of new technologies compared with current methods, the performance testing and quality assurance needed for new technologies, the history and current responsibilities of the Supranational Reference Laboratory Network, and the contributions of FIND and the EXPAND-TB program to the scaling up of laboratory capacity in India.

DIAGNOSIS OF DRUG-RESISTANT TB1

As discussed earlier, the lack of diagnostic capacity has been a crucial barrier to the treatment of MDR TB. Today, however, at least 20 new diagnostic technologies are in different stages of development, and expanding laboratory capacity has become a global priority.

Ideally, DST should have at least the following characteristics:

  • high intra- and interlaboratory reproducibility;
  • short turnaround time;
  • ability to distinguish between high and low levels of resistance;
  • practicality and affordability;
  • minimal investment and costs for consumables;
  • minimal labor time; and
  • applicability to both first- and second-line drugs.

Culture methods, which are regarded as the gold standard, are still widely used today, but have limitations, including

  • long turnaround time;
  • failure to provide precise identification of species;
  • possibility of negative cultures for patients on treatment;
  • laborious testing procedures, including standardization of critical concentrations and establishment of appropriate inoculum size; and
  • issues concerning the stability of the drug in different culture media, the reliability of results, and quality assurance.

Several rapid assays measure resistance directly from clinical specimens. For example, a meta-analysis showed that the nitrate reductase assay (NRA) has a pooled sensitivity for detection of isoniazid and rifampicin resistance of 94 percent and 96 percent, respectively (Bwanga et al., 2009). The same analysis found a pooled sensitivity for the microscopic observation drug susceptibility (MODS) assay of 92 percent and 96 percent, respectively.

____________________

1 This section is based on the presentation of Camilla Rodrigues, Consultant Clinical Mi-crobiologist and Chair of Infection Control, Hinduja Hospital.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement