Epidemic characteristics of measles and genotype distribution of measles virus in Ningbo municipality,2004-2015

Objective To examine epidemic characteristics of measles and genotype distribution of wild strains of measles virus in Ningbo municipality from 2004 to 2015 and to provide evidences for making measles control strategies.Methods Surveillance data on measles epidemic and wild strains of measles virus isolated in Ningbo municipality from January 2004 through 2015 were collected.The nucleoprotein (N) genes of the isolated strains were amplified with reverse transcriptase PCR (RT-PCR) and sequenced for homologous analysis.Results The annual measles morbidity were 9.93,21.09,2.46,12.73,33.38,4.10,2.41,0.93,6.60,2.11,2.30,and 2.74 per 100 000 for the years from 2004 to 2015,respectively,and the morbidity showed a declined trend generally (χ_trend²=2743.496,P<0.010).There were measles case reports in every month throughout a year and more measles cases were reported from February to May in a year,accounting for 66.74% of all the reported cases.There were measles case reports in all the 11 counties or districts of Ningbo municipality and the top three administrative regions with higher average annual morbidity were Haishu,Jiangbei,and Jiangdong district,with the total reported measles cases of 520,485,and 450 and the average morbidity rate o f 13.81,13.33,and 12.19 per 100 000 people,respectively.Of all the cases reported,23.13% were the infants less than 8 months old;20.89% were the small children aged 8 mouths to 7 years;4.02% were the children aged 8-14 years;6.40% were the adolescents at the ages of 15-19 years;and 45.56% were persons over 20 years old.Of the 90 wild strains of measles virus isolated during the period,11were B3 genotype,79 were H1 genotype (73 of H1a genotype and 6 of H1b genotype).Conclusion The annual measles morbidity declined generally and the strain of H1a genotype was a predominant wild measles virus in Ningbo municipality from 2004 to 2015.