In February 2016, the National Reference Center for Leptospirosis reported two confirmed cases of leptospirosis requiring hospitalization in intensive care among inmates at a correctional facility. This zoonosis, caused by bacteria of the genus Leptospira, is contracted through contact of broken skin or mucous membranes with the urine of infected animals or a contaminated damp environment. The presence of rodents on the premises and the vulnerability of certain inmate populations prompted a retrospective cross-sectional investigation, the objectives of which were to document the cluster of cases, identify additional undiagnosed cases of leptospirosis, and determine potential risk exposures in order to guide management measures. Medical records of individuals who visited the infirmary between January 11 and February 19, 2016, were reviewed. For all suspected cases, clinical and epidemiological information was collected and supplemented through a questionnaire administered to the individuals. For cases suggestive of leptospirosis, blood testing (PCR, serology) to detect leptospirosis infection was offered. Ultimately, 1,229 records were reviewed (corresponding to 78.1% of consultations during the study period). This analysis identified 33 possible cases, 21 of whom agreed to undergo blood testing. All serological results were negative. Interviewing the two confirmed cases revealed a skin wound in one, and high-risk activity (cleaning around the building and collecting trash) without prior vaccination in the other. This investigation contributed to the implementation of new preventive measures to limit rat infestations, and to the strengthening of prevention efforts through the use of personal protective equipment and catch-up vaccination for individuals engaged in high-risk activities.