The Study On The Epidemiological Characteristics Of Measles And The Immunity Level Between Local Population And Floating Population In Zhoushan City

Background&ObjectiveMeasles has been further controlled since1999when the government controlled measles accelerately, however, measles outbreak appeared in some areas of Zhoushan city. There are many main reasons, such as, the decline of natural infection rate, the swarming of large number of floating population, the change population composition, the frequently flowing of population. Moreover, the increase of blank immunization population, the operation of cold chain system in vaccine storage and transport processes, may directly affect the vaccine titer too. Otherwise, the immune success rate of meales vaccine is still unclear in Zhoushan city. To provide a scientific basis for measles prevention and control, and to provide protection for measles elimination goal in2012, in this study, we analysed the epidemics of meales in Zhoushan city, tracked the changes of measled vaccine in all aspects of storage and use, evaluated the measles vaccine immunity before and after immunization, investigated the immune status of the local healthy population and floating population, and analysed if there were differences between the immunity levels of the local population and floating population in each age group. Materials&Methods1. Analysis of measles epidemiological characteristicsThe measles epidemic data derived from the communicable diseases reporting system and measles monitoring system from2001to2010in Zhoushan city.2. Monitoring of measles immunization level2.1. Object and methods2.1.1Tracking and monitoring the quality of measles vaccine.Five tubes measles vaccine of the same batch were extracted from each sampling point including Zhoushan City CDC, Putuo District CDC, Liuheng Center Hospital vaccination clinics, before vaccination and after vaccination, and were delivered to Zhejiang provincial CDC for detection of effectiveness in low-temperature.2.1.2Monitoring the success rate of immunization.2-3ml blood were collected from40babies before immunization and1month after immunization in each Putuo District and Daishan County, and were detected by Micro-hemagglutination inhibition test (HI).2.1.3Monitoring of immunity levels3ml venous blood were collected from7age group including under1year old,1-2,3-4,5-6,7-14,15-19and≥20years, in which group contained at least120people with half local population and half foreign population in Dinghai District, Putuo District, Daishan Country and Shengsi Country. And the immuninty levels were determined by Micro-hemagglutination inhibition test (HI).2.2. Determine criteriaVaccine titer was determined by micro cell culture plate method. Measles vaccine was qualified if logTCID50/0.1ml>2.5.Monitoring of vaccination success rate and level of immunity:Serum IgG antibody levels greater than1:2can be judged as positive, greater than1:8can be considered up to the level of protection. Serum IgG antibody was negtive or with low antibody(<1:8) before vaccination and become positive or with≥4fold grwth after vaccination can be judged as Immune successfully. The rate of successful basic immunization was more than85%can be considered as up to standard.ResultsFrom2001to2010, the total number of suspected measles paitinents was554from the city’s monitoring report system, of which confirmed case of measles was316, in which local patients accounted for73.10%(231/316) and foreign patients accounted for26.90%(85/316). The average incidence rate of measles was3.11/105, of which local patients accounting for2.21/105. The constituent ratio of local patients to foreign patients decreased year by year. The distribution of cases covered4countries, occurred every year which mainly concentrated in March to June (n=250), and covered each age group in which the number of patients under1year old and>20years was244, accounting for77.22%. In measles cases,48cases (15.19%) had been vaccinated,103cases (32.59%)had no history of vaccine inoculation, and the vaccination history of the other165cases (52.22%) was unknown. In1to14years group, there was significant difference between local and foreign patients in history of vaccine inoculation(χ2=21.42, P<0.001).Seven age group (n=496) were investigated to monitor the immunity levels of local healthy population. The positive rate of measles antibody was79.03%, the rate of protection was64.52%, the GMT was1:5.98, of which the highest group was1-2years group, and the lowest group was≥20years group. The positive rate or the protection rate of measles contained statistically significant difference among each age group (χ2=46.81, P<0.001). Seven age groups (n=548) were investigated to monitor the immunity levels of floating population. The positive rate of measles antibody was75.55%, the rate of protection was58.58%, the GMT was1:5.72, of which the highest group was1-2years group, and the lowest group was≥20years group. The positive rate or the protection rate of measles contained statistically significant difference among each age group (χ2=35.12, P<0.001).The positive rate and protection rate of measles antibody level of local and foreign population both showed a downward trend with the increasing of age. There was no statistically difference in the positive rate of measles antibody between local an foreign population (χ2=1.20, P>0.05). The protection rate of measles in local population was64.52%, there was statistically difference compared with the foreign population (χ2=3.88, P<0.05). In local and foreign population, the positive rate of measles was95.00%and70.31%, respectively, the protective rate of measles was91.67%and59.38%, respectively, there was significantly difference between them (χ212.93、17.22, P<0.001). The positive rate of the other age groups exist no statistically difference, however, the protection rate exist statistically difference among under1year group,3-4years group and7-14years group (χ2=5.60、9.71、10.34, P<0.05). In local and foreign population with under15years, the protective rate of measles was69.81%and60.00%, respectively, and there was statistically difference between them (χ2=7.43, P<0.05).In this study,10copies of two batches measles vaccine were collected from municipal CDC cold room, in which the qualified rate was100%.16copies from the other four sampling points showed81.25%qualified. In80school-age children, the positive rate was18.75%before vaccination, and96.25%after vaccination, there was significantly difference (χ2=98.31, P<0.001). The immunization was successful with85%success rate, in which the Putuo District was successful with87.5%and Daishan District was failure with82.5%.ConclusionsA. From2001to2010, the total number of confirmed measles was316from the city’s monitoring report system, of which foreign patients accounted for26.90%(85/316), and the average incidence rate of measles was3.11/105. The incidence was in the lower level which was mainly disseminated, and outbreaked occasionlly. The season peak appeared from March to June. Cases under1year old children and>20years adults were the main cases. Cases from floating population showed an upward trend, and became the main population.B. The total qualified rate of measles vaccine in Zhoushan was81.25%, lower than the level of other areas in Zhejiang Province. The all unqualified vaccine come from inoculation points of primary prevention.C. The immunization was successful with85%success rate, but there was imblance in different regions.D. The positive rate of measles in local and foreign population was79.03%and75.55%, respectively, the level of immunity showed a downward trend with the increasing of age.E. Under15years old, the immunity level of floating population was lower than the local, especially the1-2years group.