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Mycobacterium tuberculosis is a highly infectious bacterium that is the causative agent of Tuberculosis (Murray, 2002, p.566). Tuberculosis is a global healthcare concern that has been declared an epidemic by the World Health Organization (WHO). It is estimated that approximately 30% of the world’s population has contracted the bacterium (Murray, 2002, p.568).
In Taiwan, tuberculosis is a leading cause of mortality even though it has been on the decline in the past few years. For example, in the year 2001, the infection rate was estimated at approximately 65 % for every 100, 000 people. Dou et al (2008) conducted a molecular epidemiologic study in Taipei involving 365 samples from patients that had contracted Mycobacterium tuberculosis (MTB).
Aim and relevance of the study to molecular epidemiology
The aim of the study was to define the prevalence of the various genotypes, drug resistance isolates and cluster patterns of Mycobacterium tuberculosis in Taipei in order to present information on the possible methods and routes of transmission (Dou et al, 2008, p.2). In addition, the researchers wanted to provide l information that would aid in the drafting of policies to control MTB infection (Dou et al, 2008, p.2).
Epidemiology is a field of science that studies the transmission and control of diseases. This study is relevant to molecular epidemiology because it offers hints on the best control practices of tuberculosis in highly populous regions, especially Taipei. It also studies the transmission of the bacterium in humans. The control of TB is difficult in densely populated areas because of the close contact between people and the availability of many reservoirs for the bacterium.
The study and the results
The researchers collected 356 samples from patients who had contracted MTB between the years 2002 and 2004 (Dou et al, 2008, p.2). The samples were obtained from patients at the Tri-Service General Hospital in Taipei, a hospital that handles many cases of TB in Taipei. The researchers ensured that the patients who participated in the study were culture positive and sputum microscopy positive. The research applied several methods to achieve the goals mentioned above.
The study involved the extraction of DNA form cultured cells that had been obtained from the patients. The colonies were suspended in 100-200 µl of distilled water and incubated at 85° C for a period of 30 minutes (Dou et al, 2008, p.2). The supernatant containing DNA was then isolated from the suspension and stored at -20° C. Another method used was spoligotyping. The isolates were spoligotyped and the resulting spoligotypes were analyzed using the Excel program (Dou et al, 2008, p.2).
The isolates also underwent PCR and MIRU analysis. The reagent system, Gibco-BRl was used to carry out PCR’s for the isolates (Dou et al, 2008, p.2). The primers used for amplification were selected based on the results of similar studies conducted earlier. The resultant PCR fragments underwent agarose gel electrophoresis for analysis. Other methods used to analyze the genotypes of MTB were TbDI analysis, drug resistance testing and NTF locus (Dou et al, 2008, p.3).
Molecular analysis of the samples revealed that Mycobacterium Tuberculosis caused almost all the TB cases in patients that participated in the study e. There was only one case of TB that was caused by Mycobacterium bovis. All samples underwent a drug resistance test and spoligotyping.
The results showed that 290 spoligotypes from the 356 isolates belonged to the same shared international types (SITs) (Dou et al, 2008, p.3). 44 of the remaining 66 isolates did not correspond to any type in the database. 47 spoligotypes were successfully identified and the most common was the Beijing spoligotype ST1 (Dou et al, 2008, p.2).
It was closely followed by the St50 spoligotype belonging to the Haarlem strain and then the ST19 spoligotype that belongs to the EA1_Manilla strain (Dou et al, 2008, p.2). The Beijing genotype was found in 187 isolates and it was the most rampant genotype. The study results also showed that patients who had contracted the Beijing family genotypes were much younger compared to patients with other family genotypes.
The MIRU-VNTR typing found 140n different patterns that included 36 clusters that were formed from 252 isolates (Dou et al, 2008, p.2). In addition, there were 104 distinct patterns formed from 104 isolates. 281 isolates were resistant to all the four drugs used in the study and the rest of the isolates were resistant to at least one drug. Only 2.8% of the total isolates were resistant to multiple drugs.
Public application of the information
Tuberculosis is a global health issue that has adverse effects on people. The information obtained from this study is useful in the public health sector because it can be used to counter the prevalence and transmission of TB. The methods used in the study such as spoligotyping and MIRU-NNTR genotyping are technologically advanced. They are useful in analyzing the transmission patterns and the genotype of MTB. This information is vital in the drafting and development of policies and strategies to control MTB infection.
The use of additional loci to type the genotype of MTB is important because it differentiates the various transmission patterns, clustering patterns and genetic relationships of different strains. This is important in developing the most appropriate control strategies. The study provides information that can be used to determine the prevalence of TB in Taipei and the most prevalent MTB genotypes, cluster patterns and transmission patterns. This information is vital in the control of Tuberculosis.
Dou, H., Tseng, F., Lin, C., Chang, J., Sun, J., Tsai, W., Lee, S., Su, I., and Lu, J. (2008). Molecular Epidemiology and Evolutionary Genetics of Mycobacterium tuberculosis in Taipei. BMC Infectious Diseases, 8(170), 1-12. doi: 10. 1186/1471-2334-8-170.
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Murray, A. (2002). Methodological Problems in the Molecular Epidemiology of Tuberculosis. American Journal of Epidemiology, 155(6), 565-571.