Journal Article

P59 Measles outbreak in Liguria: molecular surveillance and transmission dynamics in 2024–2025

Lucente, M, Giusto, B, Garzillo, G, Ferrari, S, Faccio, V, Orsi, A, Fraccalvieri, C, Frumento, V, Randazzo, N

2025

Overview

BackgroundMeasles is a highly contagious RNA virus (genus Morbillivirus, family Paramyxoviridae) causing a potentially severe disease. The WHO declared a global epidemiological alert in 2024 due to a resurgence of measles, with over 1,000 cases reported in Italy, reflecting a broader trend of increasing cases worldwide. This situation, worsened by declining vaccination coverage and failure to meet WHO targets, underscores the urgent need for enhanced surveillance and continuous monitoring.Material and MethodsThe Hygiene Laboratory of Policlinico San Martino Hospital in Genoa, a subnational MoRoNet network reference centre for Liguria, conducted molecular tests on urine samples from patients with suspected measles. Nucleic acid extraction was performed using the ELITe InGenius® system (ELITechGroup) and amplification with the Real-Cycler Chic-Out test (Progenie Molecular). Positive samples underwent Sanger sequencing of the N-450 region in the N gene’s C-terminal part. Genotype identification was performed using the Nextclade v3.10.0 platform, and phylogenetic analysis was conducted using the Neighbour-Joining method, aiming to accurately identify transmission pathways.ResultsFrom February to October 2024, 35 measles cases were confirmed in Liguria (mean age: 31 years; 74% men). Most cases presented complications such as diarrhea, pneumonia, thrombocytopenia, or hepatitis, with 7 hospitalizations. Four cases were classified as imported based on travel history. Of the 35 patients, 32 were unvaccinated, while three had received a single dose of vaccine. Genotyping identified 29 samples as genotype D8 (99.9% sequence identity; 100% BLAST identity with strains isolated in Moscow, 2023). Six samples, including four imported cases and two epidemiologically related cases, were genotype B3 (99.7% BLAST identity with strains from Florida, 2016).Between late February and mid-March 2025, 14 measles cases were confirmed in Savona, west Liguria; 12 were linked to hospital exposure. Patients were 64.3% men, with a mean age of 39 years (median 37; IQR 27.5–50). Eight patients were healthcare workers; 12 were unvaccinated (85.7%), one had a single vaccine dose (7.1%), and one had two doses. Genotyping, performed on the 11 samples received to date by the laboratory, revealed samples as genotype B3.Abstract P59 Figure 1Phylogenetic analysis was inferred with neighbor-joining tree. Image was collapsed by cluster size[Figure omitted. See PDF]ConclusionsThe 2025 outbreak, unlike the broader 2024 epidemic, was predominantly hospital-associated, affecting healthcare workers and their contacts, most of whom were unvaccinated. Molecular characterization and sequencing were essential for accurately identifying transmission routes, supporting epidemiological investigations, clarifying transmission dynamics, and effectively interrupting transmission chains. These findings emphasize the importance of molecular tools in measles outbreak management and highlight the need for targeted preventive measures in healthcare settings.

• Publisher: BMJ Publishing Group LTD
• Subject: Epidemics / Genotype & phenotype / Measles / Medical personnel / Phylogenetics / Surveillance / Vaccines