Tuberculosis (TB)
continues to be a leading cause of morbidity and mortality in developing
countries and India has the highest TB burden globally, accounting for 21% of
the global incidence and two- thirds of all cases in Southeast Asia. HIV and TB
co-infection form a lethal combination, each speeding up the other disease
progression thereby posing great public health challenge. Timely and accurate
diagnosis of TB is warranted for effective clinical management and preventing
further spread. However, still AFB smear microscopy remains the TB diagnostic
test of choice at most centres due to cheaper price and quick turn-around time,
though various studies show low sensitivity. Culture for TB remains the gold
standard though hampered by cumbersome procedures and the time delay. Automated
and semi-automated liquid based cultures are not affordable to TB patients in
developing nations. With the emerging threat of MDR-TB and extensively
drug-resistant TB (XDR-TB) strains, there arises the urgent need for a new,
inexpensive, rapid and sensitive diagnostic method for effective diagnosis of
TB and drug-resistant TB.
Microscopic
observation drug susceptibility (MODS), a simple assay developed and validated
in Lima, Peru. The assay was developed by making use of well-known properties
of Mycobacterium
tuberculosis that
the rate of growth in liquid medium is considerably quicker than that in solid
medium, and the morphology of M. tuberculosis in liquid culture is
characteristic and recognizable, consisting of "cords" and "tangles.
The MODS assay has been studied extensively and reported to be rapid and
accurate.
In a recently
published scientific article, Solomon S and colleagues from Chennai, India had
evaluated the suitability of the microscopic observation drug susceptibility
(MODS) assay, a novel assay for the diagnosis of TB and multi-drug-resistant
tuberculosis (MDR-TB) directly from sputum specimens, in the Indian setting.
This study involved a cross-sectional, blinded assessment of the MODS assay on
1036 suspected cases of pulmonary TB in HIV-positive and HIV-negative patients
against the radiometric method, BD-BACTEC TB 460 system.
Overall, the
performance of MODS assay in detecting MTB among TB suspects as shown by
sensitivity and specificity was 89.1% and 99.1% respectively. Further, in
detecting MDR-TB, MODS assay was 84.2% sensitive for those specimens reporting
MDR, 87% sensitivity for those specimens reporting INH mono-resistance, and
100% sensitive for specimens reporting RIF mono-resistance. The median time to
detection of TB in the MODS assay versus BACTEC was 9 versus 21 days (P<
0.001). By costing just about 5 to 10 times lesser than the automated
culture methods and way cheaper than the PCR based methods, the MODS assay has
the potential clinical utility as a simple and rapid method to be used in
resource-limited settings with high TB burden.
For further reading, click here.
Image courtesy: www.modsperu.org
Related Posts:
1. TB Beware
keywords: MODS, MOD, TB, MDRTB, MDR-TB, XDRTB, XDR-TB, Peru, Lima, David Moore, MODS assay, YRG CARE, GeneXpert, BACTEC, BD BACTEC TB 460, Suniti Solomon, Vignesh, Indian J Med Microbiol,
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