Comparison of the sporicidal activity of a UV-C High Level Disinfection process with three FDA Chemical sterilants

Sporicidal Activity of a UV-C HLD

High Level Disinfection Defined by FDA

The Food and Drug Administration (FDA) defines High Level Disinfection (HLD) as a lethal process utilizing a sterilant under less than sterilizing conditions and killing all forms of microbial life except for large numbers of bacterial spores.5
  • To claim HLD a product/process, according to FDA, needs to demonstrate it kills all forms of microbial life; bacteria, fungi, mycobacteria, virus, and demonstrate a potential for sporicidal activity. Even if this sporicidal activity is obtained for a longer contact time than the recommended use conditions.
  • The chart highlights that Bacterial Spores are, the more resistant microbe group to disinfectants.

Indicates What Level of Disinfection Eliminates all Microbe Groups.1-4

Germitec Chronos High Level Disinfection


  • To achieve ‘Sterilisation’, all viable microorganisms must be killed.
  • While High level disinfectants (HLD) kills all viable microorganisms, except a large number of bacterial spores. However, all spores need to be shown to be killed over longer contact time than the recommended use conditions.
  • The other disinfectants Intermediate level disinfectants (ILD) and Low level disinfectants (LLD) are less effective in killing all microbe groups and no substitute to HLD.


To help select the best HLD product/process it is important to know your sporicidal activity results and the time it takes to achieve them.

In this sporicidal activity study, ultraviolet disinfection technology (Hypernova Chronos, Germitec) was compared against three common FDA chemical sterilants (CIDEX OPA Solution, SPOROX II Sterilizing and Disinfection Solution and CIDEX Activated Dialdehyde Solution) against Bacillus subtilis.6

The microbiology carrier tests are conducted to demonstrate the HLD product/process sporicidal effectiveness. This is achieved based on:

  • European Standards (EN) sporicidal effectiveness is demonstrated by a 4-log (99.99%) reduction
  • The AOAC Official Methods sporicidal effectiveness is demonstrated by a 6-log (99.9999%) reduction. Used by the FDA and TGA (Therapeutic Goods Administration – Australian)

Schematic diagrams of the Hypernova Chronos UV-C disinfection unit (A), carrier (B) and carriers’ hanger (C).

Results & Conclusion


The results indicate that the UV-C disinfection process killed spores within a 90 secs cycle time

  • within a 18 seconds exposure time achieved 4.8 Log (99.99) reduction compliant to the EN standards and
  • within a 84 seconds exposure time achieved 6.2 Log (99.9999) reduction compliant to the AOAC standards.
  • For both standards the sporicidal efficacy was substantially higher than the chemical sterilants used according to manufacturer instructions for HLD.6

For the chemicals tested the reductions obtained after the labelled contact time for a high level disinfection or estimated from the 2 values that flank this recommended use condition are much lower.   

  • CIDEX Activated Dialdehyde Solution achieved between 1.1 to 2.3-log reduction for CIDEX after a 20 minutes contact time at 25°C,
  • SPOROX II achieved a 1.1-log reduction after a 30 minutes contact time at 20°C
  • CIDEX OPA achieved between 0.2 and 0.5-log reduction after a 12 minutes contact time at 20°C.
  • Lawley found that disinfectants that achieve a 6-log reduction of C. difficile spores completely eliminated environmental transmission, whereas those with lesser log reductions were not as successful at reducing transmission.7
  • The Center for Disease Control and Prevention (CDC) estimated that in 2017 there were approximately 223,900 hospitalized patients with C. difficile infections in the US with at least 12,800 deaths.9 In acute care facilities, C. difficile infections result in approximately $4.8 billion in extra healthcare costs due to prolonged hospital stays and readmissions.8,10


This study demonstrated that even if it cannot be tested/approved as a sterilant according to AOAC 966.04, the UV-C unit is much more effective than usual FDA Administration approved chemical HLD products to kill spores in real use conditions.

  • These findings highlight why it is important to provide the effectiveness of the extended conditions results as it would assist the users in selecting the best HLD product/process.
  • FDA Standards for HLD approval should include a test demonstrating the sporicidal activity in recommended use conditions.6

Furthermore, since Hypernova Chronos and Antigermix E1 (AE1) share the same core UV-C technology, the AE1 would achieve a similar sporicidal activity results.



Why High Level Disinfection (HLD) is Neccessary

1. ASUM/ACIPC, Guidelines. Australasian Journal of Ultrasound in Medicine, 2017.
2 .WFUMB, Guidelines. World Federation for Ultrasound in Medicine & Biology, 2017.
3. ESR Guidelines, European Society of Radiology Ultrasound Working Group, 2017.
4. Rutala WA, Weber DJ, et al. (2008) Guideline for Disinfection and Sterilization in Healthcare Facilities, HCPAC,
5. US Food and Drug Administration. Reprocessing Medical Devices in Health Care Settings: Validation Methods and Labelling.
Guidance for Industry and Food and Drug Administration Staff. Washington, DC: US Government Printing Office; 2015.
6. Lionel P, et al. (2022) Comparison of the sporicidal activity of a UV disinfection process with three FDA cleared sterilants,
7. Lawley, et al. (2010) Use of purified Clostridium difficile spores to facilitate evaluation of health care disinfection regimens.
10.1128/AEM.00718-10. Epub
8. Navalkele BD, Bezlotoxumab CT. An emerging monoclonal antibody therapy for prevention of recurrent Clostridium difficile
infection. Biol Targets Ther. 2018;12:11–21.
9. Center for Disease Control. Biggest threats and data. CDC. 2019.
html#cdiff. Accessed 27 Feb 2020.
10. Kyne L, Hamel MB, Polavaram R, Kelly CP. Health care costs and mortality associated with nosocomial diarrhea due to
Clostridium difficile. Clin Infect Dis. 2002;34:346–53.

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