Hepatitis A outbreak response in a vulnerable setting: lessons from southern Portugal

In February 2025, a hepatitis A outbreak emerged in Cabeço do Mocho, Portimão, southern Portugal, an informal settlement lacking safe water and sanitation. The practice detailed in this abstract is relevant to other settings because hepatitis A control in structurally vulnerable communities may require broader and faster measures than standard household-based management. The intervention aimed to identify transmission routes, contain spread and protect exposed residents through a rapid, field-based and intersectoral response. It combined epidemiological investigation, field visits, active case finding, contact assessment, articulation with different Hospital services, primary care and schools, environmental sampling, genotyping and mobile vaccination. Among 109 community members assessed, 13 outbreak cases were identified: four in February, five in March, three in April and one in June, with no cases in May. Hepatitis A virus genome was detected in a household water storage tank, supporting environmental contamination as a contributing factor. On 27-28 February, a mobile vaccination campaign immunized 76 residents, and two additional residents accepted vaccination later. Six cases occurred in residents with vaccination record, suggesting transmission was already established when the campaign took place. In contrast, the four latest cases, occurring in April and June, were in residents not vaccinated during the initial campaign, consistent with initial non-vaccination contributing to prolonged transmission. This experience showed that outbreak control in settings with community-wide exposure must go beyond individual case management. Combining field epidemiology, environmental investigation, mobile vaccination, risk communication and sustained community engagement can improve outbreak control in hard-to-reach populations and may be transferable to other vulnerable urban settings with environmental risk and barriers to vaccine uptake.

Key messages

• Unsafe water and sanitation may justify rapid community-level hepatitis A control, including field investigation and mobile vaccination.

• Place-based responses can improve outbreak control in vulnerable communities, but persistent non-vaccination may prolong transmission.