Understanding Sterility Assurance Levels

Sterility Assurance Level (SAL) is important in any production operation where there is a threat of contamination that could affect the product (in the case of pharmaceutical manufacturing), the health of a client, customer, or any subsequent user.

The SAL addresses the possibility of bacteria, viruses, spores, or other microorganisms surviving the sterilization process of items such as medical devices, drugs/medications, protective clothing for cleanrooms, and more.

What is the difference between 10-5 and 10-6 SALs?

In the U.S. National Library of Medicine/National Institutes of Health (NIH) journal PubMed, the acceptable levels are as follows: SAL of 10-3 is a designation which applies to low-level sterilization often employed in industry; 10-4 is considered high-level sterilization suitable for heat-resistant medical instruments.

The standard for injectables, or anything that enters the body anywhere other than through the digestive tract, is 10-6. This standard is also recommended for sterile cleanrooms that involve pharmaceutical compounding, consumer drug manufacturing, or highly sensitive aerospace work.

So, what do these numbers actually mean? This article covers how this applies to the health care industry, the food and beverage industry, as well as conventional household cleaning products, and generic categories.

Microbiology 101

Let’s consider an example order for 100,000 single-use units. Presented with a SAL specification of 10-5, and a cost of 13¢ per unit, versus a 10-6 specification, costing 18¢ per unit. The difference between orders will be $500, so why would an administrator choose the more expensive option?

Looking at the Numbers

Let’s say an unprocessed sample has been deliberately contaminated and has one million bacteria on its surface before being sterilized. Assuming each step of sterilization destroys 90% of the bacteria after one treatment, then only 100,000 bacterial remain; after two steps, 10,000 remain; step three leaves 1,000; followed by 100, 10, and finally just 1 bacterium, for steps 4, 5, and 6, respectively.

Each step is called a log-reduction and refers to a decrease by an order of magnitude, which is why each step is referred to by negative exponents; these take the form of 10-1, 10-2, 10-3, 10-4, 10-5, and 10-6.

Achieving a SAL of 10-1 does not mean the object is sterile. It almost certainly is still contaminated because only 90% of the bacteria have been killed. Kill 90% more of the remainder (10-2) and the likelihood is that there is still significant contamination. It is not until a SAL of 10-3 that we can begin to think of something as fairly clean for conventional (non-medical) use.

How is sterility assurance level measured?

What SAL is addressing is the likelihood of survival of a viable microorganism, such as bacteria. A value of 10-5 suggests that only 1 in 100,000 will survive sterilization. 10-6, on the other hand, suggests that the survival rate will only be 1 in 1,000,000.

This distinction becomes extremely important when you’re making sterile dressings by the millions for hospitals. The same is true if you’re making hundreds of frozen TV dinners per minute or bottling 100,000 units of soda pop per hour.

SAL was created because nothing is absolutely certain to be sterile; it is impossible to guarantee 100% sterility. By processing repeatedly, you can be confident that your odds are very, very high against an item being compromised by any surviving bacteria, viruses, spores, or other microorganisms.

Depending on the application, like vials for accepting blood samples, compared to squirt bottles of dish detergent, you would need 10-6 rather than 10-5 to assure testing integrity in the vials. For the squirt bottles, you might require only 10-3, because the detergent itself is toxic to most household microorganisms.

Sterility Assurance Level (FDA)

The federal Food and Drug Administration (FDA) requires all devices that are labeled as sterile to have a sterility assurance level of 10-6. However, if a device is solely used for contact with intact skin, a SAL of 10-3 is suitable.

The FDA recognizes the following standards for the processing of sterile products:

  • ANSI/AAMI/ISO 11135: Medical devices; require validation and routine control of ethylene oxide sterilization (EO sterilization)
  • AAMI/CDV 11137: Sterilization of health care products via radiation
  • AAMI/ISO Technical Information Report (TIR) 13409: Sterilization of health care products via radiation

Medical Devices

Anything designed to exist within a human body, such as a pacemaker or insulin pump, cannot accept a mere SAL 10-5 reduction. It simply wouldn’t be safe, and such a device might even specify a 10-7 level rather than a 10-6. An interior catheter, or cannula, should be sterilized to 10-6, just like a syringe. Even the vials in which drugs are brought into an operating room must be completely sterile on the outside of the container, too.

International Enviroguard’s GammGuard® CE is sterilized to a sterility assurance level of 10-6. Many competitive products are happy to achieve 10-5. However, when it comes to the health and safety of your products, customers, or their customers, do you really want to rely on odds of 100,000:1 instead of 1,000,000:1? Of course not!

The Takeaway

Whether sterilization takes place using thermal effects (heat), photo effects (UV energy), or nuclear effects (irradiation), each level of increasing potency costs energy and time. The current standard for pharmacopoeial sterilization procedures requires a probability of one viable microorganism (or less) in one million sterilized items of the final product and that means a SAL of 10-6.

Don’t settle for anything less. It simply is not worth the risk to your clients, your customers, or your reputation! Whether you need sterile PPE for handling health care products, personal protection when working with dangerous pathogens in a lab or clean room, or for sterility assurance in pharmaceuticals, we have sterile protective clothing to fit your needs.

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