Measles epidemics and seroepidemiology of population in Wujin, Changzhou city, Jiangsu province, China 2015

The measles epidemic was rather severe in Wujin 2015, and a seroprevalence survey of measles antibody was conducted during June to September 2015 in Wjin district of Changzhou city. Blood samples were collected from community health population and convenient samples of residual blood from hospitals. Measles-specific IgG levels were measured by ELISA assay. A total of 122 measles cases were reported 2015 in Wujin district with an incidence of 8.31 per 100 000 populations. A large proportion of measles cases were adults ≥20 years (62.30%) and infants aged <18 months (28.69%). Floating population accounted for 68.57% of all cases. 1070 blood samples aged from 9 months to 49 years old were collected and the overall seroprevalence and geometric mean titer (GMT) of measles were 82.71% and 551.19 mIU/ml, respectively. Although the seroprevalence among children aged 9 months to 4 years was consistently over 90%, it began to decrease since 24 months, and till the age of ≥10 years, the seroprevalences were all <80%, however, the seroprevalence rised to above 80% in people over 40 years. There were no significant differences between the two blood sample sources in the level of seroprevalence and GMT. Also no significant differences were observed in the seroprevalence of measles and GMT levels between genders. The seroprevalence and GMT in people with measles vaccination were higher than those without measles vaccination or people whose measles vaccination are unknown (P < 0.001). Our study indicated that the adult measles cases have become a serious problem in Wujin district, which may mainly relate to the increasing size of the floating population with low measles vaccine coverage. The seroprevalence of measles decreased dramatically with increasing age since teenagers, which may mainly caused by waning vaccine-induced immunity. Therefore, it is necessary to strengthen measles vaccine in these people especially floating population.