Contamination Risk During the Use of Single Dose and Multi Dose Vials of Sterile Saline

Background: Aseptic procedures involving the use of sterile fluids and syringes are everyday practice in healthcare. Most of these procedures involve the transfer of sterile fluid from one compartment to another, and often between several compartments in a row. During such transfers there is a risk of contamination, which depends on the type and design of the devices used, the number of transfer steps and the quality of the aseptic technique applied. There is a need for better characterization and quantification of  these risks.

Objective: To quantify the risk of bacterial contamination during aspiration of sterile fluids from multidose and single dose vials.

Methods: Nurses were asked to aspirate the content of 20 ml single dose vials of saline into a syringe and thereafter inject the saline into a rubber stopped vial containing Tryptic soy broth (Group 1). In two other series, multidose vials with 50 ml or 100 ml of sterile saline were used for repeated aspirations for injections and for flushing of intravascular caheters as needed in a paediatric intensive care unit. Aspirations were either done via a permanently inserted dispensing spike (Group 2) or by perforations of the rubber stopper by a new needle and syringe for each aspiration(Group 3). After 24 hours, the volume of the remaining content was measured and submitted for culture. The number of aspitations over the 24 hour period were noted. Results:

	Group 1	Group 2	Group 3
Number of vials examined	253	226	200
Number of aspirations	253	1292	1198
Average number of aspirations	1	5.7 (range 1–26)	6,0 (range1-16)
Number of vials contaminated	4 (1.6 %)	3 (1.3 %)	6 (3.0 %)
Average contamination risk per aspiration	0.0158	0.0023	0.0050
Adjusted risk of contaminated aspiration *	0.0158	0.0089	0.0200

 * see conclusion
All contaminants were coagulase negative staphylococci or Micrococcus species.

Conclusions: Even though the level of contamination per vial was similar, the multidose vials had somewhat lower average risk of contamination per aspiration. However, contamination was measured only after the final aspiration, and since contamination may occur at any one of  the aspirations from multidose vials, the following aspirations will therefore likely be contaminated. An average of 5.7 and 6 .0 aspirations were done from the multidose vials respectively. Each contaminated vial would therefore theoretically result in an average of 2.85 (5.7/2) and 3.0 (6.0/2) aspirations respectively following the contamination event, largely eliminating the measured differences.