Measles outbreak under the Leaning Tower of Pisa in Italy

Abstract Background Measles cases in Italy (58,9 mln population) were 8 in 2021, 15 in 2022 and 43 in 2023. Between January and April 2024 there were 213 cases in Italy, with higher incidence in children. Pisa Local Public Health Department (201073 population) experienced a measles outbreak in the same period. Methods Cases were classified according to Decision (EU) 2018/945. A bidirectional tracing (backward and forward) was conducted to identify transmission chain and contacts of cases. Immunization status was checked on Regional Vaccination Registry. Results 33 suspected measles cases were notified in Pisa between 21st January and 17th April 2024: 16 by General Practitioners and 17 by Hospital Emergency Room. Additionally, 1 undiagnosed case was found during the epidemiological investigation. 2 notifications were withdrawn by General Practitioner because of lack of the diagnostic criteria. Laboratory analysis confirmed 24 cases. Last confirmed case occurred on 23rd February, while not confirmed cases occurred mostly in the last part of the period (6 in a row from 3rd March to 17th April), suggesting an infodemic effect. Women were more affected than men (17 vs. 7). Except for 2 babies (9 months and 1 year old age), the outbreak affected young adults with a mean age of 40 yo. Hospitalization rate was 37,5%. The first 5 unrelated cases occurred between 19th and 21st January. A second wave involved 13 people, 12 of them were related to a single case. Transmission occurred in Emergency Room (7), in a mall (1) and in the neighborhood (4). A third wave involved 4 cases (family contacts). 2 cases were imported from Sicily and Spain. All cases were unvaccinated, 2 were migrants. Around 950 contacts were traced. Conclusions In Pisa, high vaccination coverage of children < 2years of age (≥95%) protected school population and cases to spread, but there are pockets of unvaccinated adults which could allow measles circulation. Key messages • An effective public health response is required to contrast increasing measles cases in EU/EE countries. • As recommended by ECDC, public health services need to close immunity gaps, addressing catch-up actions towards adults and vulnerable groups as migrants.