Prolonged outbreak of Staphylococcus aureus surgical site infection traced to a healthcare worker with psoriasis

Background: Meticillin-sensitive Staphylococcus aureus (MSSA) is a frequent cause of surgical site infection (SSI), but point-source outbreaks are rarely recognized. Aim: To describe an outbreak of MSSA SSI in a thoracic surgical unit. Methods: An outbreak investigation was started following two postoperative bacteraemias with MSSA resistant to fusidic acid (MSSA FusR). Patients with MSSA FusR were identified from microbiology records and through prospective case finding. Healthcare workers (HCWs) were screened. Isolates were characterized by phage typing, spa typing, pulsed-field gel electrophoresis and toxin gene profiling. A case-control study examined the association between one HCW with MSSA FusR and the patients involved in the outbreak. Findings: Nineteen patients were identified with MSSA FusR over 16 months. Four isolates were available for typing and all belonged to the same lineage. Seventy-six HCWs were screened. One was a carrier of the outbreak strain (a nurse with psoriasis). All 19 cases were exposed to this HCW compared with only 40/66 controls (P=0.003) and cases had a greater duration of exposure (P=0.00001, chi-squared for trend). Direct patient contact was documented in 15 cases. The outbreak was halted by thorough cleaning of the ward and removal of the HCW from clinical duty. Conclusion: The HCW with psoriasis was the source of this outbreak. MSSA FusR may be a marker for strains associated with skin conditions. HCWs with significant skin conditions may pose an infection risk in surgical settings. Recommendations are made for occupational health teams regarding screening of HCWs with dermatitis.