Ventilation conditions and air-borne bacteria and particles in operating theatres: proposed safe economies.

Concentrations of air-borne bacteria and particles have been measured in turbulently ventilated operating theatres in full flow, half flow and zero flow conditions. Increased air-borne challenge produced by human activity and by mechanical cleaning procedures is demonstrated: die-away of this contamination is shown to be related to the ventilation rate. Ventilation can be reduced or turned off at night and during weekends, and cleaning can also be carried out, without increased risk of infection if full flow is restored one hour prior to preparation for surgery. Areas surrounding the theatres should remain at positive pressure with regard to the general hospital environment during low or no flow periods. The implementation of such energy-saving policies will substantially reduce theatre running costs without introducing infection hazards.