Objective:

To evaluate the diagnostic accuracy of the Active Melioidosis Detect Plus rapid diagnostic test (AMD-RDT) for detecting Burkholderia pseudomallei in throat swabs, using culture as the reference standard.

Approach:

• Study Design: A prospective diagnostic accuracy study using a 1:2 case-control design at microbiology laboratories in Cambodia and Laos.
• Specimen Selection: Throat swabs were collected from patients with suspected melioidosis. Each culture-positive specimen served as a case, with the next two consecutive culture-negative specimens selected as controls.
• Index Test: Stored aliquots underwent AMD-RDT testing, with results read after 15–20 minutes. Readers were not blinded to culture results.
• Statistical Analysis: Sensitivity, specificity, and likelihood ratios were calculated using culture as the reference standard. Researchers tested 114 specimens: 38 cases and 76 controls.

Key Findings:

• B. pseudomallei was cultured from 38 of 1451 throat swab specimens (2.6%).
• AMD-RDT sensitivity was 18.4% (95% CI, 9.2%–33.4%), and specificity was 100% (95% CI, 95.2%–100%).
• Positive AMD-RDT results occurred only in specimens positive on direct culture and were associated with greater growth abundance and culture positivity within 48 hours.
• The throat swab was the sole culture-positive specimen in 20 of 38 cases (52.6%); 9 of 38 (23.7%) required enrichment culture for detection.

Interpretation:

Despite high specificity, the AMD-RDT has inadequate sensitivity on throat swabs and cannot reliably exclude melioidosis. Low antigen burden likely contributes to its poor sensitivity.

Limitations:

• Delayed testing may have allowed degradation of the capsular polysaccharide targeted by the test, although accuracy was similar for testing within and after 4 days of specimen receipt.
• Using a single swab for both culture and AMD-RDT testing may have limited yield.
• Recruitment ended before the planned sample size of 234 specimens was reached.

Conclusion:

The findings do not support routine AMD-RDT use on throat swabs. Throat swabs and enrichment culture remain essential components of the diagnostic workup for melioidosis.