How are cleanroom garments validated as sterile for use in an aseptic cleanroom?
Sterilization is a process that is intended to destroy viable forms of microbial life including bacteria, molds, yeasts, viruses, protozoa, and algae (including bacterial spores) to an acceptable sterility assurance level (SAL). SALs were first used in the food canning industry and refer to the degree to which an item is expected to be non-sterile after exposure to a sterilization process. While we use phrases like “terminal sterilization,” we must remember that sterilization is a matter of degree or probability. In a sterilization process, the nature of microbiological death is therefore described by an exponential function, an expression of probability. For instance, a SAL of 10-6means that there is a one in a million chance (probability) that a microorganism will remain after the sterilization process. However, while this probability can be reduced to a very low number, it can never be reduced to zero. ANSI/AAMI ST67:2003 contains a decision tree to be used to determine the SAL for medicaldevices to be terminally sterilized.
Sterilization is necessary when microorganisms are a contaminant. Such cases would include surgery, the implantation of medical devices, or the injection of solutions into the body. Sometimes, the device, instrument, or solution can be sterilized and packaged until it is ready for use. Often, however, sterilization, regardless of method, has a deleterious effect on the product. In such cases, the alternative is asepsis, the prevention of contact with microorganisms. Aseptic processing or manufacturing generally requires the use of a cleanroom and cleanroom apparel. A sterile cleanroom is often called a sterile suite or aseptic cleanroom. These rooms are meticulously maintained in a sterile condition by rigorous housekeeping and special decontamination procedures governed by the FDA and detailed in the Federal Guidelines to Good Manufacturing Practice (GMP). Note: If you see cGMP, the small case “c” stands for “current.”
Cleanroom garments used in aseptic cleanrooms must be sterile. ANSI/AAMI ST67:2003 identifies the sterility assurance levels for terminally sterilized products. Many companies manufacturing products in an aseptic clean-room require all components used in aseptic processing, including cleanroom garments, to be terminally sterilized to 10-6SAL.
There are three typical methods of sterilizing clean-room garments: steam autoclaving, ethylene oxide (EtO), and ionizing radiation (gamma or electron beam). While each has advantages and disadvantages, gamma irradiation is the most popular method used today.
STEAM AUTOCLAVING
Steam autoclaving is the process of attaining sterility by means of saturated steam and pressure. Usually, the object to be sterilized is wrapped in a vapor-permeable (Tyvek™ paper or cloth) bag and subjected to a high temperature and pressure (121 °C at 15 psi for 15 minutes is common). Unlike dry heat sterilization, steam is much more efficient in penetrating and carrying heat to every surface of the object being sterilized. Steam auto-claving is reasonably convenient, fairly efficient, and widely used for general sterilization of materials that aren’t heat, pressure, or moisture sensitive. Surgical instruments and bed linens are examples of materials that are autoclave compatible. Many injectible solutions and plastic implantable devices are examples of materials that would boil away, cook, or melt if subjected to autoclave sterilization. Historically, steam autoclaving was the primary method of sterilizing cleanroom garments. This was something that the customer did on site. There are quite a number of disadvantages associated with this method, however. For instance, auto-claving causes most cleanroom garments to shrink, often up to two full sizes. This is especially true of the older (and now nearly obsolete) taffeta and herringbone garments. Shrinking, aside from the obvious fit problems this would cause, causes puckering and deformation around zippers and seams sufficient to allow viable and non-viable particle excursions. Steam autoclaving also tends to set in wrinkles, making the garment very unsightly, degrade the fabric prematurely, and affect filtration characteristics. It should be noted that there are some cases yet today where autoclaving can hardly be avoided. This is when the garments must be sterilized before being returned to the garment service provider.
EtO
EtO is a sterilization method that saw wide use for many years, especially for sterilizing cleanroom garments. EtO is a gas that kills microorganisms. In use, the wrapped objects to be sterilized are placed in a vacuum chamber where the air is slowly evacuated and replaced with EtO. Later, this gas is evacuated and replaced with air. Unfortunately, the EtO is very dangerous to humans so the product has to undergo an outgassing/quarantine period of up to 14 days while spore strips are incubated and the residual EtO drops to a safe level. EtO is hardly used at all today to sterilize cleanroom apparel. It is not considered safe or state-of-the-art and requires at least one additional week’s supply of garments to accommodate the extended apparel service cycle. Apparel service companies using EtO cannot compete with those that use other sterilization methods that do not require the extended quarantineperiod.
