Overview
EN ISO 11138-5:2017 - "Sterilization of health care products - Biological indicators - Part 5" defines requirements for biological indicators (BIs) and associated materials used to assess low‑temperature steam and formaldehyde sterilization processes. The standard specifies test organisms, suspensions, inoculated carriers, BI construction and test methods intended for use in performance assessment, routine monitoring and production control of these low‑temperature sterilization cycles.
Key topics and technical requirements
- Test organisms: Spores of Geobacillus stearothermophilus are the primary test organism; other strains may be used if demonstrated equivalent performance. Several commercially used strains are cited as suitable examples.
- Population and resistance:
- Resistance is expressed as the D value at 60 °C, stated in minutes to one decimal place for each batch/lot.
- For BIs containing G. stearothermophilus, the standard requires a D value ≥ 6 min when tested per Annex A.
- Viable counts and resistance characteristics must be declared in accordance with ISO 11138‑1.
- Carrier and packaging:
- Suitability of carrier materials and primary packaging must be demonstrated (ISO 11138‑1 and Annex B).
- Note: filter‑paper‑based carriers can be unsuitable because formaldehyde chemisorption on cellulose may alter performance.
- Exposure challenge for carrier testing:
- Minimum exposure temperature: ≥ 5 °C above the manufacturer’s stated maximum exposure temperature.
- Maximum exposure temperature: manufacturer’s stated maximum or, if not stated, ≥ 100 °C.
- Exposure time: ≥ 160 minutes - chosen to realistically challenge carrier materials while remaining within practical process limits.
- Test methods and annexes:
- Annex A provides the liquid‑phase method for determination of resistance to low‑temperature steam and formaldehyde.
- Annex B explains the rationale for the chosen test methodology.
Applications and who uses this standard
- Validation engineers and sterilization specialists - for designing and validating low‑temperature steam/formaldehyde sterilization processes.
- Manufacturers of biological indicators and test kits - to produce BIs that meet defined population and resistance criteria.
- Hospital central sterile departments and medical device manufacturers - for routine process monitoring and quality control.
- Regulatory and conformity assessors - to evaluate BI performance claims and compliance documentation.
Related standards
- ISO 11138‑1 - General requirements for biological indicators (production, labelling, test methods).
- Other parts of the ISO 11138 series (Parts 1–4) for different sterilization modalities.
- ISO 14937 / ISO 25424 and ISO 14161 - standards referenced for process validation, control and interpretation guidance.
Keywords: EN ISO 11138-5:2017, biological indicators, low-temperature steam and formaldehyde, Geobacillus stearothermophilus, D value, sterilization validation, carrier suitability.
