Cheap test slashes time taken to diagnose TB

An inexpensive portable diagnosis system can cut the time it takes to spot tuberculosis (TB) bacteria from weeks or months to less than half an hour, potentially helping doctors to catch infections before patients have time to unknowingly infect others.

The bacteria that cause TB, Mycobacterium tuberculosis, grow extremely slowly in the lab, so clinicians have few options for diagnosing the disease, says epidemiologist Jason Andrews at Stanford University in California.

They can either try to grow the bacteria from a sample — which can take up to two months — or look for them in a sputum sample smeared across a slide, a technique that can miss an infection 50% of the time.

A method called GeneXpert, made by Cepheid in Sunnyvale, California, and endorsed by the World Health Organization since 2010, can accurately detect M. tuberculosis DNA within a couple of hours, but it requires specialized equipment and trained personnel, making it impractical for rural areas or developing countries.

To speed up the process, chemist Jianghong Rao of Stanford and microbiologist Jeffrey Cirillo of Texas A&M Health Science Center in Bryan developed a chemical called CDG-3, which glows when it is broken down by an M. tuberculosis enzyme called BlaC. The researchers found that they could detect as few as ten bacteria in a millilitre sample.