Postflood Leptospirosis Outbreak Response Due to Leptospira interrogans and Leptospira kirschneri in Central Greece, 2023: Comparison of Laboratory and Clinical Manifestations.

BACKGROUND

In September 2023, catastrophic flooding from storms Daniel and Elias struck Thessaly, Greece. We present findings from the postflood 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, polymerase chain reaction (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 analysis.

RESULTS

During the 3-month postflood period, 285 probable and 45 confirmed leptospirosis cases were identified. The postflood notification rate was 6.5/100 000 population. Leptospira kirschneri and Leptospira interrogans were identified in 33 (87%) and 5 (13%) of the 38 PCR-confirmed cases, respectively. Two deaths were attributed to L interrogans. Patients with L interrogans had higher odds of hospitalization (odds ratio, 16 [95% confidence interval, 1.6-159.2]), elevated creatinine (P = .03) and urea (P = .03), and lower platelet counts (P = .02). Urine PCR had the highest diagnostic yield (84%). Patients with leptospirosis reported exposure to floodwater (89%), lack of strict adherence to personal protective equipment (100%), and limited awareness of protective measures (25%).

CONCLUSIONS

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.