Case-based surveillance of measles in Sicily during 2012-2017: The changing molecular epidemiology and implications for vaccine strategies

Following the indication of the World Health Organization, a national plan for the elimination of measles was approved in Italy and this included the improvement of the molecular surveillance of measles viruses and the interruption of indigenous transmission of the disease. Nevertheless, large outbreaks continue to occur in almost all regions of the country, including Sicily. Here we describe the epidemiology and molecular dynamics of measles viruses as a result of the measles surveillance activity carried out by the “Reference Laboratory for Measles and Rubella” in Sicily over a 5-year period. Biological samples of 259 suspected measles cases were tested for viral RNA detection and a total of 223 (86.1%) were classified as laboratory confirmed. The median age of confirmed measles cases was 21.0 years and about half of them were adults aged 19 years and older. Overall, one-third of the patients showed clinical complications and these latter were more common among adults than children (44.9% vs. 25.7%). The vast majority of measles cases were unvaccinated (94.2%, n = 210). The phylogenetic analysis of 221 measles virus nucleotide sequences revealed sporadic detections of genotypes D4 and H1, while endemic circulation of genotypes D8 and B3 was documented. Genotype D8 was associated with epidemics occurred between 2013 and 2016, whereas genotype B3 was more recently introduced into Sicily characterizing the current measles outbreak. The results of this study confirm the autochthonous co-circulation of viral variants belonging to different genotypes during the study period, and emphasizes the need of measles surveillance programmes in order to investigate the viral dynamics, the pathways of disease transmission, and to eventually adapt the development of successfull vaccine formulations.

遵循世界卫生组织（World Health Organization, WHO）的指导方针，意大利获批了全国性麻疹消除计划，其中涵盖麻疹病毒分子监测体系的优化与阻断该疾病本土传播的相关举措。尽管如此，该国几乎所有区域（包括西西里岛）仍持续出现大规模麻疹暴发疫情。本研究基于西西里岛麻疹和风疹参考实验室（"Reference Laboratory for Measles and Rubella"）历时5年的麻疹监测工作，阐述了当地麻疹病毒的流行病学特征与分子演化动态。研究人员对259例疑似麻疹病例的生物样本开展病毒RNA检测，最终223例（占比86.1%）被判定为实验室确诊病例。确诊病例的年龄中位数为21.0岁，约半数患者为19岁及以上的成年人。整体而言，三分之一的患者出现临床并发症，且成人并发症发生率显著高于儿童（44.9% vs 25.7%）。绝大多数确诊病例未接种麻疹疫苗（94.2%，n=210）。对221株麻疹病毒核苷酸序列的系统发育分析显示，研究期间偶有D4、H1基因型毒株检出，而D8与B3基因型毒株则呈现地方性循环传播特征。D8基因型毒株与2013至2016年间的暴发疫情相关，而B3基因型毒株为近期传入西西里岛，成为当前当地麻疹暴发疫情的主导毒株。本研究结果证实，研究期间存在不同基因型麻疹病毒变异株的本土共同循环传播现象；同时强调，需持续开展麻疹监测工作，以深入解析病毒动态、疾病传播途径，并最终助力高效疫苗配方的优化研发。