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Migrant population may have contributed to TB prevalence in Beijing
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Tuberculosis control measures in Beijing should take into account migrant populations living in the city, according to study results.
Researchers from China and Switzerland were able to distinguish between permanent residents and migrant populations because of a national residency registration system in place throughout China. Migrants must obtain a temporary residence permit to live in a region outside of their original zone. Migrants were defined as those who had been in Beijing for longer than a month but who still held permanent registration in their home area.
Results showed that migrants contributed both to the increasing prevalence of TB in Beijing and to the distribution of the disease throughout the city.
The results were published in Emerging Infectious Diseases.
Design
The study was conducted from 2000 through 2006 and the researchers used data from 2004 to 2006 to obtain results. There were 15,078 diagnosed cases of TB among permanent Beijing residents and 7,948 cases among migrants from Jan. 1, 2004 through Oct. 31, 2006.
The researchers divided the country into four regions based on economic and geographical factors: western, middle, eastern and two municipalities. Data indicated that migrants from the western, eastern and middle regions of the country were at a higher risk for TB than residents of urban areas. The infection rate in the poorer, more rural western zone of the country was about 1.7 times higher than in the eastern zone. Economic factors may play a role in this imbalance, according to the researchers.
A corollary study focusing on the economics of the issue also was conducted. Data from that study indicated that 80% of the families with a person infected with TB in China had a lower income than other families in the surrounding population.
Beijing
The researchers broke the capital city into 18 districts. They observed that certain districts with large migrant populations had increased rates of TB infection. There were no such clusters for permanent residents, and only one area had a slightly elevated number of infections among that population.
Though most of the migrant population lived in suburban districts, results indicated that there was a higher rate of infection among migrants in the four central districts of the city.
The researchers found that population density in the central districts may have caused the increased rate of infection. Approximately 20% of Beijing’s population lives in this area, which accounts for 0.50% of the surface area of the city. The researchers suggested that close quarters fostered high transmission rates.
Another possible explanation involved educational and occupational factors. Migrants working in the four central districts were employed in occupations that would bring them into regular contact with permanent residents. Migrants living in suburban areas were primarily university students, construction workers and technicians. These groups tended to form closed social groups and interacted with permanent residents less frequently.
Effective control measures were instituted to deal with the increase in TB transmission rates, and free therapy was offered to migrants with the disease, according to the researchers. – by Rob Volansky
For more information:
- Jia Z, Jia X, Liu Y, et al. Spatial analysis of tuberculosis cases in migrants and permanent residents, Beijing, 2000-2006. Emerg Infect Dis. 2008;14:1413-1419.