| BackgroundInfluenza is a common acute respiratory infections diseases caused by influenza viruses, which is mainly transmitted through air and droplets and spread easily. Influenza virus is RNA virus and can be divided into three types:A, B and C. Each type also contains different subtypes. There are no long-term immunity in population because of the virus’high variability. All age groups are susceptible to them, which could cause outbreaks easily. Influenza occurs globally with an annual attack rate of 10%-20% in all population. Influenza is the only infectious disease which could prevail periodically. In the 20th century, four flu pandemics occurred worldwide, three of which originated in China, one of "hotspots" of influenza diseases. In order to monitor activity of influenza, the World Health Organization created the Global Influenza Surveillance Network in 1952. Influenza is the first infectious diseases under global surveillance. Influenza-Like Illness (ILI) surveillance data had been proven to effectively reflect the activity patterns of influenza virus.The occurrence of influenza is not only influenced by pathogenicity of influenza virus, population susceptibility and social health conditions, but also influenced by natural environment. There is significant difference in climatic conditions from south to north of China, while the characteristics of influenza activity also showed a trend that emerged from south to north overall. Shandong Province is located in the eastern coast of China. Complex topography and more significant temperature difference in north-south than east-west may result in regional differences in incidence of influenza. This study aims to explore the characteristics of influenza epidemic in the Shandong area, as well as flu-related meteorological factors by analyzing ILI surveillance data and meteorological data in Shandong Province, which could provide a basis for prevention, control and early warning and forecasting of influenza.Objectives1. To explore the characteristics of incidence and epidemic trends of ILI in Shandong Province.2. To quantitatively study the correlation between ILI% and meteorological factors to provide scientific basis for influenza control and prevention.MethodsData from ILI surveillance, cluster and outbreak monitoring as well as meteorological data in Shandong province from 2009 to 2014 were collected and cleaned. Descriptive statistical analysis, including statistical tables, figures, line charts, and spatial distribution maps were applied to analyze the epidemiological characteristics of ILI Chi-square test was used to test the difference in positive rates of specimen across genders. The univariate analysis using the Spearman rank correlation test was conducted. All factors with P＜0.10 in univariate analysis were included in multivariate panel data regression model with significance level of 0.05. Panel data is the data of many individuals at different times, which consists of three dimensions:individual, time and variable. Panel data unit root test using Breitung test, LLC test, ADF-Fisher test, PP-Fisher test and IPS test were used to conduct panel data unit root test; Fixed effects model and random effects model for panel data were selected based on Hausman test. The statistical software used included Microsoft Office 2013, IBM SPSS Statistics 19.0, ArcGIS 10.0 and Stata12.0.Results1. There were reported 738,572 ILI cases and 34,812,120 total visits of outpatient and emergency in Shandong Province during 2009-2014. The ILI% was 2.12%. The age distribution of ILI cases were as follows:0-4 years (53.46%),5-14 years (22.80%),15-24 years (8.21%),25-59 years (11.96%), older than 60 years (3.56%). The peak of ILI% was from the 45th week (November) to the ninth week (March) of next year, especially in the 3th-6th week. The cities with higher average ILI% were Dezhou (4.41%), Weifang (4.14%), followed by Qingdao, Dongying, Binzhou and Tai’an. Jinan, Liaocheng, Heze, Jining and Linyi reported the lowest ILI%. Overall, the ILI% in northeast coast regions was higher than that in the southwest inland areas.2. During 2009-2014,83,886 ILI specimens were collected in Shandong Province and 81,029specimens (96.59%) were tested in laboratory, among which 13,661 specimens were positive. The positive rate was 16.86%. Specimen collected from national ILI sentinel hospital surveillance sites accounted for 93.45%. The positive rate of specimen collected from summer was lower than those from winter. Among specimens of national ILI sentinel hospital surveillance cases, the top four population were students (31.91%), kindergarten children (21.25%), scattered children (11.28%), worker (6.82%). No significant difference was observed between specimen positive rate of men and women in each year. The annual predominant strain were as follows:A/H1N1 in 2009, type B in 2010 and 2012, Type A in 2011 and 2013, A/H1N1, seasonal H3 and Yamagata in 2014. In general, type A and B occurred alternately every year. The predominant strains in different areas were similar.3. From 2009 to 2014,192 cluster and outbreak flu were reported. The most frequency month were January, November and December except for the year of 2009. Jining was the most frequently reported city, followed by Zibo and Weifang. The least frequently reported cities were Liaocheng, Zaozhuang, Rizhao, Laiwu and Binzhou. Outbreaks mainly occurred in students, kindergarten children and teachers.4. At the significance level of 0.05, we found the meteorological factors significantly statistically correlated with ILI% are weekly average pressure(IRR: 0.982,95%CI:0.975-0.989), weekly average wind speed (IRR:0.992,95%CI: 0.988-0.996), weekly average temperature (IRR:0.989,95%CI:0.988-0.990), weekly average relative humidity (IRR:1.003,95% CI:1.001-1.006), and weekly cumulative sunshine time(IRR:0.997,95% CI:0.994-0.999).Conclusions1. ILI frequently occurred from November to March of next year in Shandong. Seasonal change of ILI incidence is obvious. Winter and spring are flu seasons.2. The population aged 0-4 years accounted for majority of ILIs, followed by 5 to 14 years,25 to 59 years,15 to 24 years and 60 and older years of age. The 0-4 year-old children were more susceptible to influenza virus and did not have significant seasonal trend of influenza throughout the year. Schools are "hotspots" of ILI outbreaks.3. The ILI% in northeast coast regions is higher than that in the southwest inland areas in Shandong.4. Type A and B of influenza virus occurred alternately every year. The predominant strain of different areas was similar in the same year, but there were differences in adjacent years in the same area.5. We found meteorological factors statistically significant negative correlated with ILI% were weekly average pressure, weekly average wind speed, weekly average temperature, and week cumulative sunshine time. However, weekly average relative humidity was positive correlated with ILI%. |
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