After the huge decrease of measles thanks to vaccination, measles reappeared in 2008, with 604 cases reported at the Institut national de veille sanitaire (InVS), then 1,544 cases in 2009 and 2,605 cases up to 2010, June. At the same time, 86 viral strains were detected from saliva samples at the Centre national de référence de la rougeole et des Paramyxoviridae respiratoires (CNR) in 2008, 316 in 2009 and 946 up to August 2010. The reality of the outbreak was confirmed by the increase of the endemic cases: 0.0009% cases in 2008 and 0.004% in 2010, the diffusion to all parts of France, and the more specific attack of infants: 4% in 2008 and 9% in 2010, and of young adults: 17% in 2008 and 38% in 2010. Most of the cases (82%) occurred in non-vaccinated people. The number of hospitalised cases has increased as well, going from 18% in 2008 to 34% in 2010. The strain of this outbreak is a genotype D4. It appeared in 2008 then it spread in 2009 and 2010, representing 19, 75 and 99% of the strains, respectively. All the viruses in this genotype belonged to the Montreal-like cluster described in 1989: Montréal.CAN/89xD4. At the beginning of the outbreak some were closed to a variant which appeared in England in 2007 MVs/Enfield.GBR/14.07(D4), but most of them (95%) are nowidentical to a strain which caused a small focus of measles in the region Vendee at the last trimester 2008: MVs/Montaigu.FRA/43.08(D4). The salivary diagnosis of measles, which was introduced in France in 2005, in parallel to the obligation of reporting measles cases, has been proved very efficient: 75% of saliva are collected in the first four days, and viral RNA was detected in 536 (81%) out the 660 samples received at the CNR up to now in 2010; 136 (21%) saliva had IgM specific antibodies and 18% had neither RNA, nor IgM.
Keywords: genotype D4; measles; outbreak.