Transmission of Mycobacterium tuberculosis in China: A Population-Based Molecular Epidemiologic Study

MAJOR ARTICLE Transmission of Mycobacterium tuberculosis in China: A Population-Based Molecular Epidemiologic Study Chongguang Yang,1 Xin Shen,2 Ying Peng,3 Rushu Lan,4 Yuling Zhao,5 Bo Long,6 Tao Luo,1 Guomei Sun,1 Xia Li,1 Ke Qiao,1 Xiaohong Gui,2 Jie Wu,2 Jiying Xu,5 Fabin Li,3 Dingyue Li,6 Feiying Liu,4 Mei Shen,2 Jianjun Hong,7 Jian Mei,2,a Kathryn DeRiemer,8,a and Qian Gao1,a (See the Editorial Commentary by Arend and Soolingen on pages 228–32.) Background. Understanding the transmission of Mycobacterium tuberculosis is essential for the development of efficient tuberculosis control strategies. China has the second-largest tuberculosis burden in the world. Recent transmission and infection with M. tuberculosis, particularly drug-resistant strains, may account for many new tuberculosis cases. Methods. We performed a population-based molecular epidemiologic study of pulmonary tuberculosis in China during 1 July 2009 to 30 June 2012. We defined clusters as cases with identical variable number tandem repeat genotype patterns and identified the risk factors associated with clustering, by logistic regression. Relative transmission rates were estimated by the sputum smear status and drug susceptibility status of tuberculosis patients. Results. Among 2274 culture-positive tuberculosis patients with genotyped isolates, there were 705 (31.0%) tuberculosis patients in 287 clusters. Multidrug-resistant (MDR) tuberculosis (adjusted odds ratio [aOR], 1.86; 95% confidence interval [CI], 1.25–2.63) and infection with a Beijing family strain (aOR, 1.56; 95% CI, 1.23– 2.96) were associated with clustering. Eighty-four of 280 (30.0%) clusters had a putative source case that was sputum smear negative, and 30.6% of their secondary cases were attributed to transmission by sputum smear–negative patients. The relative transmission rate for sputum smear negative compared with sputum smear–positive patients was 0.89 (95% CI, .68–1.10), and was 1.51 (95% CI, 1.00–2.24) for MDR tuberculosis vs drug-susceptible tuberculosis. Conclusions. Recent transmission of M. tuberculosis, including MDR strains, contributes substantially to tuberculosis disease in China. Sputum smear–negative cases were responsible for at least 30% of the secondary cases. Interventions to reduce the transmission of M. tuberculosis should be implemented in China. Keywords. tuberculosis; molecular epidemiology; recent transmission; China. Received 27 October 2014; accepted 18 February 2015; electronically published 31 March 2015. a J. M., K. D., and Q. G. contributed equally to this work. Correspondence: Qian Gao, PhD, Key Laboratory of Medical Molecular Virology of Ministries of Education and Health, Shanghai Medical College, Fudan University, 138 Yi Xue Yuan Road, Shanghai, China, 200032 (). Clinical Infectious Diseases® 2015;61(2):219–27 © The Author 2015. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: . DOI: 10.1093/cid/civ255 Tuberculosis remains a major threat to global health, and is a leading cause of death in many developing countries. Infection with Mycobacterium tuberculosis leads to tuberculosis disease by 2 main mechanisms: infection and rapid progression to disease from a recent transmission event, and reactivation from latent tuberculosis due to a remote infection event and progression to disease [1–4]. It is important to distinguish between these 2 Transmission of M. tuberculosis in China • CID 2015:61 (15 July) • 219 1 Key Laboratory of Medical Molecular Virology of Ministries of Education and Health, Institutes of Biomedical Sciences and Institute of Medical Microbiology, Shanghai Medical College, Fudan University, 2Department of Tuberculosis Control, Shanghai Municipal Center for Disease Control and Prevention, 3Tuberculosis Control Center of Heilongjiang Province, Harbin, 4Guangxi Zhuang Autonomous Region Center for Disease Control and Prevention, Nanning, 5Henan Center for Disease Control and Prevention, Zhengdong New District, Zhengzhou, 6Sichuan Center for Disease Control and Prevention, Chengdu, and 7Department of Tuberculosis Control, Songjiang District Center for Disease Control and Prevention, Shanghai, People’s Republic of China; and 8School of Medicine, University of California, Davis METHODS were enrolled. The study protocol was approved by the institutional review board of the Institutes of Biomedical Sciences (protocol review No. 43), Fudan University. Laboratory Procedures For suspected tuberculosis, 3 sputum samples collected at different time points (spot, early morning, and night) were examined for acid-fast bacilli (AFB), and 2 of them were used for Lowenstein-Jensen culture. Sputum induction was used for patients who had trouble producing a sputum sample spontaneously. All of the M. tuberculosis isolates were sent to the provincial CDC for drug susceptibility testing to detect resistance to rifampin (RIF) and isoniazid (INH) using the proportion method on Lowenstein-Jensen medium at the following concentrations: RIF 40 µg/mL and INH 0.2 µg/mL [11]. Multidrug-resistant (MDR) tuberculosis was defined as resistance to at least INH and RIF. Bacterial genomic DNA was obtained from isolates by the boiled lysis method [12]. The Beijing genotype is the most prevalent family of M. tuberculosis strains in China [13].We used a set of variable number tandem repeats (VNTR), which was optimized for both Beijing strains and other strains in China, had high discriminatory power comparable to the IS6110–restriction fragment length polymorphism method [14], and included 4 hypervariable VNTR loci (VNTR3820, 1982, 3232, and 4120) that were in a consensus loci set for study recent transmission [14, 15]. We used BioNumerics software version 5.0 (Applied Maths, Belgium) to analyze the genotyping data. Tuberculosis cases whose M. tuberculosis strains had an identical genotypic pattern were considered a cluster, indicating recent transmission. Cases with a unique genotype pattern indicated reactivation of latent tuberculosis [2]. We restricted the cluster analyses within the local study population in each respective site. Crosscontamination may have occurred if ≥2 isolates from different patients in the same region were processed on the same day in the laboratory and shared the same genotype. Study Population We performed a population-based molecular epidemiologic study in 5 field sites in China from 1 July 2009 to 30 June 2012. In each of the 5 provinces, 1 county was selected as the study site (Supplementary Figure 1). The 5 sites represent geographical areas and populations with different tuberculosis burdens and socioeconomic levels based on China’s census system [10]. At each site, passive case finding was used to identify patients aged ≥15 years with suspected pulmonary tuberculosis with symptoms, including cough for at least 2 weeks, fever, chest pain, weight loss, night sweats, and abnormal ches (...truncated)