New Tuberculosis Test Is Faster and More Accurate

A simple and rapid new tuberculosis (TB) test is more sensitive, faster, and cheaper to perform than current culture-based tests.

The test, called microscopic-observation drug-susceptibility (MODS), was developed by scientists from the Johns Hopkins Bloomberg School of Public Health (Baltimore, MD, USA), the Imperial College London (UK), Universidad Peruana Cayetano Heredia, (Lima, Peru), and other institutions.

A study was carried out to determine the efficacy of the test. From April 2003 to July 2004, the study authors collected 3,760 sputum-saliva mixed with respiratory discharge-in order to complete sensitivity and susceptibility studies of the MODS test. All samples were decontaminated and then used for parallel MODS testing, as well as for two current gold standard TB tests: the Lowenstein-Jensen culture and automated mycobacterial culture, using the MBBacT system of Organon Technika (Cambridge, UK).

In order to test the samples using MODS, the scientists observed the cultures under an inverted light microscope for 40 days. The sensitivity of detecting TB was 97.8 % for MODS culture, 89 % for automated mycobacterial culture and 84 % for Lowenstein-Jensen culture. The median time for detection of TB was seven days for MODS culture, 13 days for automated mycobacterial culture, and 26 days for Lowenstein-Jensen culture.

The TB antibiotics isoniazid, rifampin, ethambutol, and streptomycin were added to the cultures in order to detect drug-resistant TB. Compared to standard culture reference methods, drug-resistant susceptibility agreement for MODS was 100% for rifampin, 97% for isoniazid, 99% for rifampin and isoniazid, (combined for multi-drug resistance), 95% for ethambutol, and 92% for streptomycin. MODS results were available, on average, in seven days, making them clinically relevant. Standard tests for TB antibiotics can take up to several months.

The MODS test relies on three principles: Mycobacterium tuberculosis grows faster in liquid medium than in solid medium; the bacteria grow in characteristic tangles or coils that can be seen microscopically in liquid medium; and the ability to incorporate drugs permits rapid and direct drug-susceptibility testing at the same time as the detection of bacterial growth.

The authors of the study, which was published in the October 12, 2006, issue of the New England Journal of Medicine, expect MODS will have a major impact in developing countries where resources are limited.



Related Links:
Johns Hopkins Bloomberg School of Public Health
Imperial College London
Universidad Peruana Cayetano Heredia