A $4 tongue swab test detects tuberculosis within 30 minutes
The portable test could help millions with limited access to health care
Mycobacterium tuberculosis bacteria (illustrated) causes tuberculosis. A new tongue swab test identifies an active infection in just 30 minutes with high accuracy, enhancing the chances of timely treatment.
KATERYNA KON/SCIENCE PHOTO LIBRARY/Getty Images
Diagnosing tuberculosis — the world’s most lethal infectious disease — with minimal training and without expensive laboratory infrastructure could now be a reality for millions.
A portable device using $4 tests detects tuberculosis, or TB, from tongue swabs within just 30 minutes, researchers report April 29 in the New England Journal of Medicine. The World Health Organization recommended the test in March, the first official endorsement for a TB test that can be used at community sites without laboratories and with minimal technical expertise.
The recommendation “opens a pathway to getting accurate molecular TB testing into the clinics where most people with TB actually show up,” says Adithya Cattamanchi, a pulmonologist at the University of California, Irvine.
Antibiotics can cure TB, but of the over 10 million people annually who suffer from the disease, over one-quarter remain undiagnosed or untreated. Smear microscopy, which has been used for around 150 years, tests phlegm to detect the type of bacteria that cause infections like TB. This test determines TB disease within 24 hours, but at least 1 in 4 people, including children, people with HIV and the elderly, cannot produce phlegm adequately. Smear microscopy also misses over 40 percent of TB cases. Due to microscopy’s limitations, WHO recommends diagnostics that generate copies of DNA traces from the bacterium causing TB. These diagnostics can detect disease within hours, but require expensive laboratory infrastructure.
In contrast, the portable device, called MiniDock MTB, is “designed to work anywhere: a rural clinic, a community health post, even outdoors,” optimizing roughly a decade of research on oral swabs for TB, Cattamanchi says. The entire setup works with a power bank or wall power, costs under $400 and requires minimal training.
A test with MiniDock, created by the Guangzhou, China–based company Pluslife Biotech, begins with collecting a tongue swab or phlegm sample. A machine spins and heats the tube containing the sample to release any genetic material. Then a worker pours the sample into a slot in a test card and loads it into the MiniDock testing platform to detect TB bacterial DNA in 12 to 25 minutes.
Cattamanchi and colleagues collected tongue swabs and phlegm samples from 1,380 people aged 12 or older from seven countries with high TB rates. MiniDock MTB successfully detected TB in 86 percent of TB-positive phlegm samples and 80 percent of TB-positive tongue swabs, meeting WHO’s accuracy goals. Its tests with phlegm outperformed smear microscopy by 24 percent, and were similar to standards for an expensive lab test.
But the inexpensive test has shortcomings. It was more accurate when detecting TB from phlegm compared with swabs. Cattamanchi notes that “accuracy isn’t the whole story” because for patients who cannot produce phlegm, a tongue swab is “the difference between getting a test and getting nothing.” Further, MiniDock MTB does not detect drug-resistant TB, but Pluslife is fast-tracking the development of such cards.
The test’s sensitivity declined if samples had few bacteria, which happens in the early stages of the disease. “This isn’t just a problem for tongue swab samples,” says epidemiologist Emily MacLean at the University of Sydney, who wasn’t involved in the study but is part of a group conducting TB screenings with MiniDock. “When there aren’t many bacteria present, it is just harder for tests to find a signal.”
MiniDock should be used in conjunction with other tests to improve the possibility of early TB detection, says epidemiologist Amira Roess at George Mason University College of Public Health in Fairfax, Va., who wasn’t part of the study.
Cattamanchi and colleagues are also testing TB diagnostics based on RNA patterns in blood, proteins and metabolites, to detect the disease without requiring any specimen from the airway. Tongue swab testing cannot replace every test, he says, but it can be a “tool that can get the right test to the right person at the right time.”
