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Evaluation of the microbial tightness of CSTDs

Currently, only few studies are available regarding the tightness of closed system transfer devices (CSTDs). The presented study deals with the evaluation of microbial tightness of CSTDs using airborne and touch contamination.

Nosocomial infections pose a major problem to healthcare system as they contribute to increased morbidity and mortality in hospitalised patients. According to the EPIC study, the most common bacterial pathogens for hospital acquired infections are Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa and coagulase-negative staphylococci.1 Moreover, viruses, parasites and fungi are isolated from patients suffering from nosocomial infections.

A patient can acquire an infection in three different ways:

  • The permanent or transient flora of the patient can cause an endogenous infection.
  • Another type of nosocomial infection is the exogenous cross-infection. According to the World Health Organization, in this case, microorganisms are transferred between patients through direct contact, aerosols and objects contaminated by patient’s flora and via medical staff.
  • Furthermore, the flora from the healthcare environment can cause an endemic or epidemic exogenous environmental infection. The latter type is caused by microorganisms which have well adapted to the hospital environment.2

Hospital-acquired infections are often associated with the use of medical devices. Open infusion systems and open drug transfer devices increase the risk for the entry of microorganisms which can lead to infections.

To minimise such infections, the National Institute for Occupational Safety and Health (NIOSH) requests the use of a closed system transfer device which is defined as follows3:

“A drug transfer device that mechanically prohibits the transfer of environmental contaminants into the system and the escape of hazardous drug or vapour concentrations outside the system”.

Therefore, in order to prevent nosocomial infections, it is necessary in addition to other hygiene measures to verify the microbial tightness of CSTDs.

Aims of the study

The first objective of this study was to evaluate the microbial tightness of a Safeflow valve integrated into a B Braun Mini-Spike® 2 Chemo V using airborne contamination. Mini-Spike® 2 Chemo V is a vented dispensing pin which is used for reconstitution and drug admixture. The second objective was to examine the microbial tightness after touch contamination. For this analysis, the Safeflow valve was used as a stand-alone medical device.

Safeflow valve airborne contamination analysis

The airborne contamination analysis was carried out with Bacillus subtilis (B. subtilis) spores, which were prepared and purified according to the laboratory standard method SOP 112 Bonn described in the doctoral thesis of Gebel in 1998.4

A B Braun Mini-Spike® 2 Chemo V was inserted into a vial containing 50ml of 0.9% sodium chloride solution. The spiked vial was placed together with five 10ml Luer Lock syringes, five Softa® Cloth CHX 2% wipes and five Combi-Stoppers in an exposure chamber.

A nebuliser containing a suspension of 4.8 x 105 cfu spores of B. subtilis per ml was used to generate an aerosol for one minute. The volume of B. subtilis suspension nebulised per minute is 0.278ml. This corresponds to 1.34 x 103 aerosolised spores of B. subtilis in the exposure chamber, which has a volume of 0.24 m3 (on average: 5.6 x 103 cfu/m3).

For an equal distribution of spores, the following procedure was carried out after two minutes. The Safeflow valve was disinfected with a Softa® Cloth CHX 2% wipe and left to air-dry for 15 seconds. Then a 10ml Luer Lock syringe was filled with 8ml of sodium chloride solution and closed with a Combi-Stopper. Thirty minutes later, B. subtilis suspension was nebulised once again but only for half a minute. The whole procedure starting from disinfection of the valve was repeated with the remaining four syringes.

The 0.9% sodium chloride solution from all syringes and the remaining fluid of 10ml in the vial was each filtered through a 0.45µm filter, which were incubated on tryptic soy agar at 37°C for 48 hours. Results were documented as cfu per 8ml and 10ml, respectively. The whole experiment was carried out three times. Three Mini-Spike® 2 Chemo V were tested per experiment.

  • Results

Table 1 shows that none of the tested Mini-Spike® 2 Chemo V showed transmission of B. subtilis spores through the valve after contamination of the chamber with 1.34 x 105 cfu of B. subtilis spores which corresponds to 5.6 x 103 cfu/m3 on average (95% confidence interval for microbial tightness: 66.4–100%).

Safeflow valve touch contamination analysis

The touch contamination analysis of the Safeflow valve was carried out with S. aureus.

S. aureus was prepared and purified according to EN 12353. A B Braun Intrafix® SafeSet administration set was inserted into a B Braun Ecoflac® plus IV solutions container with 500ml of 0.9% sodium chloride solution and the line was filled. An extension line (type “Heidelberger”) was connected to a single Safeflow valve and the end of the line was lead into a sterile graduated cylinder.

