BACKGROUND:
In October 2025, an outbreak of Acute Diarrheal Disease (ADD) was reported in the Meio da Mata Indigenous Village, Porto Seguro, Bahia, Brazil. The community is located in a remote forested area and relies on an untreated collective water supply sourced from an unprotected cacimba and inadequately structured artesian wells. Laboratory analyses revealed microbiological contamination in water samples, indicating sanitary vulnerability and risk of waterborne disease transmission. This report describes an intrasectoral surveillance response integrating environmental, sanitary, and epidemiological health actions to investigate and control the outbreak.

METHODS:
An intrasectoral approach was carried out involving Environmental, Sanitary, and Epidemiological Surveillance, in coordination with Indigenous Health services. Field activities included on-site inspections, household visits, assessment of water capture and storage systems, identification of vulnerable groups, interviews with community leaders, and photographic records. Water samples were analyzed by the Central Public Health Laboratory (LACEN), and clinical and epidemiological data were reviewed to support risk assessment.

RESULTS:
The investigation identified significant sanitary vulnerability related to the absence of water treatment, deficiencies in water supply infrastructure, proximity of septic pits to water sources, and intermittent electricity affecting water pumping. Microbiological analyses detected opportunistic pathogens, including Bacillus cereus, Morganella morganii, Serratia marcescens, Citrobacter spp., Enterobacter spp., and Ralstonia mannitolilytica. Stool sample analysis identified Norovirus, indicating a predominantly viral outbreak potentiated by water contamination. Emergency measures included health education, restriction of contaminated water sources, environmental sanitation actions, and provision of sodium hypochlorite for temporary water treatment.

CONCLUSIONS:
This experience highlights the importance of intrasectoral coordination for timely investigation and control of waterborne disease outbreaks in Indigenous communities. Strengthening water supply infrastructure, ensuring continuous water quality monitoring, and improving sanitary conditions are essential to reducing health risks. Integrated surveillance actions with community engagement and health education, are fundamental to preventing recurrent outbreaks and protecting vulnerable populations.