Evidence for Tuberculosis in Individuals With Xpert Ultra "Trace" Sputum During Screening of High-Burden Communities

BACKGROUND

"Trace" results on Xpert MTB/RIF Ultra ("Ultra"; Cepheid) -a molecular diagnostic test for tuberculosis (TB)-are often interpreted as an indication for TB treatment, but may also represent detection of nonviable bacilli or analytical error. In community-screening settings where individual TB risk is low, there is limited guidance on how to interpret Ultra-trace results.

METHODS

We conducted systematic Ultra TB screening of adults and adolescents (≥15 years) in Kampala, Uganda, through door-to-door and event-based sputum collection. We enrolled individuals with trace-positive sputum for detailed clinical, radiographic, and microbiological (including 2 sputum cultures, repeat Ultra, and for people with HIV, urine lipoarabinomannan) evaluation, and compared those findings with similar evaluations in controls with Ultra-negative and Ultra-positive (non-trace) sputum.

RESULTS

Of 21 957 people screened with Ultra, 211 (1.0%) tested positive, including 96 (46% of positives) with trace results. Of 92 people enrolled with trace-positive sputum; 12% (11/92) were HIV-positive and 14% (13/92) had prior TB. The prevalence of TB among participants with trace-positive sputum results was 14% (13/92) by culture, 24% (22/92) using broader microbiological criteria, and 26% (24/92) after accounting for clinical diagnosis. The prevalence of cough and of abnormal chest computed tomography (CT) findings were 32% and 26%, respectively, if Ultra-negative; 34% and 54% if trace-positive/non-microbiologically confirmed; 72% and 95% if trace-positive/microbiologically confirmed; and 71% and 93% if Ultra-positive (more than trace).

CONCLUSIONS

Most individuals with trace-positive sputum in Ugandan communities did not have microbiologically confirmed TB but had more symptoms and chest CT abnormalities than people with Ultra-negative sputum.

Patient Experiences of Treatment Deferral for Evaluation and Monitoring after a Trace Xpert Ultra Result

Background

A "trace" result from the Xpert Ultra molecular TB test indicates Mycobacterium tuberculosis DNA detection but may not always signify TB disease. Little is known about the experiences of individuals with trace results who are not immediately treated.

Methods

We enrolled Ugandan adults and adolescents with trace Xpert Ultra sputum results, plus positive and negative controls, from community-screening and clinic settings. After a comprehensive TB evaluation, participants not recommended to start treatment immediately were closely monitored with interval reassessments. Surveys captured participants' perceptions and preferences related to their uncertain TB status at baseline and during follow-up.

Results

A total of 321 people with trace sputum (PWTS), 236 positive controls, and 279 negative controls were enrolled. A minority of PWTS thought they were highly likely to have or develop TB, and most reported low associated anxiety initially (258/321, 80%) and during follow-up. While about half (172/321, 54%) would have favored treatment at baseline if not in the study, those who remained untreated were less inclined toward treatment at six months. Participants generally preferred sensitive diagnostic tests, even with frequent false positives.

Conclusions

Deferring treatment for PWTS, with sufficient testing and monitoring, is acceptable to most patients.

The long-term risk of tuberculosis among individuals with Xpert Ultra "trace" screening results: a longitudinal follow-up study

Background

Systematic screening for tuberculosis using Xpert Ultra generates "trace" results of uncertain significance. Additional microbiological testing in this context is often negative, but individuals with trace results might have early disease or elevated risk of tuberculosis.

Methods

We screened for tuberculosis with Xpert Ultra in Uganda, enrolling individuals with trace-positive results and Ultra-negative controls. Participants without tuberculosis on extensive initial evaluation were followed, with repeat testing at 1, 3, and 6 months after trace results, and at 12 and 24 months for all participants. We estimated cumulative cause-specific hazards of incident tuberculosis, considering a definition of tuberculosis that included clinician judgment and one based strictly on microbiological results. We compared participants with Ultra-trace versus Ultra-negative sputum, and subgroups of participants with Ultra-trace sputum.

Findings

Of 129 participants with trace-positive screening results, 45 (35%) were recommended for treatment upon enrollment, and eight were lost to follow-up within three months. Of 76 remaining participants followed for median 697 (interquartile range 179-714) days, 20 (26%) were recommended for tuberculosis treatment. The cumulative hazard of clinician-defined incident tuberculosis was 26% (95% confidence interval: 14-38%) at one year and 35% (19-52%) at two years, versus 2% (0-5%) at two years for controls. Hazards were similar for microbiologically defined incident tuberculosis. Incident tuberculosis was strongly associated with abnormal baseline chest X-ray (hazard ratio 15.0 [3.4-65.1]) but not with baseline symptoms.

Interpretation

Individuals with trace-positive sputum during screening, particularly those with abnormal chest imaging, are at substantial risk of incident tuberculosis over the subsequent two years.

Funding

National Institutes of Health.