Measles outbreak linked to an international dog show in Slovenia - primary cases and chains of transmission identified in Italy, November to December 2014.

A Filia (antonietta.filia@iss.it)1, F Riccardo1,2, M Del Manso1, P D’Agaro3, F Magurano4, A Bella1, Regional contact points for measles surveillance5 1. Infectious Diseases Epidemiology Unit, National Centre for Epidemiology, Surveillance and Health Promotion, Istituto Superiore di Sanità, Rome, Italy 2. European Programme for Intervention Epidemiology Training (EPIET), European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden 3. Department of Medical, Surgical and Health Sciences, University of Trieste, Trieste, Italy 4. Department of Infectious, Parasitic and Immune-mediated Diseases, Istituto Superiore di Sanità, Rome, Italy 5. The regional contact points for measles surveillance are listed at the end of the article


To the editor:
Recently, Grgič-Vitek et al. reported a measles outbreak in Slovenia linked to an international dog show held in Vrtjoba/Šempeter from 8 to 9 November 2014, involving 44 cases [1].Genotype D8 was identified in seven cases and viral sequences were deposited in the World Health Organization (WHO) MeaNS database [1].
In December 2014, the European Centre for Disease Prevention and Control (ECDC) conducted a Rapid Risk Assessment of the outbreak and recommended that, since the dog show had exhibitors from 27 European countries, national public health authorities from these countries should consider contacting the exhibitors to verify their measles vaccination status and illness histories, and perform contact tracing for identified cases [2].
The dog show was held near the Italian border and over 350 of the 670 registered exhibitors had reported an Italian address.The Infectious Diseases Epidemiology Unit of the Istituto Superiore di Sanità (ISS), in collaboration with regional and local health authorities in Italy contacted the Italian exhibitors, as recommended.
We obtained the names of registered exhibitors from the Slovenian authorities through the Early Warning and Response System (EWRS), listed these by region of residence and sent them to the regional health authorities (RHA) of 16 regions.We asked RHAs to (i) verify Eighteen measles cases [3] were identified and reported to the national measles surveillance system: 11 primary cases, three secondary cases and four tertiary cases (Figure ).

Figure
The median age of the cases was 31 years (range 5-52 years); 16/18 cases were female.Vaccination status is known for 17/18 cases of whom 15 were unvaccinated and two had received one dose.Seventeen cases tested IgM/PCR positive against measles.Genotype D8 was isolated in three primary cases and phylogenetic analysis showed that viral sequences were identical to each other and to those identified in Slovenia [1].Sequencing and genotyping results for additional cases are pending.
The epidemiological, serological and molecular characterisation of cases linked to international mass gatherings is helpful in tracing international measles virus transmission pathways and identifying susceptible population groups, and will become increasingly important as Europe approaches measles elimination.
Although it is possible that additional cases will be identified in Italy, local transmission appears limited to date, suggesting that the public health response to the outbreak was timely in the regions involved.Measles vaccination coverage is suboptimal in Italy (88% for the first dose at two years of age, in 2013), ranging from 85.8% to 93.1% in the regions of residence of the participants at this event, and pockets of susceptible persons are known to exist, especially among adolescents and young adults [4].The fact that most Italian cases linked to the dog show were also young adults, further underlines the importance of closing immunisation gaps against measles in this population group.It is well known that the risk of measles transmission can be high at mass gatherings because of the large number of participants from many different countries (with varying vaccination and incidence rates) in a crowded setting [5].National public health authorities should raise awareness among the population of the risk of measles transmission during travel and mass gatherings, and of the importance of verifying one's immunity before departure.Governments hosting mass gatherings should work with event organisers to include measles immunisation advice for participants and visitors in the event information packages [6].
Number of measles cases linked to an international dog show in Slovenia, by date of rash onset, Italy, November-December 2014 (n=18) [3]es were classified according to the European Commission case definitions of 8 August 2012[3].