Study On Epidemic Features And Related Factors Of Human Brucellosis In Shandong Province

BACKGROUNDBrucellosis, known as "undulant fever", "Mediterranean fever" and "Malta fever", is a highly infectious zoonosis caused by Brucella. The main sources of infection of human brucellosis are sick sheep, cattle, pigs, dogs and so on. Brucellosis can occur through contact with infected animals or consumption of their products, digestive tract and respiratory tract. Brucellosis is serious harmful to human health, development of animal husbandry and economic trade.Brucellosis is prevalent in Asia, Sub-Saharan Africa, the Middle East, the Mediterranean, some countries of Latin America, and South Eastern European Region. Human brucellosis which is a public health concern has lead to serious economic loss and high global health burden, particularly in developing countries. Shandong was one of the top 10 provinces where great number of cases was reported. Brucellosis has been reported in all 17 cities since 2005. In addition, increasing number of cases and growing scope of natural foci are also observed.At present, complicated epidemic situation of brucellosis and growing scope of natural foci in China do great harm to human health and bring serious disease burden. Shandong was considered as a typical northern epidemic area. In present study, we describe the epidemic features and related factors of human brucellosis on basis of data of human brucellosis of Shandong province, which provide important information on its prevention and control.OBJECTIVE1. To describe the people distribution, time and place of human brucellosis in population, time and space by traditional epidemiological methods, methods of time series analysis and spatial epidemiological methods2. To explore related factors of human brucellosis by a 1:2 case-control study, which can provide scientific information for its prevention and control.MATERIALS and METHODS1. Source of materials(1) Descriptive study:Information of cases from year 2004 to 2014 was collected from Shandong Diseases Reporting Information System (SDIS).(2) Case-control study:a 1:2 case-control study in LiJin, Qingyun, Zhangqiu, Yuncheng, Wudi, Qingzhou and Linzi., Human brucellosis cases in these areas from January to December 2013 were which from provided by Shandong Diseases Reporting Information System (SDIS).2. Methods(1) Descriptive study:SPSS 16.0 was used to analysis the information of human brucellosis, including age, gender, occupation and other demographic characteristics. Distribution of counties and the season were also described. Methods included χ2 test, linear trend χ2 test, and Kruskal-WallisH rank sum, with significance level of 0.05. GIS software (ArcGIS 9.3) and the software of spatial aggregation analysis (SatScan 7.0) were applied to explore the temporal and spatial distribution with analysis of spatial clustering analysis and clustering time. Time series analysis and establishing model were based on software of SAS 9.0(2) Case-control study:The database on the basis of a questionnaire was established by EpiData 3.0. SPSS16.0.was used in data analysis. The Student’s Mest, Wilcoxon rank sum test as well as Chi-square test were performed to identify risk factors for human brucellosis. We analyzed the data using univariate and multivariate logistic regression models to examine their associations between influencing factors and brucellosis. Multiplicative interaction model examined the interaction between lacks of protective measures with risk factors, with significance level of 0.1. The effects was evaluated by odds ratio (OR)95% confidence intervals (CIs) and Population Attribute Risk Percent (PAR%),with significance level of 0.05,with SPSS 16.0 software.RESULTS1. Epedemic features(1) Three-dimension distribution of human brucellosisDuring 2005-2014, the incidence had been increasing year by year, with the average growth rate of 35.56%. Brucellosis have occurred in every month and the peak occurrence time of this disease was in March to August (67.41%). May was the most peak month (13.90%). The number of cases in the spring and summer was decreasing year by year. Male case was 76.17%(4542/6171)and the male/female ratio was 2.79:1. The age of cases was between 5 month and 89 years, the age group of 46-55 was the highest (24.6%). Farmer was the predominant occupation group among the cases. Cases have been reported in 17 cities in Shandong province. The top 5 high morbidity cities were Heze, Weifang, Binzhou, Jining, Zibo, and the proportions were 16.53%(1003/6067)、12.44%(755/6067)、11.44%(694/6067)、10.25%(622/6067)、 9.35%(567/6067) separately. The number of affected counties increased year by year (linear χ=421.57, P<0.0001), and 139 counties had been affected in 2005-2014. The number of affected counties were 20、18、24、23、33、43、68、94、117、133 separately. Most cases were reported from the general hospitals, accounting for 41.94%(2588/6171), and the cases with clinical diagnoses and laboratory diagnoses were 10.71%(661/6171) and 88.64%(5470/6171) separately.