Measles cluster in Northern Portugal: enhancing surveillance strengths

Abstract Although measles was declared eliminated in Portugal in 2015, outbreaks persist, despite high vaccination coverage. The last outbreak in the northern region was in 2017. Portugal has a Surveillance System implemented for mandatory communicable diseases (SINAVE) integrating clinical, epidemiological and laboratory data. In 2021, WHO expressed concern about the low sensitivity of measles surveillance and urged Portugal to strengthen its surveillance practices. Our study aims to describe a measles cluster in northern Portugal during the first trimester of 2024. Data from measles cases from the first trimester of 2024 were collected from SINAVE. Contact tracing and Public Health (PH) intervention data was sent by Local Public Health Authorities through a survey designed for that purpose. A total of 70 suspected cases were reported and investigated: 6 cases were laboratory confirmed and 64 were discarded. The confirmed cases had a mean age of 28 years (all adults), with 50% female. The mean notification time was 0,3 days. The index case was imported (Mauritania) and unvaccinated, leading to 2 secondary cases. Five cases had 2 doses of a measles vaccine, with 1 case being a health professional. Additionally, 1 case was imported from France. For 2 cases the source of infection could not be unequivocally identified and no travel history during incubation period. A total of 851 contacts of confirmed cases were identified. Although sustainable transmission is not evident in our region, measles is being introduced through migration and tourism. Despite clinical awareness, strengthening early case detection is essential to enforce effective control measures. PH teams have been working tirelessly to trace clusters origins, gathering large number of contacts and adapting strategies for sustained control. In a globalized world, ensuring surveillance sensitivity is paramount. Integrating other data sources in surveillance routine is crucial for upholding Measles-Free Status compliance. Key messages • Measles must take centre stage on our agenda. • Reinforcing surveillance, integrating additional data sources, is crucial for heightened sensitivity and prompt response.