A method for excluding infectious agents from the site of an incision into the tissue of a patient. Air is the vicinity of the patient is filtered through an ionizing filter, such that any infectious agents in the air are electrically charged with a specified polarity. A region surrounding the site of the incision is thus characterized by an electrostatic charge of the same specified polarity as the infectious agents such that the infectious agents are repelled from the site of the incision. Infectious agents may be excluded from the site of an incision by creating a pressure field of air having a gradient along at least one path running from a zone including the incision to a neighboring zone so that air flows in the direction in the direction of decreasing pressure. A shield system with three layers may be provided, with the first layer substantially electrically insulating and adhering to the skin of the patient while an electrically conductive layer maintains an electrostatic charge of a specified polarity on the shield. An electrically insulating external layer prevents dissipation of the electrostatic charge. The shield system also has an ionizing air filter for charging any infectious agents with an electrical charge of the same specified polarity as the electrostatic charge of the shield for repelling infectious agents from the site of the incision.