Undetected TB May Be Lurking in U.S. Hospitals, Ultrasensitive Assay Suggests

A surprising number of at-risk U.S.-born patients might have forms of tuberculosis (TB) that are undetected by current diagnostic tests, studies of an ultrasensitive TB molecular assay suggested.

In testing 146 respiratory samples from a Boston safety-net hospital that were TB-negative according to conventional tests, the new assay found that 12.3% were positive for TB DNA. And in a clinical study of 101 primarily U.S.-born patients at the hospital, the assay turned up TB DNA in 16 patients (15.8%).

The positive numbers were far higher than expected, reported researchers led by Edward Jones-López, MD, of the University of Southern California in Los Angeles, in Nature Communications.

By contrast, among 50 traditionally tested TB-negative samples from a healthier control population at a nearby hospital with a lower burden of TB historically, only 2% tested positive.

None of the 16 TB DNA-positive patients had a clinical or microbiological TB diagnosis over a median follow-up of about 5 years, but the researchers believe they spotted a possible association between TB DNA positivity and acute chest syndrome in the subset of patients with sickle cell disease.

“We think we’re either detecting TB at a much earlier stage that may progress to classical TB, or we’re picking up a different kind of TB that is mostly inflammatory and not so much a bacteria-driven event,” Jones-López explained.

Regardless of the answer, “we still need to demonstrate that what we are detecting is indeed clinically relevant,” he cautioned. That will require larger studies combining treatment interventions and follow-up.

“By interrogating respiratory samples for the presence of [Mycobacterium] tuberculosis at a level of detection below that of currently available technologies, we detected M. tuberculosis DNA in an unexpectedly high proportion of hospitalized patients at a safety-net hospital,” Jones-López and colleagues wrote. The findings “may represent the initial description of a previously unsuspected variant of paucibacillary TB disease that is of yet uncertain clinical and public health relevance.”

Boston University researchers conducted three studies using the investigational Totally Optimized PCR (TOP) TB assay to detect M. tuberculosis DNA in discarded respiratory samples that were TB-negative according to conventional tests. The unexpectedly high TB prevalence in a study designed to test an assay’s accuracy caught the researchers off guard. “I frankly didn’t believe these data myself initially,” Jones-López told MedPage Today.

U.S. TB cases and case rates steadily slid from 2010 to 2019, dropped in 2020 at the start of the COVID-19 pandemic, and have risen since, according to the CDC. By 2025, the U.S. saw an estimated 7,858 TB cases among non-U.S.-born people and 2,252 cases among those born in the U.S. The nation’s rate of decline in TB incidence is too slow to eliminate TB by 2100.

New WHO guidelines recommend rapid molecular tests to diagnose TB. The TOP TB assay can detect M. tuberculosis DNA in patients with low bacterial loads who might be missed by sputum-based mycobacterial cultures or current molecular tests.

Among the 16 patients who were TB DNA positive in the longitudinal study at the safety-net hospital, 14 were U.S. born, and 12 were 50 years or older (mean 62 years). Sequencing results confirmed M. tuberculosis in all but one of the 16 TB DNA-positive patients. Standard mycobacterial culture tests were negative for TB in all but one of the TB DNA-positive patients.

Being TB DNA positive was associated with sickle cell disease (P=0.003) and asthma (P=0.05), and TB DNA-positive patients were also significantly more likely to be admitted to the hospital with sickle cell disease pain crisis (P=0.02) or chest pain (P=0.06). They were also more likely to have anemia (P=0.002), leukocytosis (P=0.06), and elevated direct bilirubin (P=0.01). Finally, all three patients diagnosed with acute chest syndrome and later discharged were TB DNA positive.

Study limitations included use of the research-only TOP TB assay, which lacks regulatory clearance, and the absence of an independent test to confirm results. Use of discarded respiratory samples may have affected specimen quality and risked sample contamination. Without tissue or autopsy results, the researchers couldn’t certify that M. tuberculosis directly contributed to symptoms, pathology, or death.