Open Access Research BMJ Open: first published as 10.1136/bmjopen-2013-004470 on 8 April 2014. Downloaded from Spatial analysis on human brucellosis incidence in mainland China: 2004–2010 Junhui Zhang,1,2 Fei Yin,1 Tao Zhang,1 Chao Yang,2 Xingyu Zhang,1 Zijian Feng,3 Xiaosong Li1 To cite: Zhang J, Yin F, ABSTRACT et al Strengths and limitations of this study Zhang T, . Spatial Objectives: China has experienced a sharply analysis on human increasing rate of human brucellosis in recent years. ▪ brucellosis incidence in Exploratory spatial data analysis methods and Effective spatial monitoring of human brucellosis mainland China: 2004–2010. the empirical Bayes smoothing technique were BMJ Open 2014;4:e004470. incidence is very important for successful used to analyse spatial patterns of incidence doi:10.1136/bmjopen-2013- implementation of control and prevention programmes. rates for human brucellosis at the county level in 004470 The purpose of this paper is to apply exploratory mainland China. Therefore, random variability spatial data analysis (ESDA) methods and the empirical was reduced, and greater stability of incidence Bayes (EB) smoothing technique to monitor county- ▸ Prepublication history for rates was provided mainly in small counties and this paper is available online. level incidence rates for human brucellosis in mainland true cluster areas with low false-positive rates To view these files please China from 2004 to 2010 by examining spatial performing especially well on outlier detection visit the journal online patterns. had a better chance of being detected. (http://dx.doi.org/10.1136/ Methods: ESDA methods were used to characterise ▪ The number of reported cases of human brucel- bmjopen-2013-004470). spatial patterns of EB smoothed incidence rates for losis obtained from the China Information human brucellosis based on county-level data obtained System for Disease Control and Prevention from the China Information System for Disease Control (CISDCP) system might be only part of the and Prevention (CISDCP) in mainland China from 2004 JZ and FY contributed actual incidence of human brucellosis across the equally. to 2010. country as human brucellosis is often under- Results: EB smoothed incidence rates for human reported or misdiagnosed. Received 12 November 2013 brucellosis were spatially dependent during 2004– ▪ Our analyses are based on county-level data. Revised 15 February 2014 2010. The local Moran test identified significantly high- Smaller spatial units might provide more http://bmjopen.bmj.com/ Accepted 20 March 2014 risk clusters of human brucellosis (all p values <0.01), location-specific information about the design which persisted during the 7-year study period. High- and implementation stages of public health risk counties were centred in the Inner Mongolia programmes. Autonomous Region and other Northern provinces (ie, Hebei, Shanxi, Jilin and Heilongjiang provinces) around the border with the Inner Mongolia Autonomous Region where animal husbandry was highly developed. husbandry activities, butchering and livestock 56 The number of high-risk counties increased from 25 in trading. Worldwide economic losses caused by brucellosis are extensive not only 2004 to 54 in 2010. on September 24, 2021 by guest. Protected copyright. Conclusions: ESDA methods and the EB smoothing in animal production but also in public technique can assist public health officials in health.1 Although brucellosis has been eradi- identifying high-risk areas. Allocating more resources cated from many industrialised countries, to high-risk areas is an effective way to reduce human new foci of disease appear continually, par- brucellosis incidence. ticularly in parts of Asia.7 fi 1 Brucellosis is classi ed as one of the class West China School of Public fi Health, Sichuan University, II national noti able diseases by the Centers Chengdu, People’s Republic for Disease Control and Prevention (CDC) of China and as a key disease in class II by the 2School of Public Health, INTRODUCTION Implement Detailed Rules of the By-law on Luzhou Medical College, Brucellosis, caused by Brucella species, is a Disease Prevention and Control of Livestock Luzhou, People’s Republic of 8 China zoonotic disease recognised as an emerging and Poultry in mainland China. The disease fi 8 3Chinese Center for Disease and re-emerging threat to public and veterin- was rst reported in China in 1905. Human 1 Control and Prevention, ary health. The disease is transmitted to brucellosis incidence was quite severe before Beijing, People’s Republic of humans by direct/indirect contact with the 1980s in the country; it decreased later China infected animals or through the consump- and remained at a low level. From 1995 to 2–4 Correspondence to tion of contaminated foods. People with 2001, the incidence of human brucellosis Professor Xiaosong Li; occupational exposure are at highest risk for increased rapidly and spread to more than [email protected] brucellosis, in particular those performing 10 provinces.8 In recent years, with the rapid Zhang J, Yin F, Zhang T, et al. BMJ Open 