The aim of this prospective study was to use direct matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) to rapidly diagnose periprosthetic joint infections (PJIs).


 Positive blood cultures were analyzed using either direct or routine MALDI-TOF MS. Pathogen identification and the time to identification was recorded.  Direct and routine MALDI-TOF MS both detected 64 positive results (80%), compared to 47 (59%) by conventional swabs (p = 0.002).  Direct MALDI-TOF MS identified 85.3% of the gram-positive organisms and 92.3% of the gram-negative organisms.  No fungi were identified by direct MALDI-TOF MS. In 17 BCBs that were flagged positive, identification by direct MALDI-TOF MS failed.  Among the positive results in the direct MALDI-TOF MS group, Staphylococcus aureus accounted for 47%, followed by Staphylococcus epidermidis (17%), Escherichia coli (9%) and Klebsiella pneumoniae (9%).  The median time to microorganism identification was significantly shorter with direct MALDI-TOF MS (12.7 h, IQR: 8.9-19.6 h) than with routine MALDI-TOF MS (39.5 h, IQR: 22.8-46.0 h) or swabs (44.4 h, IQR: 27.2-72.6 h) (p < 0.0001).  In pairwise comparisons, there were significant differences in the time of microorganism identification between direct MALDI-TOF MS and routine MALDI-TOF MS (p < 0.0001) or swab culture (p < 0.0001).  There was no significant difference between routine MALDI-TOF MS and swab culture (p = 0.0268).


 Compared with current laboratory practice, direct MALDI-TOF MS shortened the time to microorganism identification and had superior results compared to conventional swabs, except for fungi. 
MALDI-TOF MS
Direct MALDI-TOF MS identified 85.3% of the gram-positive organisms and 92.3% of the gram-negative organisms.  No fungi were identified by direct MALDI-TOF MS. In 17 BCBs that were flagged positive, identification by direct MALDI-TOF MS failed.  Among the positive results in the direct MALDI-TOF MS group, Staphylococcus aureus accounted for 47%, followed by Staphylococcus epidermidis (17%), Escherichia coli (9%) and Klebsiella pneumoniae (9%).  The median time to microorganism identification was significantly shorter with direct MALDI-TOF MS (12.7 h, IQR: 8.9-19.6 h) than with routine MALDI-TOF MS (39.5 h, IQR: 22.8-46.0 h) or swabs (44.4 h, IQR: 27.2-72.6 h) (p < 0.0001).  In pairwise comparisons, there were significant differences in the time of microorganism identification between direct MALDI-TOF MS and routine MALDI-TOF MS (p < 0.0001) or swab culture (p < 0.0001).  Compared with current laboratory practice, direct MALDI-TOF MS shortened the time to microorganism identification and had superior results compared to conventional swabs, except for fungi. 
direct MALDI-TOF MS
Positive blood cultures were analyzed using either direct or routine MALDI-TOF MS. Pathogen identification and the time to identification was recorded.  Direct and routine MALDI-TOF MS both detected 64 positive results (80%), compared to 47 (59%) by conventional swabs (p = 0.002).  The median time to microorganism identification was significantly shorter with direct MALDI-TOF MS (12.7 h, IQR: 8.9-19.6 h) than with routine MALDI-TOF MS (39.5 h, IQR: 22.8-46.0 h) or swabs (44.4 h, IQR: 27.2-72.6 h) (p < 0.0001).  In pairwise comparisons, there were significant differences in the time of microorganism identification between direct MALDI-TOF MS and routine MALDI-TOF MS (p < 0.0001) or swab culture (p < 0.0001).  There was no significant difference between routine MALDI-TOF MS and swab culture (p = 0.0268).



routine MALDI-TOF MS