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Keywords:

  • diagnosis;
  • drug susceptibility assay;
  • microscopy;
  • observational;
  • tuberculosis

Abstract

Background and objective

While commercial liquid culture techniques have emerged over 20 years ago, Ziehl–Neelsen (ZN) smear microscopy remains the primary method for diagnosis of tuberculosis (TB) in China because of cost considerations. The microscopic observation drug susceptibility (MODS) assay has been evaluated in different parts of the world to determine whether it can give comparable result to commercial liquid techniques. However, most reports detail evaluation of sputum specimens. This study evaluated the performance of MODS assay for detection of Mycobacterium tuberculosis in extrapulmonary specimens in a Chinese population.

Methods

A total of 173 samples, including pleural fluid (n = 112) and cerebrospinal fluid (CSF, n = 61) samples, were collected from patients suspected to have extrapulmonary TB and tested by ZN smear microscopy, Lowenstein–Jensen (LJ) culture and the MODS assay. Discordant results among MODS assay and the other two methods were resolved by 90-day follow-up evaluation for all suspected patients.

Results

The sensitivity of the MODS assay on pleural fluid and CSF samples was 20.5% and 37.5%, respectively, while the specificity of MODS assay on both types of samples approximated 100%. The median time to culture results for the MODS and LJ methods was 14 days, 32 days for pleural fluid, and 9 days and 31 days for CSF samples, respectively.

Conclusions

MODS assay is useful to diagnose extrapulmonary TB and may be an effective and affordable method in resource-limited countries.