Operating room S. aureus exposure has been directly linked to postoperative infections and is therefore an important target for infection prevention. Visible light (non-ultraviolet spectrum) at 405nm has been shown to be germicidal. We hypothesize that use of this light in operating rooms will reduce S. aureus transmission occurring within and between patients and reduce surgical site infections (SSIs). Visible light is safe for routine, continual exposure, and is less harmful than sunlight. We plan to install ambient, germicidal lighting in 4 operating rooms. This ambient light is not directly applied to patients (does not involve the surgical procedure lights). Patients will undergo surgery according to usual practice. We will conduct a case-control study where operating rooms with surgeries with the lights are matched to operating rooms with surgeries without lights.

In Aim 1, 4 OR-pairs will be observed each day over an anticipated 103 working days for the primary outcome of S. aureus transmission events over a total minimum study period of 5.2 months (103 working days).

Inclusion Criteria:

• Operating Rooms with and without the bactericidal lights where adult patients undergoing orthopedic, cardiothoracic, gynecology/oncology, and neurological surgery.

Exclusion Criteria:

• Operating Rooms with and without the bactericidal lights where pediatric, incarcerated, and/or pregnant patients undergoing surgery outside of the classifications above.