Underreporting of Leptospirosis in Coastal Municipalities of Ceará: A Descriptive Analysis of the Relationship Between Intense Rainfall, Basic Sanitation, and Notifications Between 2020 and 2024

Leptospirosis is a bacterial zoonosis subject to compulsory notification, with higher incidence in urban areas prone to flooding, especially in the absence of basic sanitation infrastructure. In coastal municipalities of Ceará, where flooding episodes are frequent, an officially low number of reported cases is observed despite high rainfall volumes. This inconsistency may indicate underreporting and epidemiological invisibility of the disease in vulnerable populations exposed to multiple social and environmental determinants. This is an ecological and descriptive study with a temporal approach, involving the municipalities of Itarema, Acaraú, and Itapipoca, in the state of Ceará, between 2020 and 2024. Secondary data were obtained on confirmed leptospirosis cases (SINAN), accumulated monthly precipitation (FUNCEME/INMET), and sociodemographic and sanitation indicators (IBGE and Instituto Trata Brazil). Variables were organized by municipality and month, allowing the description of patterns between intense rainfall (above 200 mm/month) and the number of reported cases. No inferential statistical analyses were performed. The data show accumulated monthly precipitation above 800 mm between March and May from 2020 to 2024, without a proportional increase in notifications. In the first half of 2023, Itarema had 987 mm of rainfall with only one confirmed case; Acaraú, with 843 mm, reported no cases; and Itapipoca reported one case in 2022, even with 910 mm. The scarcity of records made correlation analyses between precipitation, sanitation (3.8% to 19.4%), and poverty unfeasible. Although the data allow descriptive analysis, the low number of notifications prevented statistical analyses. Paradoxically, this low notification in vulnerable areas subject to flooding reinforces the hypothesis of systematic underreporting of leptospirosis in the municipalities analyzed. The findings suggest strong evidence of underreporting of leptospirosis in contexts marked by environmental exposure, sanitation failures, and social vulnerability. Although descriptive, the discrepancy between intense rainfall and few records points to weaknesses in epidemiological surveillance and in access to diagnosis. Decentralizing testing, training professionals, strengthening notifications, and expanding sanitation are essential measures to make visible a disease that may be underestimated.