Objective: to analyze the risk factors for the infection of Beijing genotype Mycobacterium tuberculosis (MTB) and the relationship to drug resistance and clinical symptoms.
Methods: sputum samples were collected from patients with pulmonary tuberculosis who were admitted to the hospital during July, 2007 to March, 2008. The sputum was cultured with L-J method, and then the bacterial DNA was isolated and genotyped with VNTR-7 (variable-number tandem repeats, VNTR) and RD105 deletion method respectively. The association between different genotypes and risk factors was analyzed.
Results: a hundred and sixteen clinical sputum isolates were obtained from 172 positive sputum cases. There were 112 isolates of MTB, and isolates of non-tuberculosis mycobacterium (NTM). Among the 97 isolates from Shanghai, Zhejiang and Jiangsu areas, Beijing genotype accounted for 86.6% (84/97), and non-Beijing genotype for 13.4% (13/97). The rates of MDR (multi-drug resistance), PDR (poly-drug resistance) and single drug resistance in Beijing genotype were not significantly higher than those in non-Beijing genotype. Among the risk factors, female gender, and CD(4)/CD(8)< 1 in patients with newly-treated tuberculosis, were associated with higher rate of Beijing genotype, chi(2) = 4.436, 4.494 and all P < 0.05, respectively. The Beijing genotype isolates were subdivided into 31 VNTR-7 types, and the distribution of quantity and resistance among different VNTR-7 genotypes was not even. A large number of MTB isolates (47.6%, 40/84) and drug resistant isolates (43.6%, 17/39) were among four VNTR-7 genotypes.
Conclusion: Beijing genotype is the most prevalent MTB in Shanghai, Zhejian and Jiangsu areas. Female gender and low CD(4)/CD(8) ratio in patients with newly-treated TB are risk factors for infecting Beijing genotype MTB, which may have no relationship with drug resistance and clinical symptoms.