The value of clean zones and of transfer areas in operating suites was assessed by comparisons of the amounts of contamination on floors, trolleys and footwear in suites with and without a clean zone and a transfer area; counts of Clostridium welchii were used as an index of bacterial contamination introduced into the aseptic zone from outside.
The mean counts of Cl. welchii on contact plates from the wheels of trolleys used to convey patients from wards to the operating suite (67·9 ± 7·68 per plate) were significantly higher than those from theatre trolleys (i.e. those used only inside a theatre suite provided with a transfer area) (3·13 ± 0·47 per plate); mean counts of total bacteria were only slightly lower on the wheels of theatre trolleys than on those of hospital trolleys. Other surfaces of hospital trolleys showed counts similar to those found on theatre trolleys.
Contact plates from floors showed significantly lower counts of Cl. welchii in the aseptic zone and the clean zone than in the hospital corridor, the protective zone and (when present) the transfer area.
The mean counts per 100 cm2 of Cl. welchii were approximately the same on the floor of a theatre with a clean zone and a transfer area (0·83) as in one with a clean zone but no transfer area (0·5). Counts of total bacteria were higher in the latter. A suite with no clean zone or transfer area showed a higher mean count of Cl. welchii on contact plates from the aseptic zone (operating theatre) (20·5 ± 12·33 per 100 cm2). These higher levels of contamination were due to sporadic high counts of Cl. welchii found near the door of the theatre with no clean zone; in another theatre with no clean zone the level of Cl. welchii on the floor was not higher than that in the theatres with clean zones.
Theatres with plenum ventilation had lower mean counts of airborne Cl. welchii than those ventilated by windows: there was no significant difference in the levels of Cl. welchii on the floors of theatres with the two forms of ventilation.
On sampling with contact plates, theatre footwear yielded fewer total organisms, Staphylococcus aureus and Cl. welchii than outdoor shoes removed before entering the clean zone.
The hygienic value of transfer areas and clean zones is discussed. Bacteriological support could not be obtained for the former, but the latter appeared to contribute something to the cleanliness of the theatre by preventing heavy sporadic contamination.
We wish to thank Mr M. Wilkins for valuable assistance, the staff of the operating theatres for their co-operation and Alne Engineering Limited, 57 High Street, Henley-in-Arden, Solihull, for supplying disposable contact plates.