Hazards to laboratory staff in centrifuging screw-capped containers.

Reports on infectious diseases acquired by bacteriological laboratory staff from their work emphasize the risk of contracting tuberculosis by handling tuberculous specimens. Recent advances in the chemotherapy of tuberculosis have greatly increased the amount of bacteriology done in routine hospital laboratories, primary culture and then sensitivity tests being required where previously a direct positive smear of sputum was considered an adequate investigation. General protective measures, such as immunization of staff (who must be well trained in protective disciplines) and the provision of adequate accommodation, are obvious safeguards, but equally important is the re-examination of commonly used techniques to find out whether these are associated with any special risks. Quantitative studies made with air samplers have shown that there is considerable dispersal of bacteria into the air during many routine bacteriological operations (Wedum, 1953: Reitman and Wedum, 1956), and an outcome of this work has been the elimination of avoidable risky methods and the provision of screens and exhaust fans or safety cabinets to reduce unavoidable risks. These workers have studied the degree of air contamination during the technical operations concerned with centrifugation. They have shown that there is some aerial contamination during the filling of centrifuge tubes with cultures or infected material, during the removal of plugs or caps from centrifuge tubes, and when supernatant fluid is decanted from spun tubes. The atmosphere and apparatus are grossly contaminated when a tube breaks while being spun, but they consider that no risk is present during the normal running of a centrifuge. These findings have recently been summarized in an annotation in the Lancet (1956), which says " centrifuging a culture is safe enough -until the tube breaks." The present investigation was started because it was noticed that less than three months after the laboratory wall had been painted glossy white there were parallel horizontal dirty streaks about 7 in. above the bench on the wall behind an angle-centrifuge, and on the side of an incubator close to the centrifuge (Fig. 1). This centrifuge is used only for concentrating homogenized sputa for tubercle culture, and it is in use for about three hours each day. There is a similar centrifuge in the biochemistry department, mainly used for spinning urines, and we found similar streaks on the wall behind this apparatus. Both centrifuges have heads which take fouLr I oz. " universal " containers, and these widenecked bottles are always used for spinning sputa and urines, with their screw-on tops, fitted with rubber washers, tightly secured. The centrifuge heads are fitted with screw-on tightly fitting metal covers, and these are always used. It was decided to investigate the possibility that the contents of the universal containers were being sprayed around the laboratory during centrifuging, and the results prove that this has been happening.