Yu et al. BMC Infectious Diseases (2020) 20:531 https://doi.org/10.1186/s12879-020-05249-3 RESEARCH ARTICLE Open Access Spatial-temporal analysis of tuberculosis in Chongqing, China 2011-2018 Ya Yu1,2†,BoWu1†, Chengguo Wu1, Qingya Wang1, Daiyu Hu1* and Wei Chen3* Abstract Background: China is a country with a high burden of pulmonary tuberculosis (PTB). Chongqing is in the southwest of China, where the notification rate of PTB ranks tenth in China. This study analyzed the temporal and spatial distribution characteristics of PTB in Chongqing in order to improve TB control measures. Methods: A spatial-temporal analysis has been performed based on the data of PTB from 2011 to 2018, which was extracted from the National Surveillance System. The effect of TB control was measured by variation trend of pathogenic positive PTB notification rate and total TB notification rate. Time series, spatial autonomic correlation and spatial-temporal scanning methods were used to identify the temporal trends and spatial patterns at county level. Results: A total of 188,528 cases were included in this study. A downward trend was observed in PTB between 2011 and 2018 in Chongqing. The peak of PTB notification occurred in late winter and early spring annually. By calculating * the value of Global Moran’s I and Local Getis’s Gi , we found that PTB was spatially clustered and some significant hot spots were detected in the southeast and northeast of Chongqing. One most likely cluster and three secondary clusters were identified by Kulldorff’s scan spatial-temporal Statistic. Conclusions: This study identified seasonal patterns and spatial-temporal clusters of PTB cases in Chongqing. Priorities should be given to southeast and northeast of Chongqing for better TB control. Keywords: Epidemiology, Spatial analysis, Tuberculosis Background China has reached the 2005 global tuberculosis control Tuberculosis (TB) is a chronic infectious disease caused targets [4]. It is the only country with a high TB burden by Mycobacterium tuberculosis (MTB). It is one of the that has made the achievements [5]. But TB remains a top 10 causes of death [1]. China contributed 9% of total major public health problem in China, especially in the cases in the world in 2017, ranking the second place relatively poor northern and western areas [6, 7]. after India [1]. In the 1990s, a TB control project, Chongqing is located in the southwest of China with including directly observed treatment and short-course 39 districts/counties, and 14 of them are national-level (DOTS) strategy, was implemented in 13 provinces of poor districts and counties [8]. In 2018, about 20,000 TB China [2]. Then the strategy had been expanded to the cases were reported in Chongqing with the overall noti- whole country by 2005 [3]. After more than 10 y efforts, fication rate of 73.4 cases per 100,000 population, which was higher than the average of the whole country [9]. A previous study of Chongqing pointed out that distribu- * Correspondence: [email protected]; [email protected] †Ya Yu and Bo Wu contributed equally to this work. tion of TB was uneven across the city [10], and a certain 1Chongqing Institute of Tuberculosis Control and Prevention, Chongqing, degree of seasonality was observed [11]. China In recent years, spatial-temporal analysis has been 3National Center for Tuberculosis Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, China widely used to describe the distribution characteristics Full list of author information is available at the end of the article and transmission patterns of tuberculosis in China [7, © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Yu et al. BMC Infectious Diseases (2020) 20:531 Page 2 of 12 12, 13] and other countries [14–18]. These studies dem- negative; and 3) PTB without pathogenic examination, onstrated that TB has a highly complex dynamics and is referring to those PTB patients who had slight symptom spatially heterogeneous at provincial, national, and inter- and could not cough up with sputum. national levels during certain periods of time [19]. Few Each enrolled case was geocoded by current address. studies have been conducted in Chongqing to explore Then them were matched to the county-level polygon the spatial epidemiology at the county level. In order to maps of the geographic information (Geographic data- improve TB control measures, we conducted Geograph- base from China CDC) at a 1:1,000,000 scale as the ical Information System (GIS) based