$n=1$$ ). Most studies reported temporal or spatial associations between flooding and leptospirosis incidence, often with a lag of one to three months. Environmental drivers included rainfall, humidity, stagnant water, and inadequate drainage. Social and behavioural risk factors included rodent exposure, poor use of personal protective equipment (PPE), male gender, and skin wounds. Preventive strategies highlighted were Geographic Information System (GIS)-based risk mapping, meteorological early warning systems, targeted health education, and PPE provision, though empirical evaluation of interventions was limited. Conclusions Flooding is a consistent determinant of leptospirosis outbreaks in Southeast Asia. Strengthening disaster preparedness through predictive modelling, integrated One Health surveillance, and equity-focused interventions is essential. Investments in diagnostics, infrastructure, and early warning systems, particularly for rural and low-income populations, are critical to reduce future outbreaks under worsening climate conditions.