The performance and yield of tuberculosis testing algorithms using microscopy, chest x-ray, and Xpert MTB/RIF

Area of Science:

• Tuberculosis diagnostics
• Public health interventions
• Medical imaging in infectious diseases

Background:

• Smear microscopy has been the standard for TB diagnosis, but has limitations.
• Newer diagnostics like Xpert MTB/RIF (Xpert) and renewed interest in chest x-ray (CXR) offer alternatives.
• Programmatic data is crucial for understanding the impact of various TB testing strategies.

Purpose of the Study:

• To evaluate the impact of different diagnostic algorithms on TB detection rates.
• To compare testing strategies involving microscopy, Xpert, and CXR in a district hospital setting.
• To assess the yield, missed bacteriologically positive (Bac+) cases, and number of tests conducted.

Main Methods:

• Consecutive recruitment of patients with TB-related symptoms.
• Patients underwent smear microscopy, CXR, and Xpert testing.
• Six hypothetical diagnostic algorithms were analyzed for yield and efficiency.

Main Results:

• 17.3% of 929 patients were bacteriologically positive (Bac+) for TB.
• Smear microscopy detected 75.2% of Bac+ cases.
• CXR interpretation influenced Xpert testing reduction (31%-60%), and smear microscopy slightly reduced Xpert cartridge use but increased overall tests.

Conclusions:

• Xpert effectively identifies TB cases missed by smear microscopy.
• CXR significantly reduces the number of diagnostic tests required for presumptive TB patients.
• Further analysis of costs and standardized CXR interpretation is recommended for optimizing TB testing algorithms.