Aerobic Bacterial Culture of Used Intravenous Fluid Bags Intended for Use as Urine Collection Reservoirs
Numerous studies have shown a relationship between indwelling urinary catheters and bacterial urinary tract infection. Some veterinary hospitals utilize stored, used intravenous (IV) fluid bags as part of the urine collection system. The authors cultured 95 such bags to see if they were potential sources of bacterial contamination. Forty-two unused IV bags were emptied of their contents for use as controls. Results indicated no aerobic bacterial growth in either group. The authors conclude that properly stored, used IV bags are unlikely sources of aerobic bacterial contamination when used in a urine collection system.
Introduction
Numerous studies in veterinary and human medicine have concluded that a relationship exists between indwelling urinary catheters and urinary tract infections (UTI).1–5 In one veterinary study, the incidence rate for UTI associated with indwelling urinary catheters was 32%.3 In people, 31% to 40% of nosocomial infections occur in the urinary tract, with 80% to 95% of them associated with indwelling urinary catheters.4,6
In addition to the duration of catheterization, the risk of developing UTI has also been correlated with the method of care.1,7 Guidelines to minimize risk include closed-catheter systems, aseptic catheter insertion, antibacterial cleansing of periurethral contamination before catheterization, antibacterial cleansing of the urethral-catheter junction, and sterile technique for catheter maintenance and irrigation.7,8 In people, simply using a closed system has been shown to decrease UTI incidence by approximately 20%.7 Without a closed collection system, 95% to 100% of human patients developed bacteriuria within 96 hours.7,9,10
Closed collection systems use purpose-built, sterile, urine collection bags and connection devices. Many definitions of open versus closed drainage systems exist, but this paper will use the following definitions: an open system is one in which the tubing can be disconnected at the collection bag; a closed system is a sterile, one-piece unit (that cannot become disconnected) with a drainage port at the bottom of the reservoir bag.10
Veterinary hospitals that do not use closed systems or sterile urine bags for collection may instead use intravenous (IV) fluid bags as urine collection reservoirs. The aim of the current study was to determine the prevalence of aerobic bacterial contamination in stored, previously used IV bags versus that of a control group of sterile IV bags that have been emptied of their contents. The authors hypothesized that used IV bags might contribute to bacterial contamination of the urine collection system if the prevalence of bacteria within the used IV bags was significantly higher than that within the control bags.
Materials and Methods
Study Group
The study group consisted of 95 previously used, 1-liter IV fluid bags that were stored in the hospital for future use as urine collection bags. None of these bags had contained dextrose. Nonsterile gloves were worn during all sampling procedures, collection, and handling. To ensure consistency, the primary investigator performed all of the sampling procedures. Samples were collected for 3 months to increase both the number of samples and the storage intervals for the used IV bags.
For each IV bag being sampled, the port of the IV bag was cleansed with a chlorhexidine solution for 4 to 5 minutes and then wiped with isopropyl alcohol. The isopropyl alcohol was allowed to dry before sampling. Single-use, sterile saline vials were used to draw 10 mL of saline solution into a sterile 20-gauge needle attached to a sterile 12-mL syringe. The 10 mL of saline was then injected into the cleansed port of the IV bag using the same 20-gauge needle and 12-mL syringe. The bag was gently swirled for 1 to 2 minutes while the needle and syringe remained within the port. The saline was then withdrawn using the same 12-mL syringe. Once the sample was extracted, the needle was changed before storing the sample in a sterile glass tube. The sterile glass tube was numbered and submitted for aerobic bacterial culture. The used IV bags were then marked with an “X” (before being returned to the storage bin for future use) to prevent the same bag from being tested more than once.
The date of initial use (if present on the IV bag) was recorded, along with the storage time before culture and the type of stopper. Some bags retained the IV-line spike as a stopper, with three-fourths of the IV line cut off and the remaining fourth tied into a knot on itself. The remaining bags had the IV spike completely removed and replaced by a sterile 1-mL syringe stopper.
Control Group
The control samples were obtained from 42 unused, sterile, 1-liter bags containing 0.9% sodium chloride. These control bags were cut with scissors at a corner distal to the sampling port and were emptied of their contents. The cut corner was then folded down on itself several times (so that the sampled saline would have no contact with the cut edge), and then it was clamped with hemostats. Samples were then immediately collected using the same methods as described for the study group, so that differences in collection technique would not affect the results.
