The effect of different head coverings on air-borne transmission of bacteria and particles in the surgical area was studied during 30 strictly standardized sham operations performed in a horizontal laminar air flow (LAF) unit. The operating team members wore disposable gowns plus either a non-sterile head covering consisting of a squire type disposable hood and triple laminar face mask, a sterilized helmet aspirator system or no head cover at all.

In the wound area both types of head cover resulted in low and comparable air (means of 8 and 4cfu/m³) and surface contamination (means of 69 and 126cfu/m²/h) rates. Omission of head-gear resulted in a three- to five-fold increase (P≥0.01− 0.001), depending on site sampled air contamination rate (mean of 22cfu/m³) whereas the bacterial sedimentation rate in the wound area increased about 60-fold (P≥0.0001). A proper head cover minimized the emission of apparently heavy particles that were not removed by the horizontal LAF and contained mainly streptococci, presumably of respiratory tract origin. Dust particle counts revealed no differences between the three experimental situations. No correlation between air and surface contamination rates or between air contamination and air particle counts was found.

We conclude that, from a bacteriological point of view, disposable hoods of squire type and face masks are equally as efficient as a helmet aspirator system and both will efficiently contain the substantial emission of bacteria-carrying droplets from the respiratory tract occurring when head cover is omitted. Finally, the use of bacterial air counts to assess surgical site surface contamination in horizontal LAF units must be seriously questioned.