Risk factors for Cutibacterium acnes spinal implant-associated infection: a case-case-control study

The aim was to determine the characteristics of patients who developed Cutibacterium acnes spinal implant-associated infection (SIAI) and the associated risk factors.

We conducted two parallel case-control studies comparing 59 patients with SIAI caused by C. acnes (cases 1) and 93 patients with SIAI caused by other microorganisms (cases 2) diagnosed during 2010-2015 with 302 controls who underwent spinal instrumentation without subsequent infection.

Late-onset infections (median time to diagnosis, 843 days versus 23 days; p < 0.001) were more common in cases 1 than in cases 2. However, 20/59 (34%) of cases 1 occurred within the first 3 months after the index surgery. In addition, cases 1 were less likely to have fever (27%, 16/59 versus 58%, 54/93; p 0.001) or wound inflammation (39%, 23/59 versus 72%, 67/93; p < 0.001). Moreover, 24/59 (40%) of cases 1 presented with polymicrobial infections, and staphylococcal pathogens accounted for 22/24 (92%) of the co-infections. By comparing and contrasting the two multivariate risk models (cases 1 versus controls and cases 2 versus controls), the following factors associated with C. acnes SIAI development were identified: age <54 years (adjusted odds ratio (aOR) 2.43, 95% confidence interval (CI) 1.09-5.58, p 0.03), a body mass index <22 kg/m² (aOR 2.47, 95% CI 1.17-5.29, p 0.02), and thoracic instrumentation (aOR 16.1, 95% CI 7.57-37.0, p < 0.001).

Future therapeutic and prophylactic studies on C. acnes SIAI should focus on young, thin patients who undergo spinal instrumentation procedures involving the thoracic spine.