International Genetics and Genomics of Diseases: Tuberculosis Transmission

Modeling tuberculosis transmission flow

Background

China has the third largest number of TB cases in the world, and the average annual floating population in China is more than 200 million, the increasing floating population across regions has a tremendous potential for spreading infectious diseases, however, the role of increasing massive floating population in tuberculosis transmission is yet unclear in China.

Methods

29,667 tuberculosis flow data were derived from the new smear-positive pulmonary tuberculosis cases in China. Spatial variation of TB transmission was measured by geodetector q-statistic and spatial interaction model was used to model the tuberculosis flow and the regional socioeconomic factors.

Results

Tuberculosis transmission flow presented spatial heterogeneity. The Pearl River Delta in southern China and the Yangtze River Delta along China’s east coast presented as the largest destination and concentration areas of tuberculosis inflows. Socioeconomic factors were determinants of tuberculosis flow. Some impact factors showed different spatial associations with tuberculosis transmission flow. A 10% increase in per capita GDP was associated with 10.2% in 2010 or 2.1% in 2012 decrease in tuberculosis outflows from the provinces of origin, and 1.2% in 2010 or 0.5% increase in tuberculosis inflows to the destinations and 18.9% increase in intraprovincial flow in 2012. Per capita net income of rural households and per capita disposable income of urban households were positively associated with tuberculosis flows. A 10% increase in per capita net income corresponded to 14.0% in 2010 or 3.6% in 2012 increase in outflows from the origin, 44.2% in 2010 or 12.8% increase in inflows to the destinations and 47.9% increase in intraprovincial flows in 2012. Tuberculosis incidence had positive impacts on tuberculosis flows. A 10% increase in the number of tuberculosis cases corresponded to 2.2% in 2010 or 1.1% in 2012 increase in tuberculosis inflows to the destinations, 5.2% in 2010 or 2.0% in 2012 increase in outflows from the origins, 11.5% in 2010 or 2.2% in 2012 increase in intraprovincial flows.

Materials

Data

We used the database of 29,667 migrant TB cases from 2010 to 2012, which were diagnosed with new smear-positive pulmonary TB. Among them, 1,5640 migrant TB cases were confirmed in 2010 and 14,027 migrant TB cases in 2012. This data covered the 31 provinces of China, which have highly different geographical environments and socioeconomic conditions (Fig. 1). The data was provided by the Chinese Center for Disease Control and Prevention (CDC), and reported directly by a nationwide web-based Infectious Disease Reporting System (IDRS). Each case record in the dataset contained detailed information on age, sex, career, permanent residence, current residence, diagnosis month, results of smear microscopy diagnosis and so on.

Some studies have indicated that TB migration flows were influenced by various factors, such as income and social status, physical environments, working conditions, social environments, families, personal health practices and so on. Generally speaking, there are relationships and differences between generic population flow and TB flow.

On one hand, TB flow is part of the generic population flow, and TB migration flow refers to infected TB migrants in the floating population. There is a commonality between generic population flow and TB flow, as they are commonly affected by the different socio-economic and geographical environmental factors of the sending and receiving regions.

On the other hand, TB flow has its specificity compared with generic population flow. TB migration flows increase the risk of TB transmission from migrants to residents and amplify their harmfulness because of the dense population and active interactions with the migrating population. In addition, short and long-distance transmissions of infectious diseases are the result of the interaction between their own epidemiological mechanisms, and socioeconomic and environmental factors, and the complexity and variability of disease spread also require factors specific to TB transmission, such as the number of TB cases and TB incidence rate.