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Repeated gaps in effectiveness occur when using disinfectants. Laboratory L+S shows how to better protect yourself against this.

Have you ever wondered why, despite the use of various disinfectants in hygiene monitoring, critical microorganisms (e.g., bacterial spore formers or molds) are repeatedly detected alongside the typical harmless skin microbes? Have you ever faced an inspector during an official audit who asked for data on disinfectant validation? Or do you no longer want to be satisfied with just good monitoring results, but also want to be prepared for sudden emergencies? Even if it sounds simple: using a listed disinfectant is no longer enough today.

Choosing and qualifying suitable disinfectants in the pharmaceutical environment remains a major challenge. Not only the basic effectiveness of the product against various microorganisms plays a significant role. The disinfectant is also selected based on material compatibility, application safety, and efficiency. Using unsuitable preparations can not only have financial consequences — it also directly impacts product safety if it cannot be ensured that especially pathogenic microorganisms are reliably killed!

Why manufacturer data alone is no longer sufficient

Over the past ten years, numerous disinfectant validations conducted by Laboratory L+S AG have uncovered effectiveness gaps. Sometimes this is due to the use of inappropriate products and strategies, such as using alcohol-based preparations against bacterial spores. On the other hand, manufacturer application recommendations are not always followed correctly. If a disinfectant’s insufficient efficacy is identified during a study, it does not necessarily mean that the product is fundamentally unsuitable.

Products are often tested by manufacturers according to medically relevant criteria, which generally do not reflect the conditions in the pharmaceutical environment.

Especially regarding the spectrum of microorganisms and surface materials, the application areas in hospitals and pharmaceutical industries differ greatly. For this reason, it is crucial to carefully select the test design and have the tests conducted in a laboratory with extensive experience in developing customer-specific test designs for disinfectant efficacy testing.

Selecting the right disinfectants

But it should first start with the initial step: selecting the appropriate disinfectants. To make an initial pre-selection, it is helpful, for example, to refer to the VAH list (Association for Applied Hygiene). The products listed there have been tested by at least two independent experts according to DGHM standards (German Society for Hygiene and Microbiology, now: VAH – Association for Applied Hygiene) for their microbiocidal effect. However, the reference microorganism spectrum and the surfaces used reflect — as already mentioned — the use of disinfectants mainly in clinical settings. Therefore, it is not enough to rely solely on the efficacy data provided by manufacturers. These can be excellent for supplementing one's own data. However, in a second step, it is indispensable to demonstrate the suitability of the respective products for the pharmaceutical environment.

The fact that this is not just a “nice-to-have” is also described in Annex 15 of the GMP guideline. It explicitly requires that cleaning and disinfection procedures for product-contacting equipment surfaces be validated, and if necessary, parts that do not contact the product should also be considered.

The US Food and Drug Administration (FDA) has also been requiring for several years the validation of disinfectant use in pharmaceutical manufacturing and proof of efficacy on operational surfaces against process isolates. In addition to an initial validation to verify disinfectant efficacy, a risk assessment should determine when and how regular revalidations should be performed.

If the disinfectant concept changes — for example, if new disinfectants are added, application concentrations are changed, or new contact times are established — new efficacy tests are often necessary. Especially if the identified native microflora spectrum changes, it is advisable to conduct revalidations.

Presenting conditions on-site more realistically and practically

Since there was a long period lacking binding guidelines for conducting disinfectant validations, the validation officer in pharmaceutical companies had the “black sheep” — in this case, to define suitable methods and requirements within a validation plan. To ensure comparability of results, testing according to DGHM or EN guidelines is recommended. The test design essentially corresponds to the standard methods originally developed for disinfectant manufacturers and still used today by disinfectant producers for efficacy testing.

However, the real conditions in the pharmaceutical environment are not reflected. In a practical surface test according to DGHM guidelines, for example, microbial counts of up to 10^1 CFU/ml are used, and minimum reductions of up to 5 log steps are required. Hygienic officers know, however, that this has little to do with “real microbiological life.” Evaluations of hygiene monitoring show that — if anything — only low microbial counts are usually found, making a reduction of up to 5 log steps exaggerated. This aspect is addressed by USP in chapter <1072> “Disinfectants and Antiseptics”: “... disinfectants are less effective against the higher numbers of microorganisms used in laboratory challenge tests than they are against the numbers that are found in clean rooms.” Accordingly, USP recommends a microbial reduction of ≥ 3 log steps for vegetative bacteria and ≥ 2 log steps for bacterial spores. Using this USP approach makes the actual on-site conditions more realistic and practical, greatly facilitating disinfectant validation.

Of course, this test design does not mean that all disinfectants are considered effective by default. It remains crucial to select preparations according to their application site and scope of activity.

The first demonstration that applying USP requirements for verifying disinfectant efficacy is useful was shown during a validation for Boehringer Ingelheim in 2007 (see publication Matin et al. [2007]: Practical validation of disinfectants in the pharmaceutical environment, Pharm. Ind. 69, No. 11, 1323 - 1326).

In this practical validation conducted according to DGHM methods, all tested disinfectants — regardless of the surface — showed effectiveness gaps. All tests where the required microbial reductions were not achieved were repeated with lower initial microbial counts, considering USP specifications. It was demonstrated that with lower microbial counts, the required reductions could be achieved in almost all cases.