title: [Primary drug-resistance is the main cause of drug-resistant tuberculosis].
abstract: OBJECTIVE
  To investigate the main cause of drug-resistant tuberculosis.
  
  
  METHODS
  Clinic isolates of Mycobacterium tuberculosis from 1996 to 2004 in Shanghai were analyzed and the proportion of isolates from new cases (the proxy of primary drug-resistance) and retreatment cases (the proxy of acquired drug-resistance) were calculated. Mycobacterial interspersed repetitive units (MIRU) genotyping was performed and analyzed on pairs of isolates of Mycobacterium tuberculosis from 16 recurrent patients with drug-resistant tuberculosis.
  
  
  RESULTS
  Of all 8 120 isolates of Mycobacterium tuberculosis from new cases, 707 isolates (8.7%) were drug resistant. Of all 610 isolates from retreatment cases, 150 isolates (24.6%) were drug resistant. Primary drug resistance accounted for 82.5% (707/857) of all drug resistant isolates. Based on the MIRU genotypes, 13 of all 16 recurrent drug-resistant patients were reinfected with new drug-resistant strain of Mycobacterium tuberculosis.
  
  
  CONCLUSIONS
  Primary drug-resistance is the main cause of drug-resistant tuberculosis.
authors: Department of Tuberculosis Disease Control, Shanghai Municipal Center for Disease Control and Prevention, Shanghai 200336, China.
authors: Jian
authors: J
authors: Mei
authors: Zhen
authors: Z
authors: Xue
authors: Xin
authors: X
authors: Shen
authors: Guo-miao
authors: GM
authors: Shen
authors: Xiao-hong
authors: XH
authors: Gui
authors: Mei
authors: M
authors: Shen
authors: Qian
authors: Q
authors: Gao