Tuberculosis Transmission and Risk Factors in a Chinese Antimony Mining Community
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INT J TUBERC LUNG DIS 20(1):57–62 Q 2016 The Union http://dx.doi.org/10.5588/ijtld.15.0215 Tuberculosis transmission and risk factors in a Chinese antimony mining community K-S. Chen,*† T. Liu,† R-R. Lin,‡ Y-P. Peng,§ G-C. Xiong§ *Key Laboratory of Medical Molecular Virology, Fudan University, Shanghai, †Department of Clinical Laboratory, First Affiliated Hospital of Nanchang University, Nanchang, ‡Department of Respiration, Wuning County People’s Hospital, Wuning, §Department of Clinical Laboratory, Jiangxi Provincial Chest Hospital, Nanchang, China SUMMARY SETTING: An antimony mine in Jiangxi Province, into 35 clusters. Estimated recent transmission of TB China. was 53.2% within the community. Patients who failed OBJECTIVE: To investigate the incidence of tuberculosis treatment were more likely to be in clusters (adjusted (TB) transmission and associated risk factors in a odds ratio [aOR] 0.03, 95%CI 2.12–6.89). Patients with Chinese antimony mining community. multiresistant isolates were more likely to have failed DESIGN: Retrospective cohort study treatment and to be in a cluster than those carrying a METHODS: The 15-locus mycobacterial interspersed susceptible strain (aOR 0.001, 95%CI 4.89–29.7). repetitive unit-variable number of tandem repeats CONCLUSIONS: Individuals who fail treatment are an (MIRU-VNTR15-China) method was used to determine important source of infection in TB transmission, and clustering of patients. A region of difference (RD105) multiresistant isolates are mostly responsible for this. TB deletion-targeted multiplex polymerase chain reaction control plans need to focus on treatment failure cases in was adopted to identify Beijing strains. Risk factors for the community. clustering were assessed. KEY WORDS: TB transmission; antimony; China RESULTS: Of 263 TB patients, 175 were distributed IN 2013, AN ESTIMATED 9 MILLION new cases of Jiangxi, located in Jiujiang, covers approximately tuberculosis (TB) were reported globally, more than 30 km2 and employs several thousand workers. half of whom (56%) are in South-East Asia and the Nearby farmers comprise the majority of miners Western Pacific; China accounts for 11% of total engaged in long-term antimony mining. Antimony cases.1 Concentrated efforts in China to control TB ore is usually processed in crowded, enclosed spaces transmission resulted in a sharp decrease in TB with a high density of dust, creating conditions 2 incidence between 1990 and 2010. Anti-tuberculosis favourable to the spread of TB.6 However, there are treatment has been less successful, however, in no publicly available data on TB transmission in the individuals exposed to silica in their work environ- antimony mining community. ments.3,4 As a result, they pose a challenge to TB The use of mycobacterial interspersed repetitive control. Antimony mining constitutes a setting in unit-variable number of tandem repeats (MIRU- which conditions might be expected to facilitate the VNTR) techniques have allowed a better under- transmission of TB. standing of TB transmission. When patients share Antimony (Stibium) is a valuable metal, with wide military and material application. Metallic the same MIRU-VNTR profile it is assumed that antimony is extracted from antimony ore, and recent transmission has occurred, while those with 7,8 during the subsequent smelting, workers are ex- unique isolates represent reactivation. In this posed to significant amounts of silica. China study, we adopted the MIRU-VNTR15-China method possesses the world’s largest deposits of antimony to identify potential epidemiological links. We also ore, and is the largest producer of refined antimo- collected and identified risk factors associated with ny.5 Antimony mines are distributed throughout such transmission, which provide a theoretical Guizhou, Hunan and Jiangxi Provinces and employ basis for future TB control activities in this nearly 100 000 people. The antimony mine in community. Correspondence to: Kaisen Chen, Department of Clinical Laboratory, First Affiliated Hospital of NanChang University, 17 Yongwaizhengjie, Nanchang 330006, China. Tel: (þ86) 189 7096 8159. Fax: (þ86) 791 8862 3153. e-mail: Chenks100@ 126.com Article submitted 7 March 2015. Final version accepted 22 July 2015. 