Application Of Infectious Disease Dynamics Model In Early Warning Of Varicella Epidemic Situation And Evaluation Of Intervention Measures In Changsha City

Objective:（1）To investigate the prevalence,epidemiological and general characteristics of varicella in Changsha of Hunan Province.（2）To explore the time characteristics of the varicella epidemic cycle,find out the inflection point of the epidemic speed change in the epidemic cycle,and then get the warning week.（3）Establishing a SEIR model of varicella transmission in Changsha through a series of mathematical theory methods.Further,to predict the incidence of varicella,and to explore the prevention and control effects of vaccination,isolation and other control measures in varicella outbreak.Methods:（1）The data used in this study was obtained through the Chinese Information system for Disease Control and Prevention.We collected all reported cases of chickenpox in Changsha from 7th week2008 to 42th week 2017.The diagnostic criteria are in accordance with the Diagnosis and Treatment for chickenpox.（2）According to the patient’s onset time,it was sorted into the number of cases in the week to analyze the cycle law of varicella epidemic in Changsha;and to use the Logistic differential equation model to fit all the epidemic periods separately,obtain the parameters K and N which were calculated by the incident cases of actual weeks,and then get the parameter C according to the differential equation,and finally we get the inflection point of the speed change of these cycles,that is,"the epidemic acceleration week" and"the warning week".（3）Based on a outbreak of varicella in a school in Changsha,according to the basic transmission model of varicella in the infectious disease population model method,combined with the characteristics of varicella transmission in Changsha,thus,to construct the model of varicella SEIR in Changsha City of Hunan Province.Obtain relevant parameters in the model by consulting relevant literature,survey reports,and statistical data.And estimate the infection probability（β）by 1stopt,Matlab7.1,Berkeley Madonna 8.3.18 and other tools.Further,using the SEIR model to fit the actual data,predict the incidence trend,and explore the control effect of emergency measures such as emergency vaccination and isolation of patients on the outbreak of chickenpox by changing the model and model parameters or conditions.Results:（1）This study collected 58228 cases,including 3 deaths,from the Changsha Municipal Center for Disease Control and Prevention in Hunan Province through the National Disease Surveillance Information System for all cases of varicella reported between 2008 and 2017;and the analysis found that the incidence rate was the lowest in 2009（5.22/10,000）;the highest in 2017（13.04/10,000）;and the difference in the incidence of varicella between the years was statistically significant（P<0.05）.（2）The average number of reported cases of varicella patients in Changsha City,Hunan Province from 2008 to 2017 was 112.97,with an average growth rate of 12.97%.The incidence rate showed a significant annual growth trend.（3）Analysis of the reporting time of all chickenpox patients found that the incidence of chickenpox in Changsha City showed two peaks every year,from April to July and November to January,and there were cases of chickenpox in each month.Among them,the average number of reported cases in December was the highest（about 917.3cases）,and the September was the least（about 194.3 cases）.（4）There are two peaks of Varicella at each year in Changsha city.One is the peak in summer-autumn corresponding to the 8^th-38^th week,the other is the peak in winter-spring corresponding to the time from the 38^th week to the 7^th week next year.（5）Analyzed by Logistic differential equation model shows that the"epidemic speed week"average value of summer-autumn is about the 16^th week,while the winter-spring is about the 45^th week,and the standard deviation is all about 1 week.So the"recommended warning week"of summer-autumn is the 15^th week,and that of winter-spring is the 44^th week,thereby raising the concern of chickenpox and thus preventing the outbreak of chickenpox.（6）The SEIR model has a good fitting effect on the outbreak of chickenpox.We can get that there is no statistically significant difference between the simulated theoretical value and the actual value（c²（28）0.608,P（29）.005）.The goodness-of-fit test shows that the model has better simulation effect（7）R²（28）.0816,P（27）0.01（8）.（7）Simulation analysis by SEIR model shows that when the varicella patients are strictly isolated,the cumulative number of cases is up to 13people,which significantly reduced;the vaccination has ion efficiency reaches 0.7,the TAR%can be reduced.obvious control effect on the varicella epidemic,and the higher the inoculation rate,the better the control effect.When the inoculation rate reaches 50%,the TAR can be reduced to 0.56%;With the efficient changes in ventilation and disinfection,there is no significant difference in the number of patients,but only the peak time is delayed.The more efficient the ventilation and disinfection,the longer the epidemic will be after the peak day,and the longer the epidemic will last.Only when the disinfection efficiency reaches 90%,the number of cases can be slightly less,but the duration of the epidemic is also significantly prolonged.（8）In addition,the simulation comparison of joint prevention and control of different interventions shows that the combination of"isolation+vaccination"had better prevention effect.When the vaccination rate reached 0.3,the TAR could be reduced to 0.28%.The three prevention and control measures were combined at the same time.The effect of the three measures are the most significant,and when the inoculation rate reaches 0.2,the TAR can be controlled below 1.0%;In addition,the study found that when the efficiency of ventilation and disinfection is low,the combined prevention and control effect is similar to that after removal.Only when the ventilation and disinfect.Conclusion:（1）The average growth rate of varicella patients in Changsha was 12.97%in 2008-2017,and the rate showed a trend of increasing.There are two epidemic cycles of varicella in Changsha every year,which are the peaks of summer-autumn and winter-spring.（2）The study shows that the"epidemic speed week"average value of summer-autumn is about the 16^th week,while the winter-spring is the 45^th week,and the standard deviation is all about 1 week.So the"recommended warning week"of summer-autumn is the 15^th week,and that of winter-spring is the 44^th week,thereby raising the concern of chickenpox and thus preventing the outbreak of chickenpox.（3）It is found that case isolation and vaccination can effectively control the development of school varicella epidemic,and the greater the vaccination rate,the better the prevention and control effect;However,ventilation and disinfection measures have no obvious control effects on the development of school chickenpox epidemic;The combined control effect of case isolation and vaccination is better than single measures;When school varicella breaks out,comprehensive interventions for case isolation and vaccination can be adopted,and the greater the vaccination rate,the better the prevention and control effect,meanwhile the additional ventilation and disinfection can be used as an aid.