Why sterility testing on its own is not enough to assure sterility

By Andy Whittard

Quality control in pharmaceutical manufacture is essential and requires a combination of tests, protocols and validated processes to minimise risk to public health.

Sterility testing is recognised as the best way to ensure pharmaceutical products are safe for human use at the final point before release. Yet the test is not perfect and should not be used as a standalone guarantee of sterility.

Ensuring sterility begins with facility design and validation. It requires good operator training, well-designed processes and well-considered environmental monitoring protocols, including particle monitoring.

In fact, the sterility test should be regarded as only the final step in a series of protocols that all play a vital part in minimising and identifying contamination of pharmaceutical products.

New call-to-action

Sterility testing alone cannot guarantee a sterile aseptic process

Achieving sterility requires a combination of organisation-wide protocols managed by engaged, trained operators who all adhere to external regulations.

Since 2003, the Medicines and Healthcare products Regulatory Agency, (MHRA) has governed the safety and quality of medicine in the UK, plus all investigations into harmful incidents.

Product recalls are not rare. In January 2019, the MHRA issued an EU-wide, class 2 medicines recall for Irbesartan tablets as a precaution against a possible contamination of N-nitrosodiethylamine (NDEA); a carcinogenic and mutagenic organic compound found in tobacco smoke. They also found traces of a semi-volatile organic chemical N-nitrosodimethylamine (NDMA).

In 2018 alone MHRA published nine recall notices for lack of confidence in sterility assurance and the FDA published four.

The details of each incidence can be found on the following websites:

The UK Government Website



In 2017, Asda and Superdrug had to recall St John’s Wort herbal medicine tablets due to contamination with toxic substances, while in Q1 2018 alone, 84 US pharmaceutical companies reported at least one recall.

Such recalls may be a fact of life for the pharmaceutical industry, but their cost to a business can be notoriously high. In 1982, Johnson & Johnson had the dubious accolade of experiencing the ‘recall that started them all’, when Tylenol contaminated with cyanide made it onto the market. Seven people died, prompting the recall of 31 million bottles of J&J’s best-selling product, costing them over $100 million.

The short story is, sterility testing is here to stay as the best final step we currently have in quality control. But it is certainly not a standalone quality guarantee.

Limitations to the standard sterility test

There are situations in pharmaceutical production where sterility testing fails altogether due to the nature of the medication and the urgency of need by the patient:

Prescribed medication

If the medicine is needed within 14 days, sterility testing is invalid because the test takes at least 14 days to carry out. This is also the case in hospital pharmacies and private commercial enterprises that manufacture medicinal products to order for immediate or short notice patient use.

Antimicrobial medication

If a medicine is designed to eradicate microbes, the product itself will prevent microbial growth and invalidate the test.

Facility design, EM and operator protocol in pharmaceutical product testing

The only way to minimise the risk of microbial contamination is to adopt a combination of methods that address each vulnerability.

Facility design and validation

Good facility design has a lot to do with layout and how it contributes to maintaining your aseptic manufacturing process. Your facility should be designed to support all activities within the environment, allowing ease of operations and sanitisation procedures. Equipment must be easily accessible for cleaning, there must be adequate space for personnel movement and logical material directional flows to minimise contamination risk.

Consider and validate your design for the external areas around your cleanroom as well, and the transitional areas where people move into the manufacturing space. These spaces should also be subject to controls. By ensuring this space remains protected, you are actively reducing contaminants entering the critical processing area.

You need to ensure you choose the right surfaces and finishes that support both sterility and durability. Anti-microbial finishes together with good facility design and maintenance principles all contribute to minimising contamination risk.

Operator training

Your operators within your cleanroom facility are responsible for mitigating risks of contamination but they can also present the highest risk. Inexperienced or poorly trained operators present a serious point of vulnerability in any aseptic process, making their education your top priority.

They should be trained in operating an automatic filling line within your specific pharmaceutical environment. While they may have experience in other environments, it does not automatically mean they are ready to step into yours.

It is important to see this as an opportunity to safeguard your own standards in aseptic techniques. Include training in a downflow cabinet and make sure new operators understand how their behaviour within the cleanroom facility influences air quality. How do you ensure correct gowning up procedure? Where is this protocol documented? This is too important to leave any step to chance.

Your whole team should display a deep level of understanding of Good Manufacturing Practice (GMP). In this way, nothing will come as a surprise when new amendments are made, or new team members come into contact with the GMP Annex 1 which is still in draft revision. Knowing what it means is crucial to understanding your role in the facility and in the overall manufacture of the pharmaceuticals.

Validated processes

Process validation requires the collection and evaluation of data from the start of your process design stage throughout the length of your production line.

The validation of your processes is a requirement of GMP for finished pharmaceuticals and the GMP regulations for medical devices. Process validation falls across four categories:

Traditional process validation
Continuous process validation
Hybrid approach
Design space verification

The precise approach you take will depend on the specifics of your products. Once your processes are validated, you will need to undertake ongoing process verification, where you document evidence that the process remains in a state of control during commercial manufacture.

Consistent environmental monitoring

Having a clear idea of the type of environmental monitoring program your operation needs is critical to achieving sterility. A combination of settle plates and air samplers is recommended for continuous environmental monitoring, ensuring they are placed precisely for optimum data gathering at critical areas of your facility. Every year be prepared to run a full audit on your monitoring processes and align them to the latest regulations.

Sterility testing

The sterility test is one of the most widely used and well-established processes within the pharmaceutical industry. There is an increasing need for bespoke formulations of testing media and method validation as pharmaceutical products continue to evolve.

In order to be as competitive as possible, it is becoming more important for pharmaceutical businesses to seek bespoke solutions for their changing needs. Developing the right testing media for method validation can take some experimentation, so it is also important now for manufacturers to nurture flexible, agile service relationships with their suppliers.

Key protocols that will minimise the risk of a positive sterility test outcome

Audit your facility layout, personnel and materials flow
Audit your environmental monitoring program and make sure you are collecting data from all key areas, consistently
Calibrate your air samplers
Ensure you are using the best possible prepared media for your purposes
Investigate alternative, bespoke formulations
Document all your protocols correctly
Train your operators in all sanitisation procedures and EU GMP guides
Engage an experienced analyst to manage records, samples and risk

NEW! Revised Environmental Monitoring Process and Validation Guide 

How are you going to meet the challenge of the new EU GMP Annex 1? 

Our revised and updated guide helps highlight decisions and actions to ensure you remain compliant. 

Download Guide

We promise that we won't SPAM you.