The reduction factor (RF) - An exampel of wishful thinking?

Background

In the Quality Control (QC) program for cleaning and disinfection of flexible endoscopes at  Copenhagen hospitals we had detected the same micro organisms in samples from flexible endoscopes (obtained immediately before an endoscopy) and in blood cultures from  patients after endoscopy.

• Extensive laboratory evaluations of the Washer-disinfectors (WD) and the used chemical products are available. They indicate an effective reduction of micro organisms.  The effect of the disinfection is described by log-stages reduction of the germs (the reduction factor, RF).
• In a practical cooperation of cold chemical and thermo chemical reprocessing of FE is concluded:

 "The classic idea that a disinfection is carried out successfully if the procedure has succeeded in reducing the germs by 3-5 log-stages does not apply here" (Hyg. Med 1994:19;75-83)

• In the German HYGEA study 49% of 152 endoscopes were found contaminated in high rates in test period 1. ( Z Gastroenterol 2000). WDs and chemical products are also evaluated in laboratory test in Germany.

The question is: Are the condition for using the reduction factor fulfilled?

An example

A FE was contaminated with a test germ in a laboratory evaluation of a WD. Samples are obtained before an after the reprocessing in the WD. The sampling results   were: mean log CFUpredisinf.=6 and mean log CFUpostdisinf. = 2.

In a rapport was concluded: The test germ is reduced by 4 log-stages and mean log RF = 4.

Figure1: A constructed example of an evaluation of a washer-disinfector (b=the slope)
 

The mean log RF is defined as 

• Mean log CFU = mean log CFUpredesinf. - mean log CFUpostdesinf.

In everyday life we use

• Log CFUpostdesinf. = log CFUpredisinf. - Mean Log CFU

Using mean log RF we presuppose, that the relation between log CFUpredisinf. and log CFUpostdisinf. is a stright line with a slope=1.

Questions

Is the relation between log CFUpredisinf. and log CFUpostdisinf.

1. a stright line with a slope = 1?
2. a stright line with a slope = 0?
3. an other relation than above?

We call for a documentation!

 

Cold-chemical disinfection

Definitions

The definitions of clean, critical and high-risk FE are showed at table 1. 10 drops of 20µl (total amount 0.2 ml) were spotted on 5% blood agar.

Table 1: 60 samples from the water channel of two Olympus flexible gastroscopes after manual cleaning and disinfection in a washer disinfector with 2% alkaline activated glutaraldehyde for 10 minutes.

Proliferation of bacteria over night in the gastroscopes	Sampling after	Clean endoscopes 0-4 CFU per 0.2 ml	Critical endoscopes 5-49 CFU per 0.2 ml	High-risk endoscopes >=50 CFU per 0.2 ml
No	Manual cleaning	40 (95 %)	2 (5 %)	0
No	Disinfection	38	4	0
Yes	Manual cleaning	8	1	9
Yes	Disinfection	10	4	4

There were no correlation between CFU before and after disinfection, and conditions for using the RF are not fulfilled.

QC results and conclusions

Samples from the water channels of FE immediately before about 3.000 endoscopies has showing that cleaning and cold-chemical disinfection of FE are satisfactory

• If manual cleaning thogether with the washing program in the WD remove the micro organisms form surfaces of FE.
• If the WD and alcohol flushing of FE channels in combination prevent proliferation of micro organisms over night.

Laboratory evaluation of WDs

Using our protocol for laboratory evaluation of WDs the disinfection of FEs fail if WD doesn’t prevent proliferation of the test strains during storage over night. Test day 4 and 5 are the critical days. The results from day 4 and 5 are weary like results from a in use test.

Links

Nosocomial Infection from contaminated FE