Samples were initially collected by alternating between the study group and the control group. However, no growth was found on the first 31 control samples, so as a measure of consistency in technique, control sampling was thereafter limited to once every five to 10 study samples.
Aerobic Bacterial Culture
The samples were sent to a diagnostic laboratory for aerobic culture. One milliliter from each saline sample was transferred to a thioglycolate broth containing vitamin K and hemin, and then it was incubated for 18 to 24 hours at 37°C. The next day, the thioglycolate broth was subcultured to Columbia agar mixed with 5% sheep’s blood and then incubated at 37°C for a further 18 to 24 hours. Plates were examined for growth at 24 and 48 hours. All extra saline left over from the samples was held at 6°C in a walk-in cooler. Any positive samples were removed from cold storage and re-plated for confirmation.
Statistical Analysis
A sensitivity analysis was conducted before the study, using various estimates for sample size and proportion of positive and negative results. Confidence intervals (CI) of 95% were computed for the estimated proportions of positive samples. The actual results from the study and control samples were then used to estimate the exact population proportions.
Results
The results showed no bacterial growth on any of the 95 study samples or 42 control samples. This translates into an estimated proportion of zero positive study samples, with a 95% CI of 0.0% to 3.1% for all used IV bags. For the control group, the estimated positive proportion was also zero, with a 95% CI of 0.0% to 6.9% for all control IV bags.
Forty-three of the stored IV bags were dated, with the length of storage ranging from 0 to 17 days (median 3 days); 37 (86%) of these 43 samples were stored for ≤ 7 days. The remaining 52 stored IV bags were not dated. Of the stored IV bags, 61 retained the IV spike as a stopper, while the remaining 34 had a 1-mL syringe in place of the spike.
Discussion
The results showed no aerobic bacterial growth from any of the stored IV bag samples or control samples. The lack of growth in the control group indicated that the collection and sampling techniques did not contribute to bacterial contamination of the samples. It is possible that the method used to clean the port of the IV bag before sampling allowed chlorhexidine and alcohol to be entrailed into the bag, leading to false negative growth. However, the amount of chlorhexidine should have been negligible, because the alcohol was applied last and allowed to dry before needle insertion. Another potential limitation of the technique used is that the alcohol did not have a 2-minute contact time before drying, which might have resulted in incomplete disinfection. However, this would have resulted in false positive findings (with no bearing on negative results), so such a limitation should not have interfered with study results.
The authors conclude that previously used, properly stored IV bags are not a significant contributor to aerobic bacterial contamination when used as part of a urine collection system. In addition, the two types of stoppers used to store the bags in this study appeared to be equally effective in preventing bacterial contamination.
Even though the authors detected no bacterial growth in this study, the potential for the rare bag to be contaminated is always present. Based on 95 study samples, the 95% CI suggests a 0% to 3% chance of bacterial contamination when using a used IV bag as a collection reservoir; these percentages would be even lower in a larger sample size with no bacterial growth.
Based on the current study, storage of used IV bags for up to 1 week appears to be acceptable. However, the authors had information on length of storage for only 45% of samples from the study group, and only six of these were stored >1 week. Therefore, the relationship between bacterial contamination and storage time could not adequately be explored. Further studies specifically addressing longer storage times should be performed.
The authors did not perform anaerobic culture, which is a limitation of the current study. Anaerobes or other contaminants, such as yeast, could possibly be present in these stored IV bags. Future studies would be needed to search for these ancillary contaminants.
Results of the current study suggest that previously used, stored IV bags are unlikely sources of bacterial contamination when used as urine collection reservoirs. However, it must be emphasized that this type of setup is not technically a closed collection system, because the IV bag needs to be disconnected for emptying or for replacement. In human medicine, frequent disconnection of the reservoir bag from the collection system increases the likelihood of bacterial contamination.7,9,10 Future veterinary studies should compare the incidence of nosocomial UTI using used IV bags versus that using a sterile, closed urine collection system. These future studies must also seek to determine if the incidence of nosocomial UTI is affected by factors such as frequency of bag emptying, duration of attachment to the system before emptying, or frequency of bag replacement.
Conclusion
In this study, used IV bags that were properly stored for <7 days were not a source of aerobic bacterial contamination when used as part of a urine collection system.
Acknowledgments
The authors thank Mr. Jim zumBrunnen for help with statistical analysis.
