TB or not TB?
That has been the question for nearly 150 years, when Dr. Robert Koch first identified the rod-shaped bacterium that causes tuberculosis. This serious respiratory illness is currently the world's deadliest infectious disease, killing more than a million people a year.
The most common test to determine if someone has tuberculosis hasn't really changed since the late 1800s. The process relies on phlegm.
"It's a nasty substance," says Adithya Cattamanchi, a pulmonologist at UC Irvine. "No one likes it, right? You don't like to cough it up. Health workers don't like to work with it. It's difficult to work with in the lab because it's so viscous." In addition, not everyone can produce phlegm easily, including children, the elderly and those weakened by disease.
The phlegm is then examined under a microscope for the telltale tuberculosis bacteria. But the test is imperfect and imprecise. Sometimes patients are told they have TB when they don't. And about half the time, the test misses actual TB cases.
"So for a long time, we have been trying to make the diagnosis of tuberculosis easier, cheaper, and quicker," says Alfred Andama, a microbiologist at Makerere University College of Health Sciences in Uganda.
That desire was fulfilled last year when the Chinese company Pluslife announced a new tuberculosis test called the MiniDock MTB. It works by taking a sample of someone's phlegm or — if the patient is unable to produce phlegm — a mere tongue swab, heating and spinning it down, and then machine scanning it for DNA from the TB bacteria. It's faster than conventional tests and is portable, allowing health workers to use it in a wider variety of settings.
"It's cheaper than a microscope," says Cattamanchi, since swabs are easy to process. He explains that the device itself costs $300, and the fee per test is $3 to $4. "So it's more affordable, it's more accessible."
And it's more accurate, according to a new study that Cattamanchi, Andama and their colleagues published in the New England Journal of Medicine.
To conduct their study, the researchers enrolled almost 1,400 patients with TB symptoms at health centers across seven countries in Africa and Asia, including Uganda. Their results revealed that the new test was easy to use and met the World Health Organization's targets for accuracy, using either phlegm or the tongue swab. (The global health body had already recommended the test last month.)
"What we hope it means is that many more people will have access to high-quality TB testing," says Cattamanchi, who is also at the UCSF Center for Tuberculosis. That would help get people the care they urgently need while simultaneously reducing transmission of the bacterial disease.
"To have this low-cost option is, I think, really going to help countries scale up," he adds.
The perils of traditional testing
Over the years, Cattamanchi has spent time working at health centers across central and eastern Uganda. He's seen just how circuitous it can be for patients to find out they even have tuberculosis, a process that can take weeks or months.
"They may stop by a pharmacy," he says. "They're given some drugs for cough or for fever. But then the symptoms recur or get worse."
What's more, certain health facilities lack the ability to test for TB. "Many people are making three, four, five visits before they finally come to a health center where there is TB testing available," explains Cattamanchi.
Delays in testing and missed diagnoses allow the disease to tighten its grip, which can be disastrous. The patient would probably have become even sicker, says Andama. "And they keep transmitting the disease as they move between these different facilities," which puts others at risk of infection.
This is why early diagnosis — which leads to early treatment — is so crucial, and why the new MiniDock MTB came as such welcome news.
The new test followed from a burst of innovation during the pandemic, a period when swab-based testing for COVID-19 improved dramatically due to an infusion of effort and cash from researchers and industry.
Since then, some of those companies, including Pluslife, have pivoted the technology to tuberculosis.
Accurate and easy to use
Andama believes the implications are huge. "Most of the patients who are suspected to have TB could have access to TB testing," he says. "Detecting patients early, starting them on treatment early and following up to make sure they adhere to treatments makes a lot of improvement in their lives."
Lucica Ditiu is the executive director of the U.N. organization Stop TB Partnership. She wasn't involved in the research. "There is a lot of excitement in the world," she says. "We all think this is an amazing tool with two caveats."
First, she says that although the new test seems to work well for patients who've struggled with TB for some time, it may not catch the disease early on when there's a lower bacterial load. "For that type of work, we don't think this is the tool yet," she says. "Maybe it needs some improvement."
Second, Ditiu says the new test cannot distinguish between regular TB and the drug-resistant variety that doesn't respond to first-line antibiotics. Like the common microscope test, such a distinction requires an additional test to determine the proper treatment regimen.
However, catching and treating TB early reduces the likelihood that it will become resistant in the first place. Cattamanchi acknowledges that there's still a lot of work to do but he believes this test represents a real step forward.
"My hope honestly is that after more than 150 years, we finally get rid of using a microscope," he says. "And everyone who has TB symptoms is getting a high quality molecular test."
"And I think we're closer to that today than we've ever been before."
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