Study On The Epidemic Characters Of Influenza In Shanghai

Shanghai located at the east China.Its geography area is 6340 square kilometers. At the end of 2007,Shanghai has the resident population of 18,500,000.It is estimated that the population will surpass to 20,000,000 before 2010.Shanghai will become one of the world's only several metropolis that populations surpass 20,000,000.Shanghai is not only china's important port it is also one of the Asian's most main economic centers.The communication of international personnel and the cargo are frequent.China is the influenza-prone area.the people who infected each year are more than 100,000,000.There are four times of influenza pandemic in the last century and each time China and Shanghai were involved.As the influenza is one kind of the acute infectious disease,it can cause outbreak easily.In this study,from January 2006 to August 2008 in the city of Shanghai we set up 26 sentinel hospitals of influenza to report data every week.According to the description methods of epidemiological trends and time series analysis research,I synthesize the etiology,serology test results, as well as information on the outbreaks to analysis and describe the characters of influenza in Shanghai.And I also try to explore the trends and pattems of conduct warning and forecast of influenza.So as to make the incidence of influenza in shanghai be at a relatively low level.From January 2006 to August 2008,the city's 26 Influenza Surveillance Sentinel hospitals reported 276,482 cases of influenza-like illness(ILI),the cases of each week were between the numbers of 829 to 8137 and the average number was 1989 cases. The percentage of ILI visitors was in the range of 6.38%to 0.75%,and the average was 1.84%.The number of ILI and the percentage of ILI changed in the basic trend. In 2006,there are three peaks distribution to winter(Jan),spring(Mar-April) and summer(Aug) seasons.In 2007 and 2008 there were only two peaks in each year. They are the winter(Feb 2007,Mar 2008) and summer(Aug 2007,Aug 2008) peaks. In recent years,with the appearance of warm winter,the climate sense of winter has been postponed,so the winter peak changed into spring peak gradually.I used the results of virus isolation to determine the non-influenza pandemic seasons.On the basis of 82 weeks data I calculated the baseline of percentage of ILI visitors per week with 75th percentiles(P75) and the baseline was 2.56%.From January 2006 to Aug 2008,the winter,spring and summer peak of 2006 was over the baseline,and the winter and summer peak of 2007 were close to the baseline,in the year 2008,the percentage of ILI visitors was below the baseline.To analysis the data by region,the percentage of ILI visitors from urban was(1.27 percent) lower than that in suburb(3.01%),which may be due to the differences in the distribution of medical resources and the habit of getting medical treatment.It may not be true that the ILI incidence of suburb is greater than the incidence of urban. In all of the ILI,the percentage of patients aged from 0 to 4 was 24%,and 22%for the age from 5 to 14 and 14%for 15 years old to 24.The percentage for adult ages from 25 to 59 was 33%and 7%for the patients over the age of 60.The incidence of major was focused on children under the age of 15.The outbreaks of influenza were concentrated in the winter season.The peak of outbreaks was from Jan to Mar.It will popular with the change of predominated strain.The outbreaks were also concentrated in the primary school of lower age(22,57.89%) and we should also pay more attention to the high incidence in special school such as the school for blind children (14.78%) and community hospitals(12.82%).From January 2006 to August 2008,there had 3746 throat swab samples of ILI been detected d by the Flu-lab of shanghai CDC and 673 of them were positive,the positive rate was 17.97%.Of all the positive samples,the number of H1N1 were 117 (17.38%),H3N2 were 315(46.81%),B(Victoria line) were16(2.38%),B(Yamagata line) were 225(33.43 percent).According to the results of virus isolation per month, the predominated strain had changed in the last 3 years.In the first half of 2006,the predominated strain was B virus and it changed into H1N1 in the second half.It turned to H3N2 in 2007 and was substituted by B virus in the second half until April 2008.In May 2008,the H3N2 virus gradually regained the dominant position.The changes of predominated strains matched the type of outbreaks.Serological testing showed that the positive rate and antibody titers of children below the age of 15 were higher than that in other age groups.On the contrary,positive rate and antibody titers of the elderly over the age of 60 were both lower.That not only suggested us there was a higher incidence of low age group and a low incidence of the elderly.But also a decline in immunity in the elderly what could cause serious consequences.I used the software of SPSS11.5 to processing the weekly data from January 2006 to August 2008.In accordance with the ARIMA model of the product formula,I combine the model of ARIMA(p,d,q)(P,D,Q) S and got the forecast equation: lgY_t=0.8791gY_t-1+0.4181gY_t-26-0.3671gY_t-27+0.5821gY_t-52-0.5121gY_t-53.I established the mode by using the data from week 1-130,and the data from week 131-139 to test the prediction of the model.As a result,the forecast and the actual value are almost 100%match.The ARIMA forecast model has a good role for the prevention and control of influenza in Shanghai.