spatial-temporal layer’s attribute table by the same identified number. scan statistic in Chongqing from 2011 to 2018. The longitude and latitude coordinates of the central point for each district and county were located though Methods the Google geocoding service and the toolbox of Geo- Study setting processing in ArcGIS v.10 (ESRI Inc., Redlands, CA, Chongqing is a mountainous city located in southwest USA). The coordinate information was used for spatial- China, with 27 districts and 12 counties. It covers an temporal analysis. This geocoding process has been area of 82,400 km2 [20], of which 76% are mountains, widely applied in previous studies [7, 19, 23, 24], and we 22% hills, 2% valleys and plains. The main stream of the used a similar approach. Yangtze River runs through the city from west to east, The annual population data of each administrative dis- with a flow of 665 km. In 2018, there are 31 million per- trict from 2011 to 2018 were obtained from the Chong- manent residents in Chongqing, of whom about 20 mil- qing Statistical Yearbook and the Basic Information lion were urban population, accounting for 65.5% of System for Disease Prevention and Control. total residents. The gross domestic product (GDP) per capita was RMB 65,933 Yuan in 2018 [21], which was Statistics analysis 1.9 times higher than that of 2011. Time series and descriptive analysis The epidemiological characteristics of TB cases were an- Data collection and management alyzed at provincial level. TB cases reported from 2011 The Chongqing TB surveillance data from January 2011 to 2018 were aggregated by age, gender, occupation and to December 2018 was extracted from the National date of onset for TB notification rate analysis. Compari- Surveillance System for Notifiable Infectious Disease, son between different demographic groups was carried which is established and operated by the Chinese Center out by Chi-square test or Fisher’s exact test. The trend for Disease Control and Prevention (CCDC). This surveil- of the notification rate was tested using Cochran- lance system covers all counties of 32 provinces, autono- Armitage test. All statistical analyses were performed mous regions and municipalities of China, and collects using SPSS 22.0 (SPSS Inc., Chicago, IL, USA). The dif- data of all TB cases reported by hospitals. We obtained ference was considered significant if P-value was less these TB data from Chongqing Institute of Tuberculosis than 0.05. Control and Prevention, and were permitted to use by The temporal patterns were examined by looking at CCDC. the onset month of all TB cases. The time series in- Each case contains demographic information as well as cluded 96 months from January 2011 to December 2018 medical information. Each case is identified by the and was examined using EXCEL2016. unique identity card (ID) number to avoid duplicate re- ports. In order to protect patients’ privacy, asterisk was Spatial autocorrelation analysis used to block the name and ID number of all cases when Spatial autocorrelation analysis is a spatial statistical the data were extracted. method that can reveal the regional structure of spatial The effect of TB control was measured by the vari- variables. It can verify whether an element attribute ation trend of pathogenic positive PTB notification rate value is associated with an attribute value at an adjacent and total TB notification rate. Pathogenic positive PTB space point. It mainly includes global autocorrelation includes smear positive (SS+) cases and smear negative analysis and local autocorrelation analysis. but culture positive (S-C+) cases. With the improvement Global Moran’s I values [25] calculated by ArcGIS v.10 of national infectious disease surveillance system, the ri- software (ESRI Inc., Redlands, CA, USA) was used to fampicin resistant tuberculosis (RR-TB) information has identify spatial autocorrelation and detect the spatial dis- been added to the system since July 1, 2017 [22], so tribution pattern of TB in Chongqing, China. The range pathogenic positive PTB in 2017 and 2018 also included of Moran I value is between − 1 and 1. A positive Moran RR-TB cases. The overall PTB included: 1) pathogenic I value indicates that a positive correlation exists, and positive PTB; 2) pathogenic negative PTB, referring to the larger the value, the more obvious the tendency to those PTB patients whose smear and culture were both cluster is, while a negative Moran I value indicates that a Yu et al.