BACKGROUND: Japan was verified as having achieved measles elimination by the Measles Regional Verification Commission in the Western Pacific Region in March 2015. Verification of measles elimination implies the absence of continuous endemic transmission. After the last epidemic in 2007 with an estimated 18,000 cases, Japan introduced nationwide case-based measles surveillance in January 2008. Laboratory diagnosis for all suspected measles cases is essentially required by law, and virus detection tests are mostly performed by municipal public health institutes. Despite relatively high vaccination coverage and vigorous response to every case by the local health center staff, outbreak of measles is repeatedly observed in Aichi Prefecture, Japan. METHODS: @entity805 N and H gene detection by nested double RT-PCR was performed with all specimens collected from suspected cases and transferred to our institute. Genotyping and further molecular epidemiological analyses were performed with the direct @entity4334 sequence data of appropriate PCR products. RESULTS: Between 2010 and 2014, specimens from 389 @entity1 suspected for measles were tested in our institute. Genotypes D9, @entity69982 were detected. Further molecular epidemiological analyses were helpful to establish links between @entity1 , and sometimes useful to discriminate one outbreak from another. All virus-positive cases, including 49 cases involved in three outbreaks without any obvious epidemiological link with importation, were considered as import-related based on the @entity4334 sequence information. Chain of transmission in the latest outbreak in 2014 terminated after the third generations, much earlier than the 2010-11 outbreak (6th generations). CONCLUSION: Since 2010, almost all measles cases reported in Aichi Prefecture are either import or import-related, based primarily on genotypes and @entity4334 sequences of @entity805 detected. In addition, genotyping and molecular epidemiological analyses are indispensable to prove the interruption of endemic transmission when the importations of measles are repeatedly observed.

Case-based surveillance enhanced with XXXX detection/genotyping is essential to maintain measles elimination in Aichi Prefecture, Japan.

@entity1 :: ('9606', 'Species') :: ['patients'] @entity805 :: ('11234', 'Species') :: ['measles virus', 'Measles virus'] @entity69982 :: ('7318;3009;3889', 'Gene') :: ['D8, H1 and B3'] @entity4334 :: ('D009711', 'Chemical') :: ['nucleotide']
@entity805 :: (11234,Species) :: ['measles virus']
