Abstract Background In September 2023, catastrophic flooding from storms Daniel and Elias struck Thessaly, Greece. We present findings from the post-flood leptospirosis outbreak investigation and key lessons for future preparedness. Methods Ad-hoc active surveillance was set-up to complement national notifications. We used the national case definition for leptospirosis probable and confirmed cases. Diagnostic protocols involved clinical manifestation, PCR, targeted sequencing (blood/urine) and serology. Exposure history was collected via a structured questionnaire. We performed case-series analyses, logistic regression, and Receiver Operating Characteristic curve. Results During the three-month post-flood period, 285 probable and 45 confirmed leptospirosis cases were identified. The post-flood notification rate was 6.5/100,000 population. L. kirschneri and L. interrogans were identified in 33 (87%) and five (13%) of the 38 PCR-confirmed cases, respectively. Two fatalities were attributed to L. interrogans. L. interrogans cases had higher odds of hospitalization (OR:16, 95%CI:1.6-159.2), elevated creatinine (p=0.03), urea (p=0.03), and lower platelets (p=0.02). Urine PCR had the highest diagnostic yield (84%). Leptospirosis cases reported exposure to floodwater (89%), lack of strict adherence to personal protective equipment (100%), and limited awareness of protective measures (25%). Discussion The 2023 Thessaly floods led to a marked rise in leptospirosis incidence, with L. interrogans linked to greater clinical severity. The outbreak highlights the need for public and healthcare workers’ awareness, early diagnosis, species-specific active surveillance, and One Health strategies. Strengthening multisectoral preparedness is critical as climate change increases the risk of similar events in Europe.
Bogogianidou et al. (2026) studied this question.