Three new rapid diagnostic tests for drug-resistant TB
9 September 2013
Three new diagnostic tests could each be used to successfully
diagnose drug resistance in tuberculosis (TB) patients in a quarter
of the time taken by the current method, according to new research.
The research, presented at the European Respiratory Society’s
Annual Congress in Barcelona, has provided evidence that each test
could be used as an effective alternative to standard testing,
increasing the possibilities available for clinicians.
Drug susceptibility tests are carried out in people with active
TB in order to identify which drugs the TB bacteria are sensitive or
resistant to. It is essential that these are identified as early as
possible so that the patient can be provided with the most effective
treatment and therefore the most rapid cure, and to prevent the
development of even more drug-resistant TB. This is particularly
important for patients with extremely-drug-resistant TB (XDR-TB),
who may have a short life expectancy if not treated properly.
Traditional methods of drug-susceptibility testing can take
anywhere between 21 days to 3 months because a sputum sample must
first be collected and cultured.
A new study carried out by researchers in the USA analysed three
- pyrosequencing, a DNA sequencing technique;
- the HAIN line probe test, a commercial test that detects
genetic mutations in the bacteria; and
- the microscopic observation drug susceptibility (MODS), test
which screens samples under the microscope.
The researchers investigated the effectiveness of the new tests
in over 1,000 patients in India, Moldova and South Africa. They
performed the standard drug susceptibility tests, alongside the
three new tests and evaluated drug resistance to five drugs:
isoniazid, rifampin, moxifloxacin, ofloxacin, amikacin, Capreomycin,
The results showed that the MODS test took 15 days to complete,
the pyrosequencing took 8 days to complete and the line probe assay
took 5 days. All three tests produced the same results as the
standard testing — 95-98% of the time for almost all the drugs.
Professor Antonino Catanzaro, from the University California, San
Diego, said: “Our findings suggest these three tests could provide a
quicker way to identify patients who need alternative treatment
regimens. This is very important and could potentially save lives as
well as help to curb the rise of drug resistant TB. There are
benefits and disadvantages to each test. For example, the MODS test,
although the slowest of the three new tests we looked at, is much
cheaper. It is important to have this range of options available so
that TB treatment programmes across the world can assess which
method is right for them including consideration of the financial
restrictions they work within.”