| Tuberculosis (TB) is a public health problem which causes worldwide concern. According to the annual report from World Health Organization (WHO), there were about8,800,000new TB cases and1,450,000casualties in2010worldwide. In order to control tuberculosis, international agencies and countries have made strenuous efforts, especially in the past15years, DOTS chemotherapy (Directly Observed Treatment Short Course, DOTS) strategy was implemented in the world, and good results were observed. However, the increase of drug-resistant TB cases, HIV/AIDS pandemic, more frequent population movement, population aging, the world economic crisis and other factors bring new challenges to TB control efforts.In the recent two decades, migration has become an increasing concern for TB prevention and control programs all over the world. Global number of migrants in2010reached214million, with high-income countries in Europe, Asia and North America as the main destinations. According to the data of134countries and regions, immigration in high-income countries is one of the important factors that hinder the decreasing trend of TB incidence rate. The similar situation occurred in the major cities of China. Because of the accelerated urbanization process in China, there are labor surplus in rural areas, so a large number of farmers go to urban areas to find jobs, who are known as migrants. In2009the population of migrants in China reached211million. Considering that migrants in China are mainly from rural areas where the TB prevalence is higher (in2000TB prevalence was393/100000), while the destinations are urban areas with lower TB prevalence (in2000TB prevalence was211/100000), migrant population may change the TB situation in China’s major cities and bring new challenges for TB control. In the current study, we selected Shanghai as the field site to conduct a population-based epidemiological study, in order to explore the influence of migrant population in big cities on the TB epidemic, provide health workers and government policy-makers with theoretical basis of targeted TB prevention and control measures.As a prosperous metropolis, Shanghai attracts a large number of migrants. In2009the total population of Shanghai reached22,102,800, of which13.907million was local residents,8.1958million was migrants. According to the data of China Infectious Diseases Reporting System from the Shanghai Municipal Center for Disease Prevention and Control (CDC), we collected all the active TB cases among residents diagnosed during the period from January1,2000to December31,2009(44,670cases), and all the active TB cases among migrants diagnosed during the period from January1,2005to December31,2009(16,716cases). The incidence rate of active TB cases among residents decreased from40/100000in2000to28/100000in2005, and maintained for next4years. According to the results of multivariable analysis, higher proportion of young TB cases and middle-aged cases, higher proportion of smear-positive cases and higher proportion of TB cases who delayed in diagnosis explained the maintaining trend of TB incidence rate of residents. The incidence rate of active TB cases among migrants increased slowly during2005-2007, then decreased rapidly during2007-2009. According to the results of multivariable analysis, higher proportions of TB cases who had no treatment history and who received full supervision or strengthening-period supervision during treatment and higher proportion of TB cases who were diagnosed within30days and within90days were the reason why TB incidence among migrants decreased rapidly during2007-2009.(PART ONE)In order to explore deeply the impact of migrant population on TB spatial distribution and temporal trend, to clarify the incidence model of TB, we focused on the Songjiang District, Shanghai to do more detailed data collection and analysis. Songjiang District is located in the southwest of Shanghai, with total area of604.67km2. There is a national import and export processing industrial zones (including Chedun, Zhongshan and Xinqiao). During the period2006-2010, there were about500,000local residents each year in Songjiang District, while the migrant population increased sharply from620,000to more than1.4million. During the study period from Jan.2006to Dec.2010,2310active TB cases were diagnosed in Songjiang District, of which742(32.1%) cases were diagnosed among the local residents and1568(67.9%) cases were diagnosed among migrant population. The numbers of TB cases and incidence rates among local residents made no change during the5years:the number of new cases each year was about150, and the incidence maintained between25/100000-30/100000(P=0.256). The number of new TB cases among migrants reached300since2007, but the overall incidence showed a decreasing trend (P0.001). Better cure rate (OR=5.255,95%CI3.691-7.481) and a higher proportion of patients who accepted good management during treatment (OR=3.737,95%CI:2.907-4.805) was the main reason why TB incidence among migrants declined.According to the spatial analysis results, migrant cases and resident cases clustered in different regions and there was overlap in spatial clusters between migrant cases and all active TB cases, indicating that migrant cases explained mostly the formation of spatial cluster. Migrant population in industrial zone should be paid more attention in the TB prevention and control projects. There was a higher proportion of migrant cases in spatial clusters who lived in Shanghai for less than five years, especially those who lived in Shanghai for less than one year. What’s more, there was a higher proportion of migrant cases in spatial clusters who came from the Western Region. Smear positive tuberculosis incidence rate of the Western Region (199/100000) ranked first in China, followed by the Central Region(178/100000) and the Eastern Region(120/100000). This suggested that endogenous reactivation might play an important role among migrant TB cases. Migrant TB cases were likely to be infected by Mycobacterium tuberculosis (M.tb) in the original places, and reactivate into active TB in Shanghai. However, molecular epidemiological studies were needed to confirm this point, and to estimate the proportions of recent transmission and endogenous reactivation among TB cases in Songjiang District.In order to explore the transmission between migrants and local residents, and to clarify the TB model in Songjiang District, we started to collect M.tb strains from all culture positive cases and conducted genotype analysis from2008. During2008-20101426active TB cases were diagnosed (434were resident TB cases and992were migrant cases), and685(48.0%) cases were culture-positive(192were resident TB cases and493were migrant cases), of which517(75.5%) VNTR genotyping results were got successfully (165were resident TB cases and352were migrant cases). We found that133(25.7%) culture-positive patients belonged to48clusters, and the cluster rate was16.4%, indicating a lower proportion of recent transmission in all culture-positive TB cases. Proportions of cluster cases showed no significant difference (P-0.231) between local patients (48/165,29.1%) and migrant patients (85/352,24.1%). For the cluster cases, we carried out further investigation. However, due to frequent population movements, a large number of migrants went back home after diagnoed, and for the protection of privacy some cluster cases refused investigation, so finally we finished cluster investigation for a total of52cases (39.1%) in19clusters. We detected that11(21.2%) patients had epidemiological links with cases in the same clusters, of which two cases were family members, another two cases used to contact with the same TB cases, the other9cases were linked public places they often went to. What’s more, although we detected20mix clusters which contained both resident TB cases and migrant cases, we did not find evidence of transmission between resident cases and migrant cases during cluster investigation.In summary, we found that in Songjiang District, strateties for TB prevention and control among migrant population got good results, and TB incidence rate significantly decreased. Endogenous reactivation was the main mode of TB in Songjiang District, and migrant TB cases were likely to be infected by Mycobacterium tuberculosis in the original places, and reactivate into active TB in Shanghai. In Songjiang District the focus of TB prevention and control should be placed in migrants in the industrial area (mainly Chedun), especially in those who came to Shanghai for less than one year and who came from the Western Region. We recommended that high-risk population in Songjiang District should be screened for latent infection of M.tb, and those who got positive results should received isoniazid preventive therapy (IPT).(PART TWO)... |
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