In 2011, 15 deep-seated Propionibacterium acnes infections were identified in patients following craniotomies in a hospital in the UK.

To describe the outbreak and report findings from the investigation undertaken in order to identify the source and risk factors and inform control measures.

Data were obtained from hospital clinical records and included patient and surgical variables. Cases were defined as patients with microbiologically confirmed deep or organ space surgical site infection (SSI) caused by P. acnes following craniotomy undertaken in 2011. Four controls per case were randomly selected from patients who had a craniotomy in 2011 but who did not develop any SSI. The relationship between infection and putative exposures was examined using multivariate regression techniques. Infection prevention procedures and the theatre environment were reviewed to assess compliance with existing standards.

Fifteen cases and 65 controls were recruited. Odds of infection were higher for those who had a dural implant inserted during their operation [adjusted odds ratio (aOR): 14.6; 95% confidence interval (CI): 0.95–∞] and for those who had alcohol/Betadine^®/chlorhexidine mix as a disinfectant (aOR: 7.9; 95% CI: 0.8–∞). Environmental investigations suggested that theatre ventilation systems delivered air exchange rates below the recommended standard.

There was a positive association between using dural implants and P. acnes infection. Infection may have been facilitated by inefficient use of skin disinfectant and environmental factors. Recommendations included ongoing surveillance, the use of chlorhexidine skin disinfectant, ensuring adequate air exchanges and appropriate use of doors in theatre to minimize air turbulence.