2014;4:e004470. doi:10.1136/bmjopen-2013-004470 1 Open Access BMJ Open: first published as 10.1136/bmjopen-2013-004470 on 8 April 2014. Downloaded from development of China’s animal husbandry, human bru- to conduct a geographic information system (GIS)-based cellosis incidence had increased sharply.9 Nationwide analysis of the spatial distribution of human brucellosis, surveillance data indicated that the total incidence rate the county-level polygon map at a 1:1000000 scale was of human brucellosis in mainland China increased from obtained.21 Demographic information from 2004 to 0.92 cases/100 000 people in 2004 to 2.62 cases/100 000 2010 was acquired from the National Bureau of Statistics people in 2010.10 Currently, human brucellosis is consid- of China. All human brucellosis cases were geocoded ered an important public health problem in mainland and matched to the county-level layers of the polygons China.11 by administrative code using the software Mapinfo The incidence rates of human brucellosis are not V.7.0.21 evenly distributed across regions in China.10 Awareness of the spatial patterns of human brucellosis is quite EB smoothing technique beneficial for the prevention and control of the disease. When raw rates derived from different counties across Exploratory spatial data analysis (ESDA) methods are the whole study area are applied to estimate the under- emerging as useful approaches to achieve this under- lying disease risk, differences in population size result in standing.12 ESDA is a set of techniques used to describe variance instability and spurious outliers. This is because and visualise spatial distributions, identify atypical loca- the rates observed in areas with small populations may tions or spatial outliers, discover patterns of spatial asso- be highly unstable in that the addition or deletion of ciation, clusters or hot spots, and suggest spatial regimes one or two cases can cause drastic changes in the or other forms of spatial heterogeneity.12 13 The observed values. Therefore, raw rates may not fully rep- methods can be applied by health officials to monitor resent the relative magnitude of the underlying risks if spatial variations in disease rates, which can assist health compared with other counties with a high population officials in designing more location-specific control and base. To overcome this problem, the EB smoothing tech- prevention programmes by taking into account global nique proposed by Clayton and Kaldor16 was applied to and local spatial influences.14 Measures of spatial auto- our brucellosis data. This method adjusts raw rates by correlation are at the core of ESDA methods.13 ESDA incorporating data from other neighbouring spatial methods and the empirical Bayes (EB) smoothing tech- units.22 Essentially, raw rates get ‘shrunk’ towards an nique are commonly combined to characterise spatial overall mean, which is an inverse function of the vari- – epidemiology of diseases.14 17 The EB smoothing tech- ance. Application of the EB smoothed incidence rate nique is used to reduce random variation and to provide not only provides better visualisation compared with the greater stability of rates mainly in small areas associated raw rate but also serves to find true outliers.23 with small populations.16 http://bmjopen.bmj.com/ The primary purpose of this paper is to apply ESDA Spatial autocorrelation analysis methods and the EB smoothing technique to monitor We performed spatial autocorrelation analysis in GeoDa county-level incidence rates for human brucellosis in V.0.9.5-i software.24 Global and local Moran’s I statistics mainland China from 2004 to 2010 by examining spatial were calculated. The global Moran’s I statistic was esti- patterns. Thus, we also identified the potential presence mated to assess the evidence of global spatial autocorrel- of clusters of the disease in mainland China to provide ation (clustering) of incidence rates over the study spatial guidance for future research. region.25 Anselin’s26 local Moran’s I (local indicators of spatial association (LISA)) statistic indicates the location on September 24, 2021 by guest. Protected copyright. of local clusters and spatial outliers. Spatial autocorrel- METHODS ation statistics for human brucellosis incidence rates Data source were calculated based on the assumption of constant Human brucellosis cases including 2872 counties in variance. The assumption might be violated when inci- mainland China from 2004 to 2010 were collected dence rates at the county level varied greatly across the through the Internet-based disease-reporting system whole study region.27 The EB smoothing technique was (China Information System for Disease Control and performed to adjust for this violation. The standardised Prevention, CISDCP), which was established in 2004 and first-order contiguity Queen neighbours were used as was more integrated, effective and reliable than the pre- the criteria for identifying neighbours in this paper. A vious case-reporting system.18 19 In mainland China, significant test was performed through the permutation human brucellosis is a reportable disease.