58 The International Journal of Tuberculosis and Lung Disease STUDY POPULATION AND METHODS Estimation of minimum recent tuberculosis Study setting transmission rate The study was conducted in the Antimony Mineral The minimum recent transmission (n-1 method) was 12 Resource Development Company in Jiangxi Prov- estimated according to the following formula: rate ince, China, between January 2011 and December ¼ (number of clustered patients-number of clusters)/ 3 2013. All employees were male miners living in total number of patients 100%. nearby villages, except for a few foreign migrant Risk factors of clustered patients workers living in private accommodation. Since A cluster was defined as a group of two or more 2011, the local government departments have patients who shared the same MIRU-VNTR profile. required mining companies to provide regular health Patients whose isolates had more than one MIRU- checkups for miners. The local Chinese Center for VNTR profile were defined as ‘mixed infections’. They Disease Control and Prevention (CDC) offers TB were categorised according to the most common screening to individuals with symptoms as well as isolate, if this existed, and were excluded if it did not. control measures for local residents, including TB category was judged by clinical and/or CXR miners. All first-line anti-tuberculosis drugs are findings and self-reported history of TB. Recurrence routinely tested against isolated strains, and chest was considered any time after the end of treatment of radiography (CXR) services are available at all the previous episode. Treatment failure implied that times. All patients are treated under the DOTS patients had failed to respond to treatment or had only strategy under the supervision of a community experienced a transient response to treatment, and health worker. symptoms did not disappear even if the patients had taken anti-tuberculosis drugs for .6 months. Individ- Study population uals self-reported personal information such as age, Patients with at least one episode of culture-con- educational level, marital status, smoking status and firmed TB between January 2011 and December duration of employment as part of the health checkup. 2013 were eligible for the study, and were offered an Information on TB, such as drug resistance, CXR and additional free health checkup by the company. sputum smear results, was obtained from the local Enrolment was restricted to culture-confirmed TB CDC. patients who were currently employed by the mining company. Patients were excluded if they had extra- Data management and analysis pulmonary TB or atypical mycobacterial infection Clustering was analysed using the unweighted pair- with no concomitant pulmonary disease. The screen- group method with arithmetic averages (UPGMA). ing process is outlined in the Figure. Discrimination of locus combination was calculated using the Hunter-Gaston Discriminatory Index Laboratory methods (HGDI).13 The v2 test was used to analyse the Mycobacterial 16S rRNA gene sequencing and the correlation between the Beijing genotype and clusters. National Center for Biotechnology Information’s Univariate logistic regression modelling was used to Basic Local Alignment Search Tool (NCBI BLAST) calculate odds ratios (ORs) for factors associated with were employed to identify Mycobacterium tubercu- clustered and non-clustered patients. A multivariate losis complex.9 Beijing strains were discriminated by logistic regression analysis was used to control possible detecting the genomic deletion region of difference confounding factors, and age was included in the model (RD105) using multiplex polymerase chain reaction a priori. All other risk factors with a level of significance 10 (PCR). The MIRU-VNTR15-China method was of P , 0.1 were originally included. A forward stepwise adopted to genotype these strains. Genotyping approach was used in the analysis, and the interaction markers included MIRU10, MIRU16, MIRU23, terms were retained if they were significant. P , 0.05 MIRU26, MIRU27, MIRU39, MIRU40, Mtub21, was considered statistically significant. Mtub30, Mtub39, ETR-A, ETR-B, ETR-C, ETR-D and ETR-E. Primer design, amplification conditions Ethical considerations and the calculation of the number of repeats were The study was approved by the ethics committee of performed as reported in the literature.11 Drug the First Affiliated Hospital of Nanchang University, susceptibility testing (DST) to detect resistance to Nanchang, China (approval number: 2014036). All rifampicin (RMP), isoniazid (INH), ethambutol patients agreed to participate in the study, and all (EMB) and streptomycin (SM) was carried out on personal data were kept confidential. all M. tuberculosis isolates using the proportion method on Lowenstein-Jensen¨ media. Quality con- RESULTS trol was routinely performed during DST using H37Rv strains (American Type Culture Collection Of the 3543 employees, not all attended a health 27294). checkup at the local hospital; between January 2011 Molecular epidemiology of TB in China 59 interval [CI] 1.09–4.83, P ¼ 0.019) (see Appendix Table A).* Risk factors responsible for clustering are shown in Tables 1 and 2. Patients who failed treatment were more prone to clustering (Table 1); the study results indicate that 84.8% (28/33) of