(2) Spatial analysis:The incidence rate of human brucellosis increased from 0.0382/100000 (35 cases) to 0.6205/100000 (598 cases), with annual average incidence rate as 0.2111/100000 and the incidence was evidently increased. The value of M(0.3753)showed that this disease was seasonal, with the epidemic months between March and June, accounting for 56.27%(1041/1802). The Global index was 0.198901 (P=0.000120), showing that there was a positive correlation between space and the incidence of brucellosis. The incidence rates in 2006,2007,2009 and 2012 and the space distribution appeared a positive correlation (P< 0.05) in Shandong province. The local index showed that there were 8 "High-High (HH)" clustering areas, which were proved to have statistical significance (P<0.05). Local indicators of spatial association (LISA) revealed that southwest and north districts of Shandong were highly clustered districts of brucellosis and the areas paralleled to the areas that having higher incidence rates. There were two spatial clustering areas in this study, one as the center of JuanCheng with radiation radius at 33.83 km, whose RR was 9.72 (P<0.05) and the other was the center of BinCheng with radiation radius at 62.78 km with RR as 4.99 (P<0.05). All the 8 HH counties (districts) were included in the two cluster regions.(3) Time series analysis:The incidence of brucellosis was increasing from 2004 to 2013. For the ARIMA (0,2,1) model, the white noise diagnostic check (χ2=5.58 P=0.35) for residuals obtained was revealed by the optimum goodness-of-fit test. The monthly incidences that fitted by ARIMA (0,2,1) model were closely consistent with the real incidence from 2004 to 2013. And forecasting incidences from January 2014 to December 2014 were respectively 0.101,0.118,0.143,0.166,0.160,0.172,0.169, 0.133,0.122,0.105,0.103 and 0.079 per100,000 population, with standard error 0.011-0.019 and mean absolute percentage error (MAPE) of 58.79%.2. Related factors of human brucellosisThe results showed that intake of incomplete cooked meat or taking food with unclean hands (OR=6.402,95%CI=2.029-20.198), animal-related occupatio ns (OR=1.846,95%CI=1.188-2.870), contacting with sheep (OR=4.871,95%CI= 3.059-.7.756), handling aborted animals (OR=2.258,95%CI=1.257-4.054), family member had brucellosis (OR=2.572,95%CI=1.054-6.273),as well as injured ski n exposed to animals (OR=1.912,95%CI=1.043-3.504) were the risk factors of Brucellosis. When exposed to animals, protective measures was with OR and 95%CI being 0.473 (0.293-0.764) and 0.623 (0.398-0.975) separately. There wer e synergistic interaction between lacks of protective measures and animal relate d occupation, family member had brucellosis,contacting with sheep, handling aborted animals,handling aborted animals and having skin injury and intake of incomplete cooked meat or holding food with unclean hands(P<0.05). The im munization coverage rate of domestic animals was 0.37%, that of cases was 0%, and that of controls was 0.18%.CONCLUSIONS(1) Incidence of brucellosis has been increasing year by year, and the epidemic areas have been expanding year by year in Shandong Province. The 46 to 55 year-old male farmers was susceptible of human brucellosis. The peak occurrence time of this disease was from March to August, namely spring and summer season. There is a positive spatial correlation of this disease including 8 high-high clusters. The cases were mainly in LuXi plains of south western Shandong and northern plains of northern Shandong, and two spatial clusters were found. The epidemic areas expanded from the north to central and from west to east. Cases were emerging in Yantai and Weihai, the east coast of Shandong, and the scope was expanding. ARIMA (0,2,1) was applied to simulate and predict Brucellosis well, and the model forecasted that the total incidence of brucellosis was 1.571/100,000 in 2014 obtained by, showing the epidemic of brucellosis continued to popular.(2) The results showed that intake of incomplete cooked meat or taking food with unclean hands, animal-related occupations, contacting with sheep, handling aborted animals, family member had brucellosis, as well as injured skin exposed to animals were the risk factors of Brucellosis. When exposed to animals, protective measures was with OR and 95%CI being 0.473 (0.293-0.764) and 0.623 (0.398-0.975) separately. There were synergistic interaction between lacks of protective measures and animal related occupation, family member had brucellosis, contacting with sheep, handling aborted animals,handling aborted animals and having skin injury and intake of incomplete cooked meat or holding food with unclean hands.