Assay sensitivity and the interpretation of culture-based disc microbiology studies: a scoping review

Objective Studies examining the role of bacterial infection of intervertebral disc tissue in the aetiology of chronic low back pain with Modic changes have reported divergent findings. Because bacterial burden may be low, these findings may be influenced by differences in analytical sensitivity. This scoping review aimed to map the culture-based disc microbiology literature and examine how methodological features relevant to analytical sensitivity have been reported and applied across studies. Methods We conducted a scoping review of published culture-based studies of human intervertebral disc tissue microbiology. Studies were identified from the literature summarised by Gilligan et al. and by an updated PubMed search. We charted methodological features relevant to analytical sensitivity, including tissue sample mass, tissue disruption, dilution volume, plated fraction, anaerobic culture conditions, incubation duration, quantitative versus qualitative culture methods, prophylactic antibiotic reporting, and interpretation of positive findings. Where sufficient methodological detail was available, approximate lower limits of detection and quantitation were estimated for comparative purposes. Results The literature showed substantial methodological heterogeneity and frequent incomplete reporting of variables relevant to analytical sensitivity. Only a minority of studies reported sufficient detail to permit estimation of lower limits of detection or quantitation, and formal assay-performance characteristics were generally not reported. Considerable variation was observed in tissue sample mass, sample processing, dilution, plated fraction, anaerobic handling, incubation duration, quantitative reporting, and interpretive thresholds. These differences are likely to influence the ability of protocols to detect low-burden bacterial populations and may contribute to divergent interpretations of sterile cultures, low-count positive findings, and contamination versus low burden infection. Conclusions The published culture-based intervertebral disc microbiology literature for patients with low back pain is methodologically heterogeneous, and reporting of analytical sensitivity is often limited. Consideration of assay sensitivity may help contextualise divergent findings and should be incorporated into the design and reporting of future intervertebral disc microbiology studies. Additional well-described quantitative studies would strengthen the evidence base.