Determine TB –LAM Lateral Flow Assay, Does M. tuberculosis lineage influence its performance?

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Abstract Background The World Health Organization conditionally recommended the Determine lateral flow TB-LAM (LF-LAM) assay for tuberculosis diagnosis. The test is recommended for diagnosis and screening of active tuberculosis among HIV-infected individual’s adults with signs and symptoms of TB (pulmonary and/or extra pulmonary) with CD4 cell count less than or equal to 100 cells/mm3 or HIV-positive patients who are seriously ill, regardless of CD4 cell counts. However, the effect of MTB genetic diversity to the performance of LF-LAM remains unknown. We determined the perfomance of the against M. tuberculosis (MTB) lineages among HIV-positive individuals with pulmonary and/or MTB-bacteremia. Methods In a retrospective study, of 68 patients culture-positive for MTB, we used spoligotyping and/or MIRU-VNTR methods to determine the MTB-lineages. Patients 51 had both pulmonary and MTB-bacteremia and 17 patients had exclusively PTB. We compared the performance of LF-LAM against MTB-lineage in blood and sputum samples. LF-LAM performance was also analyzed in presence of mixed MTB-infection and patient CD4 cell count. Results The median age (interquartile range; IQR) of participants was 32 (30-35) and only sixty-six patients had CD4 results. The median (IQR) CD4 cell count/mm3 was 27(18-34). MTB-lineages in sputum were; CAS (L3) 17/68 (25%) and Euro-American-lineage (L4) 55/68 (75%) whereas in blood were L3 7/51 (13.7%) and L4 44/51 (86.3%). Among patients with TB-bacteraemia, LF-LAM was positive 100% for L3 and 32/44 (73%) for L4. LF-LAM was 100% positive among exclusively PTB patients with L3 and L4. The results did’not change by presence of mixed MTB-infection. Categroizing patients as CD4 <50 and ≥50 cell/mm3. All 100% of L3 strains remained with a positive LF-LAM test in both categories whereas 11 (68.7%) and 30 (82%) of the patients with CD >50 and ≤50 cells/mm3 respectively, with L4 had a positive LF-LAM test. Conclusions Our study show that L3 may have more specificity for LF-LAM assay than L4. Regional diversity in performance of LF-LAM assay may occur depending on the dorminat MTB lineage. Future studies on a large sample size with more MTB-lineage diversity are recommended.

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