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A Routine Validation of Microbial Deactivation Process – Why, When and How?

Hila Frank Scientific Project Manager 30.07.2019

Infectious healthcare waste has the potential of containing pathogenic agents. It is accepted worldwide that there are strict regulations required in order to treat this infected waste. If these pathogenic agents are not deactivated to the established recommended level following treatment, the waste can pose a huge risk on public health and the environment.

In order to avoid potential risks that infectious waste poses, the ‘State and Territorial Association on Alternative Treatment Technologies (STAATT)’, established clear standards to define microbial inactivation according to four levels:


Level I – Inactivation of vegetative bacteria, fungi, and lipophilic virus

Level II – Inactivation of vegetative bacteria, fungi, all viruses, and mycobacteria.

Level III – Inactivation of vegetative bacteria, fungi, all viruses, mycobacteria, and stearothermophilus spores at 104or greater; or B. subtilis spores at 104 or greater with chemical treatment.*

Level IV – Inactivation of vegetative bacteria, fungi, all viruses, and mycobacteria and stearothermophilus spores at 106 or greater. This level could also be defined as sterilization.

*STAATT level III was defined as the minimal microbial inactivation level for infectious medical waste, while STAATT level IV is demanded in curtain jurisdictions.


All microorganisms stated above have to be inactivated fully or to the defined extent. However, not all of them should be tested for inactivation. Due to the high risks that these microorganisms pose, furthermore, the test must be ‘tested’ this is known as efficacy (the ability the produce a sufficient deactivation of microorganisms).

In order to test the efficacy of a sterilization process, a microorganism that could represent the deactivation of all other microorganisms’ groups is required. This microorganism should be a pathogen surrogate, and is defined as a biological indicator – representing all microorganisms groups including vegetative bacteria, fungi, parasites, viruses, mycobacteria, and bacterial spores.

The STAATT committee defined the spore forming bacteria Geobacillus stearothemophilus or Bacillus atropheaus and Mycobacterial vegetative bacterial cells as the sole biological indicators, representing all microbiological groups for the evaluation of treatment efficacy.

Efficacy testing of medical waste treatment process should take place initially when the technology is installed, and then routinely once a month according to the STAATT recommendations. It should simulate a “worst case” waste scenario, and challenge the process, therefore sometimes the routine monitoring could also be called a “challenge test”. For example, a high concentration of organic matter could challenge a sterilization process conducted by chemical treatment.

Routine monitoring testing could be qualitative or quantitative. Qualitative test would give a growth/no growth answer, while through a quantitative test an enumeration of the remaining viable bacteria is possible. Using one testing method or another, demonstrating 6log reduction of bacterial spores, treatment can be defined as compiled with STAATT level IV.

More about our routine monitoring and verification kits, can be found in our blog post:

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