Infection control issues surrounding urine drainage bag design.

Dr Joanna Ford (R&D Officer) & Peter Phillips (Director) SMTL

Original article date: 22 January 2006

NOTE: the research in this paper has not been updated since 2006.


This paper highlights concerns over some designs of taps and connectors used in urine drainage bags (UDB). Specifically, it reviews information available concerning the potential infection risk of T-bar style taps and ridged connectors.

'T'-bars are sometimes found at the end of the 'outflow' tubing at the base of the urine drainage bag. The bar contains a hole that allows urine to flow through the tubing when pushed into position. This paper investigates whether the part of the bar that has been previously exposed to the external environment could make contact with the internal surface of the device when pushed into position and whether this could be a route for bacteria to enter the bag.

The surface of the connector which attaches to the catheter at the top of the bag can be smooth or ridged. There is also the potential for the ridges to harbour bacteria which would become dislodged during changeover of the bag, potentially introducing contamination into the catheter.

SMTL researched the evidence for these concerns, and this report reviews some of the literature currently published about urine drainage bag design and potential routes for infection.

Bacterial access into drained urine and/or the bladder

Urinary tract infection (UTI) occurs in many patients who are catheterised and numerous factors have been identified as having an impact (Platt et al., 1986). Some of these include contamination of the drainage bag or catheter tubing junction (Schaeffer 1986). One study (Tambyah et al., 1999) of almost 1500 catheterised patients identified routes of contamination by studying the type of bacteria found and the relative concentrations of bacteria sampled from the catheter and the drainage bag. For example, if bacteria were found in higher concentrations in the drainage bag than in other parts of the urinary system, the authors hypothesised that the source of contamination had derived from the bag. The results revealed that failure of the drainage system or contamination of the collection bag accounted for 34% of the infections detected. The other infections occurred upon insertion of the catheter or through entry of bacteria along the outside of the catheter tubing into the body. However, a criticism of this method is that one part of the catheter system may contain more bacteria than another because conditions have favoured faster colonisation, not because it was contaminated first. Another similar study involving 90 catheterised patients (Pien and Landers 1983) reported that out of 21 patients who developed bacteriuria, only one was likely to have caught it from an infected drainage bag (as the bacteria was detected in the bag before the catheter).

Evidence for the perceived risks

SMTL contacted a number of infection control nurses and medical device companies with regards to these issues. The infection control nurses that responded stated that smooth connectors between the catheter and the drainage bag were considered better from an infection control point of view as ridges had the potential to harbour bacteria. However, no one could provide evidence to indicate that this actually occurred clinically. Smooth connectors are considered by some nurses to possess a better grip and connection compared with ridged connectors (personal communication with continence nurse). With regards to the outlet tap at the base of the urine drainage bags, one infection control nurse stated that the T-bar design should be discouraged as they could allow organisms to enter the bag from external sources, such as dirty hands. However, another stated that T-bars were more secure than other types (such as the Flip-valves, which could be opened accidentally).

Impact of device design on infection rates

The importance of urine drainage system design has been recognised for some time. Some investigators suggest that junctions in the drainage systems (such as connectors and drainage valves) are the most significant factors in bladder infections (Sabanathan et al., 1985).

The literature review carried out for this report did not identify any published studies where different types of catheter/bag connectors (such as smooth or ridged) were compared. However, some studies have compared a simple closed drainage system (possessing a connector between the catheter and the drainage bag) with a pre-connected version (Will et al., 1993, DeGroot-Kosolcharoen et al., 1988). Their results indicated that the additional features were no more effective in preventing infection than a conventional system. As well as incidence of infection, one of the studies (DeGroot-Kosolcharoen et al., 1988) showed that the onset time for infection was also similar between the 2 groups.

Another randomised controlled study (Classen et al., 1991) compared episodes of bacteriuria between 2 groups of catheterised patients. Patients in one group had a silicon catheter pre-connected to a drainage bag by a red plastic seal and the other had a hydrophilic polymer-coated catheter, also pre-connected to a drainage bag but with the addition of daily disinfection of the drainage bag outflow tube and the catheter (external to the urethra). Results revealed that infection rates were very similar between the two groups, both of which the authors stated were unusually low. This could mean that the sealed catheter junction was the most significant infection control measure. However, this cannot be confirmed because a control group (with a non-sealed catheter junction) was not included. It would have been useful to compare the same type of catheter, where one utilised the sealed catheter junction and the other did not. The authors concluded that the addition of disinfection measures (of the catheter and outflow tap) in the second group did not reduce infection rates compared with the other non-disinfected group.

There is a small amount of research on infection control issues related to drainage bag outlet taps. One study filled 7 models of leg and drainage bags with E coli solution, drained the bag and swabbed the inner and outer surfaces of the spout and the tap following decontamination. Swab samples were cultured to identify contamination (measured fairly coarsely by grading the contamination as light, moderate or heavy) (Wilson and Coates, 1996). Five systems had contamination on the internal surface of the outlet port. The two 'T' bar systems had 'moderate' contamination but three of the drainage bags with other outlet tap designs had 'heavy' contamination on the internal surface.

Valves such as the Bard Flip-Flo (Addison 1999) have recently been used at the end of Foley catheters which allows the intermittent emptying of the bladder, rather than continuous drainage into a leg or night drainage bag. The flip-flo valves can also connect the catheter to the drainage bag and some outlets from drainage bags possess a 'flip-flo' style of valve. Some users interviewed by SMTL have said that they prefer a 'flip-flo' style valve to a more conventional 'T' bar because the bar can be knocked by patients which can open the tube, whereas the 'flip-flo'-style valves lie flat and cannot be readily knocked out of position. However, others stated that T-bars appeared to be more secure.

One study compared two urine drainage systems: a catheter and catheter-valve system (no bag) with a conventional drainage bag system (Wilson et al., 1997). No significant difference in infection rate was detected between the two groups. However, a couple of cases of valve blockage caused by the build up of sediment from the urine were reported during the study.

Design versus handling

Many bladder infections have been attributed to poor technique (Pien and Landers 1983) rather than design which reiterates the importance of training in this area. The authors of one of the studies (DeGroot-Kosolcharoen et al, 1988) felt that catheter insertion technique was a more important factor than device design in the initiation of infections. Indeed, none of the studies reviewed in this document have indicated that a modified design of urine drainage system reduces infection rates compared with conventional systems.


During this review, no published studies were found that compared drainage bag connectors with and without ridges. Also, no studies were available that compared 'T' bar valves with 'Flip-flo' valves on the outflow tubes of drainage bags.

Evidence suggests that contaminated drainage bags cause UTI in some cases. None of the newer technological advances mentioned in this review (such as pre-connected catheter/drainage bag systems) appeared to significantly reduce infection rates. As there is no evidence to suggest the benefit of one system over another in terms of infection control, health care workers should base their decisions on practical issues (such as the chances of a patient knocking a 'T' bar open) and 'ease of manipulation'.

These results suggest that catheter insertion and subsequent manipulation of the system are some of the most important factors influencing infection rates and therefore training is one of the most crucial ways in which infection rates can be reduced. All of the issues regarding T-bar design and ridged connectors appear to unsubstantiated.


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