IONIZING RADIATION
High-energy ionizing radiation is the preferred method for sterilizing cleanroom apparel today. It takes two forms: gamma irradiation and electron beam (e-beam) radiation. Since the latter is not being successfully used to sterilize cleanroom garments because of penetration and load density problems, I will discuss only gamma irradiation. Gamma rays are produced by the decay of cobalt 60, a radioactive isotope of cobalt. Gamma rays are electromagnetic radiation of great penetrating power, emitted by the nucleus of the radioactive atom during decay; they are somewhat similar to an x-ray but shorter in wavelength. In use, garments are cleanroom laundered, packaged, and exposed to gamma irradiation at a contract sterilizer. Here, the garments are exposed to gamma rays in a controlled manor until the minimum specified dose has been administered. There are two kinds of contract gamma facilities, continuous and batch. Before garments can be gamma irradiated, however, validation protocol has to be followed to determine the correct dosage, formerly measured in rads and now measured in “grays.” The validation protocol is specified in the AAMI/ANSI/ISO 11137-1-2006 document entitled “Sterilization of health care products – Radiation – Part 1: Requirements for development, validation and routine control of a sterilization process for medical devices.” It is important to accurately determine the dosage required to obtain the desired sterility assurance level for two reasons. First, gamma irradiation is destructive so the minimum specified dose should be as low as practical with the maximum specified dose being as low as practical too. While it is generally known and accepted, for instance, that 25 kilograys (2.5 megarads) are more than sufficient, it is not a good idea to simply specify 25 kilograys without doing the required validation. A good cleaning/disinfecting process might produce a low bioburden (the number and types of viable microorganisms with which an item is contaminated) and permit irradiation at a lower dose, thus extending garment life while still affording the specified SAL. The second reason for accurately determining the gamma dose appropriate to the specified SAL is liability. Someone’s life could be at risk if the dose has not been set properly, or if the process drifts out of control. It is because of the high liability aspect and the constant pressure felt by our customers from the FDA that the cleanroom garment service providers must undergo such rigorous customer audits. This is serious business and the cleanroom garment service providers must be accountable for their claims.
The gamma irradiation sterilization validation protocol starts with determining the bioburden on the sample item proportion (SIP). The SIP is 10% of the product so a process monitor is used that represents a 10% clean-room coverall. This is called a device. Three lots of 10 devices are washed with other contaminated garments, dried with other garments, and packaged. These are sent to an off-site laboratory to undergo an exhaustive extraction for bioburden. The filter used during the extraction is incubated and the aerobic bacteria, mold, and yeast colony forming units (CFUs) are counted for each of the thirty samples and an average is obtained. This number is then multiplied by 10 to determine the number of CFU per device (coverall). A chart in the “ANSI/AAMI/ ISO 11137-2-2006 Sterilization of health care products – Radiation – Establishing the sterilization dose” then indicates a dosage that should produce a biological reduction of ten to the minus two or fewer than two positive devices per hundred samples. A corresponding dose is shown that statistically presumes a higher SAL (if the lower SAL is achieved). This lower number is known as the verification dose and requires that one hundred additional samples be prepared as before and then sent to the contract sterilizer with an instruction to irradiate at the lower verification dose. The samples are then extracted and incubated. If there are two or fewer positive samples per the one hundred sample lot, then it can be statistically presumed that the higher dose on the table will produce its respective SAL — assuming that the process stays in control and no specifics of the process change. A change in the process requires a complete re-validation. Additionally, at the time of validation, a one-time analysis for bacteriostasis/fungistasis and exhaustive bioburden is performed.
The calculated sterilization dose becomes one component of the customer specifications for gamma irradiation of the product. Other factors are the density of the product, the dimensions, and the weight of the product in the transport container used. The contract sterilizer performs a dose mapping of each product. This assures that the correct radiation dose is delivered to the product every time. Dosimeters are placed on the product during the gamma irradiation process. After irradiation, the dosimeters are removed and read using a calibrated spec-trophotometer. The product is released by Quality Assurance based on the dosimetry readings’ compliance with the customer’s specified minimum and maximum gamma dose for the product.
It is incumbent for the supplier of either reusable or disposable clean-room garments to validate its sterile garment program for gamma radiation per ANSI/AAMI/ISO 11137-1-2006, “Sterilization of Health Care Products - Radiation – Part 1: Requirements for Development, Validation and Routine Control of a Sterilization process for medical devices” and ANSI/AAMI/ISO 11137-2-2006, “Sterilization of health care products – Radiation – Part 2: Establishing the Sterilization Dose” to assure its promise to deliver garments sterilized to the contracted SAL by performing dose audits every three months. The device bioburden analysis is performed per ANSI/ AAMI/ISO 11737-1, “Sterilization of medical devices – Microbiological methods – Part 1: Determination of the population of microorganisms on product.” The AAMI sterility analysis is performed per ANSI/ AAMI/ISO 11737-2, “Sterilization of medical devices – Microbiological methods – Part 2: Test of sterility performed in the validation of a sterilization process.” Section 12.1.3.1 in ANSI/AAMI/ISO 11137-1-2006, “Frequency of sterilization dose audits,” states that the frequency of dose audits may be reduced to every six months if there has not been a change in the validated system and all quarterly dose audits have passed in the previous year. If there is a failure, dose audits must be performed every three months. Even if there has not been a change in the validated system, dose audits must be performed at least once a year.
Source: http://www.cemag.us/articles/2007/05/understanding-cleanroom-apparel-sterilization-part-1