Impact of laboratory workflow optimization on initial acid-fast smear positivity and turnaround time in mycobacterial culture

Delays in processing automated liquid cultures after instrument positivity may postpone the microbiological confirmation and reporting of mycobacterial infections. This study evaluated whether introducing a centrifugation step after biological inactivation of MGIT 960-positive cultures was associated with higher acid-fast bacilli (AFB) smear positivity and shorter laboratory reporting and clinical follow-up intervals. This single-center retrospective before-and-after study included 156 cases with final positive mycobacterial culture reports at Peking Union Medical College Hospital: 66 before workflow optimization (January-April 2024) and 90 after implementation (May-August 2024). Following optimization, the initial AFB smear positivity rate among confirmed mycobacterial culture-positive cases increased from 42.42% (28/66) to 93.33% (84/90; P < 0.0001). All 84 initially AFB-positive cultures in the post-optimization group successfully underwent MPT64 antigen testing, while the proportion requiring Löwenstein-Jensen (LJ) subculture for further confirmation decreased from 57.58% (38/66) to 6.67% (6/90; P < 0.0001). Multivariable logistic regression showed that workflow optimization remained independently associated with initial AFB smear positivity (adjusted odds ratio, 22.64; 95% confidence interval, 8.18-62.67; P < 0.0001). The median interval from MGIT positivity to final reporting decreased from 7.21 to 1.50 days, and the median interval from specimen accession to final reporting decreased from 21.16 to 12.25 days (both P < 0.0001). The median interval from final reporting to subsequent clinical follow-up decreased from 45.35 to 18.65 days ( P = 0.0322). Introducing centrifugation after biological inactivation of MGIT 960-positive cultures was associated with higher initial AFB smear positivity, a greater proportion of cultures proceeding directly to MPT64 antigen testing without additional LJ subculture, and shorter laboratory reporting and clinical follow-up intervals. This simple workflow modification may improve the efficiency of culture-based mycobacterial diagnosis in laboratories using the MGIT 960 system. Not applicable.