Will more sensitive diagnostics identify tuberculosis missed by clinicians? Evaluating Xpert MTB/RIF testing in...

Area of Science:

• Public Health
• Infectious Diseases
• Diagnostic Technologies

Background:

• Smear microscopy has limitations in diagnosing pulmonary tuberculosis (TB), especially in smear-negative cases.
• Accurate and timely diagnosis is crucial for effective TB control and treatment.
• Guatemala's national TB program sought to improve case detection through advanced diagnostics.

Purpose of the Study:

• To evaluate the impact of implementing Xpert (a nucleic acid amplification test) as a follow-on diagnostic for smear-negative individuals on overall pulmonary TB notifications.
• To assess the case detection yield and coverage of the Xpert intervention in Guatemala.

Main Methods:

• Genexpert systems were deployed in six Guatemalan departments, with Xpert testing offered to smear-negative patients.
• Analysis involved comparing quarterly TB notifications before and after the intervention using pre/post analysis and regression models.
• Project and national tuberculosis program (NTP) data were used to estimate potential yield at 100% testing coverage.

Main Results:

• Out of over 18,000 eligible smear-negative individuals, 39.6% were tested with Xpert, identifying 199 new cases (2.8% positivity).
• Smear-negative TB notifications increased by 85.6% (167 individuals), reaching an all-time high.
• Overall pulmonary TB notifications were 19% higher than predicted trends, with an estimated potential increase of 41% at full coverage.

Conclusions:

• The introduction of Xpert testing alone led to a substantial increase in pulmonary TB notifications.
• A significant number of TB cases in Guatemala were previously undiagnosed due to lack of bacteriological confirmation.
• Expanding access to sensitive TB diagnostics like Xpert can significantly improve TB case finding in similar settings.