A suspension of 107 cfu/ml of S. aureus was used to contaminate the Safeflow valve. The volume of S. aureus suspension applied per valve was 10µl. This corresponds to 105 cfu of S. aureus on each valve. After a drying period of one hour the membrane of the Safeflow valve was disinfected with Softa® Cloth CHX 2% wipes and let to air-dry for 15 seconds. Following it was connected to the Luer lock of an Intrafix® SafeSet administration set.

The roller clamp of Intrafix® was opened and 80ml of the sodium chloride solution were transferred from Ecoflac® plus into the sterile glass. This procedure starting with the contamination of the valve was repeated four times. The collected infusate was filtered incubated (see experimental procedure for Mini-Spike® 2 Chemo V).

  • Results

As demonstrated in Table 2, all nine tested Safeflow systems did not show a contamination (95% confidence interval for microbial tightness: 66.4–100%).

B Braun Cyto-Set® and B Braun Cyto-Set® Mix  airborne contamination analysis

The third objective of this study was to evaluate the microbial tightness of the connection of B Braun Cyto-Set® and B Braun Cyto-Set® Mix through airborne contamination with spores of B. subtilis. The Cyto-Set® closed system is utilised for the preparation and application of cytostatic drugs.

Four B Braun Ecoflac® Plus IV solutions containers with 100ml of 0.9% sodium chloride solution and one B Braun Ecoflac® Plus IV solutions container with 500ml 0.9% sodium chloride solution were hung up in the exposure chamber. All four 100ml containers were spiked with Cyto-Set® Mix, the 500ml container was spiked with the main line Cyto-Set®. The end of the main line was drained out of the chamber into a sterile Erlenmeyer flask and all existing air vent-filters and clamps were closed. The nebulisation procedure was done as described for the testing of the Safeflow valve of the B Braun Mini-Spike® 2 Chemo V.

Two minutes after nebulisation, the first Cyto-Set® Mix was connected with the main line of Cyto-Set®. Then the clamp of this Cyto-Set® Mix was opened and the infusate was collected with a drip rate of 180 drops/min in a sterile Erlenmeyer flask. In the next step, the clamp of the main line was opened to rinse the system with 50ml 0.9% sodium chloride solution. The remaining three Cyto-Set® Mix were emptied in the same way.

Finally, the Erlenmeyer flask with the collected infusate of 600ml NaCl was emptied and examined for microbial contamination as explained above. One Cyto-Set® in combination with four Cyto-Set® Mix was tested per experiment.

  • Results

None of the tests with B Braun Cyto-Set® and B Braun Cyto-Set® Mix showed transmission of B. subtilis spores after contamination of the chamber with 1.17 x 105 cfu of B. subtilis spores which corresponds to 5.6 x 103 cfu/m3 on average (see Table 3).

Discussion and conclusions

The presented methods are suitable for evaluating the microbial tightness of the CSTDs as they simulate worst-case scenarios. The bioburden in ambient air of operating theatres and intensive care units ranges from 101 cfu/m3 to 102 cfu/m3 of air.5–7 The current study was carried out under exposure of 100-times higher concentrations of B. subtilis spores (on average: 5.6 x 103 cfu/m3).

The microbial concentration used for the touch contamination with S. aureus was 105-times higher than found on the fingertips of physician’s dominant hands, which carries on average 18.7 cfu/cm2 of aerobic bacteria.8 According to Pittet et al,9 intact areas of some patients’ skin can carry 100–106 cfu/cm2, which can serve as a source for microbial transmission onto the healthcare worker’s hands. That is why we decided to choose such a high concentration for the contamination of the Safeflow valve.

By means of these test methods, the microbial tightness of various medical devices such as container closure systems, air vent and prime stop filters in infusion sets and septums of intravenous catheters were also tested. These tested products showed, despite exposure to excessive air or surface contamination, good microbial tightness, providing they are applied according to instruction. Details of these examinations are intended for publication. In some cases, further investigations with greater numbers of samples are under consideration.

The content of this editorial was presented at the 35th International Symposium on Intensive Care and Emergency Medicine 2015 in Brussels. 


Jürgen Gebel
Sapuna Kuriakose
Barbara Grüter
Martin Exner
University of Bonn Hospital, Institute for Hygiene and Public Health, Germany

Conflict of interest

The experiments were carried out on behalf of B Braun Melsungen. The company did not have any influence on the evaluation of the results.


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