Synovial Fluid Analysis in Melioidosis: Experiences from the Darwin Prospective Melioidosis Study

Melioidosis is a multisystem disease caused by the sapronotic soil bacterium Burkholderia pseudomallei. Septic arthritis (SA) can occur as either a primary or secondary focus and requires surgical management with prolonged antimicrobial treatment. We used the Darwin Prospective Melioidosis Study to identify patients with melioidosis and SA, filtered by culture confirmation of B. pseudomallei, and subsequently collected synovial fluid analysis, laboratory, clinical, and risk factor data. We identified 68 patients in total with a label of SA, of which 46 patients supplied 69 synovial fluid samples which were culture-positive. These most commonly came from the knee (61%) and ankle (16%), though half (54%) of the specimens were clotted and unable to undergo cell count. We found a median white cell count (WCC) of 63,000 × 10⁶ cells/L in B. pseudomallei culture-positive samples. There was a numerical, but non-significant, difference in median synovial fluid WCC when stratified by preceding antimicrobial use (90,000 × 10⁶ cells/L prior versus 27,800 × 10⁶ cells/L in samples taken post antimicrobial initiation; p = 0.053). One sample was B. pseudomallei culture-positive 32 days following antimicrobial initiation. The presence/absence of contiguous osteomyelitis did not alter synovial fluid white cell counts. These findings suggest that in cases of suspected melioidosis SA, it is not necessary to withhold empirical antimicrobial therapy while awaiting joint aspiration. Further research is needed to define the role of non-culture-based diagnostics in suspected melioidosis SA.