New tests could make the diagnosis of TB easier

Tuberculosis is difficult to detect
.
Diagnosis usually requires coughing up a sample of sputum from the lungs, which can be unpleasant, impractical, and even dangerous
.
But in a promising new study, a multinational team of researchers may have found another way to identify the bacterial disease
.

They found that having patients spit saliva into a cup and then put saliva into a commercial test box could detect the bacteria that cause tuberculosis — even though the test cassette was designed to use sputum
.

If more research confirms that this saliva bottle can be used reliably, the new approach could simplify widespread TB screening, especially in resource-limited clinics
.
This could strengthen efforts to detect and treat TB patients and help control the global spread of
this deadly infection.

"What we want to do in this study is try to improve standard diagnostic techniques," said senior author J.
said Lucian "Luke" Davis, Ph.
D.
, associate professor of epidemiology (microbial diseases) at the Yale School of Public Health and associate professor of medicine (lungs) at the Yale School of Medicine

He explained that the World Health Organization (WHO) has determined the need to detect tuberculosis
by means other than sputum.
To be effective, any such test would need to detect at least 90 percent of those infected
.

"In this project, we were able to reach that threshold," Davis said
.
He said the study provides an important proof of concept that this approach can work in a routine clinical setting, not just in
a specialized lab.

Another window into tuberculosis

In the current study, the researchers examined the accuracy of a next-generation molecular test bomb, called GeneXpert MTB/RIF Ultra (Xpert Ultra), produced
by Sunnyvale, California-based Cepheid.
The test is widely used worldwide to automatically detect the DNA
of Mycobacterium tuberculosis, which causes tuberculosis.

For sputum samples, this test is almost as sensitive
as the gold standard culture technique.
However, its role in
saliva has not been studied before.

The research team recruited clinical patients
known to have tuberculosis.
In each procedure, each participant first coughed up a sample of sputum, which the researchers confirmed the infection
through culture and pillbox testing.

Each person was then provided with saliva, which the team packed into another Xpert Ultra cartridge
.

The results are encouraging
.
Of the 78 tuberculosis patients confirmed by culture, 70 were detected with saliva, with a sensitivity of 90%.

Among people living with HIV, the test is less effective, with less than three-quarters of known TB cases
detected.
In contrast, 95% of cases
were detected in HIV-negative people.
(Because of altered immune responses, people with HIV carry fewer
TB bacteria than people without HIV.
) )

The study was intentionally small in order to understand whether this approach works
.
Researchers have yet to try to test saliva in children and non-coughing cough patients — both groups could benefit from
saliva testing.

What it means to have a simpler test

In 2020 alone, 1.
5 million people died from TB globally, the second fatality rate after COVID-19
.
Both diseases are easily airborne
.
The United Nations aims to end the TB epidemic
by 2030.
But there were 10 million new infections in 2020 alone, and to achieve this goal, vigorous efforts
in early detection are needed.

For years, sputum samples
have been needed for tuberculosis testing.
In fact, Davis said, TB researchers and clinicians have long been taught not to accept samples
that look like saliva.
This is because there may not be enough bacteria in the saliva to show up under a microscope or grow
in culture.

However, even with a good sputum sample, traditional diagnostic techniques can miss many cases
.
And phlegm has other disadvantages
.
A cough can infect people nearby, including health care workers
.
Davis explained that some people are unable to produce sputum as required, while others are ashamed
of the request.

But times are changing
.
Molecular diagnostic technology is widely used
.
After receiving World Health Organization endorsement in 2010, Xpert Ultra has sold millions of cartridges
in 130 countries for about $10 each.
Davis said Cepheids received an additional $10 per cartridge from the Global Health Initiative Unitaid, which means Cepheids receive about $20 per cartridge
.

Davis said the test was a "game-changer" and proved to be faster and more sensitive
than microscope-based TB diagnostics.

Evidence that this test may also work on saliva is welcome
.

"Some people feel a little uncomfortable, especially around (others)," said
lead author Patrick Baianyima.
He is an internationally trained scientist at Makerere University and a member of the Collaborative for Infectious Disease Research in Kampala, Uganda, both longtime partners
at the Yale School of Public Health.

When asked to provide a saliva sample, participants were more receptive
.

"In many cases, patients don't really need to be really far from other organs
when they provide specimens," he said.
"That's the
beauty of saliva.
"

Previous studies have explored the use of saliva in tuberculosis diagnosis
.
But the current study is the largest of its kind and the first to use widely available test equipment
.

After demonstrating that saliva testing is feasible, the researchers plan to test larger groups of patients, such as family members
, as next.
They also plan to see if procedural adjustments, such as asking people not to eat or brush their teeth until they provide samples, might improve test performance
.

The study was published online in
Microbiology Spectrum.
The study was funded
by the National Institutes of Health.