Testing HIV patients’ stool for tuberculosis (TB) may become an additional method for detecting TB, according to research recently published in The Lancet Microbe. Additionally, the test results show that using a stool sample resulted in a 45% TB detection rate in HIV patients with CD4 counts below 200 cells per cubic millimeter (200 cells/μl)—one of the criteria for an AIDS diagnosis.

The TB test used was Xpert MTB/Ultra, a molecular diagnostic test that traditionally relies on sputum samples. Xpert MTB/Ultra is currently an approved TB detection method in children with HIV, but it may eventually be approved as a test for adults as well, due to these results.

Sputum Leaves Something to be Desired

Sputum testing isn’t always the most reliable diagnostic source, the study explains. For example, patients may struggle to produce enough sputum for a TB test. The paucibacillary nature of the disease, meaning TB infections often have a low bacterial load, also results in false negative tests. Researchers hypothesized that a stool sample is a more readily available, noninvasive option that could solve accessibility issues, specifically the 50% diagnostic gap in HIV patients living in most low-income and middle-income countries.

A team of researchers led George William Kasule, Ph.D., first author and student at ISGlobal and the University of Barcelona, Spain, enrolled 677 HIV-positive patients over the age of 15 with suspected TB. The research took place between December 2021 and August 2024 at medical centers in Eswatini, Mozambique and Uganda. Patients provided stool, sputum and urine samples.

Stool samples accounted for 9% of overall TB detection when compared with sputum test results (6%) and urine test results (12%), the study shows.

“Stool is a noninvasive specimen, easy to collect, can be tested on existing platforms, contains viable organisms, is readily available even for repeat testing, and is safer to manipulate than sputum,” Kasule said in a news release. “The variety of samples obtained in this study allowed us to compare the sensitivity and specificity of the Stool Ultra test with a microbiological reference standard consisting of three WHO-recommended tests: TB-LAM in urine, liquid culture, and Xpert Ultra from sputum.”

A Worldwide Killer

Worldwide, TB is one of the leading causes of death for HIV patients, due to their weakened immune systems, according to the Centers for Disease Control and Prevention. Tuberculosis accounted for approximately 30% of the 690,000 AIDS-related deaths in the world in 2019, the World Health Organization adds. People living with HIV are also 14 times more likely to develop active TB than people without HIV. This is because TB is considered an opportunistic infection. An immune system weakened by HIV allows TB bacteria to enter, the first stage of which is called latent TB. Patients with latent TB do not feel sick and cannot spread it to someone else. Latent TB can lay dormant in the body for years. The second stage, TB disease, is contagious and causes the patient to feel sick as it multiplies in the body, according to the CDC.

“In conclusion, stool Ultra in adults with HIV substantially contributes to tuberculosis microbiological confirmation, yielding a high number of positive tuberculosis cases and identifying additional tuberculosis cases not detected using sputum and urine specimens only,” Kasule said. “These results suggest stool Ultra could be used as a diagnostic tuberculosis test among adults with HIV, especially in individuals with CD4 counts less than 200 cells per μL.”