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Published on 1 September 2006

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Effective disinfectant application in cleanrooms

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Karen Rossington
Marketing Manager
Shield Medicare
Farnham
UK
E:krossington@shieldmedicare.com

Asignificant amount of time and money is spent on testing and validating the microbial activity of cleanroom disinfectants. However, the effectiveness of the disinfectant in laboratory tests is not the end of the validation process. The method with which the disinfectant is applied can have a significant impact on the overall effectiveness of the product and subsequent environmental results obtained.

The choice of presentation for different cleanroom areas includes:

  • Ready-to-use disinfectant in trigger sprays, ­aerosols or 5-litre containers.
  • Impregnated wipes of various sizes in pouches, sachets or tubs.
  • Concentrates, powder or tablets to make up into a solution in a bucket.
  • Unit dose concentrates that reduce the risk of dilution error.
  • Fogging or gassing with a suitable agent.

Work surfaces
Trigger sprays and aerosols are commonly used to disinfect work surfaces. While some operators find aerosols more comfortable to use, trigger sprays offer advantages which include an adjustable nozzle so liquid can be dispensed as a jet or a spray, no propellants that require special disposal procedures, and all of the liquid can be dispensed from a trigger spray so there is no wastage.

However, there is a potential drawback with some trigger sprays, as contaminated air can be drawn back into the bottle, compromising the sterility of the liquid. Validation work in the licensed pharmacy unit of the Queen Elizabeth Hospital in Birmingham, UK, identified that a trigger spray alcohol had been contaminated with fungal spores only eight hours after opening.(1)

New trigger sprays are available which aim to resolve this problem by utilising a closed system that prevents returned air from coming into contact with the ­sterile fluid and contaminating it. It is essential that such systems be thoroughly and independently validated to ensure that the system is closed and sterility is not compromised.

Product contact areas
In these critical zones (Grade A or B) the disinfectant must be sterile(2) and its application carefully controlled, because residues and particulates must be kept to a minimum. Low-particulate impregnated wipes offer an ideal solution in these situations. The disinfectant is applied evenly and precisely where required – unlike sprays that can pool in difficult-to-reach areas, leaving residues or causing damage to equipment.

Impregnated wipes are available in individual sachets, resealable pouches or tubs. It is important to ensure that the grade of wipe is sufficient for a critical area and that the wipes can be easily removed from the packaging while wearing gloves without creating particulates.

Walls, floors and ceilings
One of the most time-consuming tasks is the disinfection of large surface areas and mops are the most practical solution. A mop and bucket system is commonly used, but now impregnated mop wipes are also available that can save additional time by eliminating the need to mix concentrate into a solution, thus removing the risk of dilution error. They also eliminate the need to source water of suitable quality for dilution, a major inconvenience which has the potential of contamination if the water source is outside the cleanroom area. Disposal is simplified as there is no need to dispose of unused disinfectant in the drainage system.

Where mop and bucket systems are used, consideration needs to be given to the efficient physical removal of contamination, correct dilution of disinfectant, maintaining the sterility of the system and appropriate storage.

Specific unit-dose concentrates are an ideal means of handling disinfectants for bucket systems. They not only ensure the sterility of the concentrate, but also minimise direct handling before use, thus reducing the risk of dilution errors and spillages.

To avoid recontamination of cleaned and disinfected surfaces, it is preferable that the cleaning solution is isolated from soiled solutions. This objective is difficult to achieve using a single bucket because the dirty mop head must be returned to the bucket containing the disinfectant solution in order to apply more solution to the surface; the disinfectant will thus become contaminated.

Work carried out by Dr Smith of Aston University proved that the use of a multiple-bucket cleaning system can have a significant effect on environmental results.(3) A triple-bucket system ensuring that soiled disinfectant has been rinsed from the mop before it is inserted into the disinfectant solution again has been devised. Bucket 1 contains the disinfectant solution, bucket 2 contains water of suitable grade for rinsing and bucket 3 is empty and ready for waste. The simple application protocol is as follows:

  1. Dip mophead into disinfectant and apply to surface.
  2. Insert mophead into wringer so contaminants are passed into bucket 3.
  3. Dip mophead into water to rinse.
  4. Insert into wringer again to remove water and remaining contaminants.
  5. Dip mophead into disinfectant and reapply to surface.

Dr Smith’s work was carried out over three months, in three different grades of room, comparing a single bucket, a triple bucket with standard hospital disinfectant and a triple-bucket with sterile cleanroom disinfectant. As part of the study, Dr Smith measured the bioburden of the disinfectant solution before and after use for a single-bucket system in three different grades of room. The bioburdens for 10ml of solution were tested using a pharmacopœial method for Total Viable Counts. Results showed that the average number of colony-forming units (CFUs) for used disinfectant in a single bucket system were 158, 326 and 0.4 for the three different grades of room. The triple-bucket system showed no contamination of the disinfectant solution after use in any of the rooms.

Various designs of multiple-bucket system are available and consideration needs to be given to the size of the cleanroom and the storage of the bucket system. Some systems are specifically designed for smaller units and will fit under a bench. The system chosen must be suitable for autoclaving so that it does not introduce contaminants into the cleanroom each time it enters.  A flat mophead gives the best coverage. The mophead covers should be single-use and sterile for use in Grade A and B areas; 100% polyester, polyester/cellulose blends and PU sponge are all used to make cleanroom mopheads and the material should be selected according to the grade of room. The mop frame should also be autoclavable and lightweight, especially if ceilings are very high. A universal joint allows the mophead to be tilted to mop behind equipment. As always, mopping should be carried out to a validated procedure by trained operators. To keep the mop as clean as possible during cleaning, work from the cleanest area to the dirtiest. Therefore, clean ceilings and walls before floors, and wipe ceilings and walls starting at the filters and floors at the furthest point from the door. Mopping should be carried out in overlapping parallel lines, ensuring that no surface remains unwiped.

Summary
A cleanroom may need several different application methods for a disinfectant to ensure the most efficient and effective procedure. Each application method should be validated and carried out by trained operators to a standard procedure.

References

  1. Salvage B. Contamination control at your fingertips. Pharmaceutical Manufacturing International, Autumn 1999.
  2. Eudralex. Volume 4, Good Manufacturing Practice, Annex 1 – Manufacture of Sterile Medicinal Products, 38.
  3. Smith J.Validation of cleaning methods and effects on environmental monitoring.Eur J Hosp Pharm 2005;11:1-4.


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