Understanding the Reduced Incubation Time (RIT) report

Reduced Incubation Time

Biological indicators (BI) are considered the highest standard for monitoring the sterilization process. BI use spores (the most resistant life form) to verify the sterilization cycle lethality. During the last decade, the sterilization market has faced numerous challenges; such as the need for faster reusable materials’ reprocessing, the development of new medical devices and instruments, the emergence of new technologies for their reprocessing, and the need for new indicators appropriate for their control.

In the face of these new challenges, BI manufacturers have invested their efforts in reducing biological indicators incubation time and thus accelerating the release of the processed material. Today, it is possible to find BIs with a readout time between 72 hours to 15 minutes.

ISO11138-1 states that the incubation time must be validated by the manufacturer of the biological indicator. A method for validating a reduced incubation time (RIT) was published in Annex II of “Biological Indicator (BI) Premarket Notification [510(k)] Submissions” Guidance from FDA. This protocol is appropriated for all types of BIs with a readout time less than 7 days.

Sometimes, customers misinterpret this protocol and assume that they must perform the RIT in their own sterilizer. The RIT study is the responsibility of the manufacturer of the BIs and not the end users. The protocol sets out how to validate the RIT for a BI, but it is the manufacturer who decides how often to perform it.

The guidance requires BI manufacturers to expose a total of 300 BIs (100 BIs from 3 different batches) to partial conditions in the appropriate sterilization cycle in order to produce a mixture of positive and negative results. The manufacturer has to identify a partial sterilization cycle in which 30%-80% of biological indicators survive. A partial cycle is described as a cycle in which all sterilization parameters, except time, are met.

The rapid readout was compared to the 7‐day incubation result to determine the reliability of the rapid result. Result reliability was determined using the statistical term of sensitivity. Sensitivity is a measure of the accuracy of the rapid readout to indicate spore survival after sterilization process failure, in comparison with the indicator response after 7-day incubation.


A false negative is defined as a biological indicator that shows a negative response after the rapid incubation and a positive response after a 7-day incubation time.

In summary, and according to FDA guidance, the manufacturer has to demonstrate that at least 97% of the 7‐day growth visual positives were detected by the rapid readout. In other words, the manufacturer has to demonstrate that the system sensitivity is greater than or equal to 97%.

Terragene has demonstrated a sensitivity greater than 97% in the results of all its indicators with readout time different to 7 days. As an example, the results of the SCBI BT224 (final readout in 20 minutes at 60° C) are shown below:

Bionova® BT224 Self-Contained Biological Indicator
Steam Sterilization Processes
Validation of Reduced Incubation Time – Readout Reliability Summary

Sub-lethal Cycles Incubation Temperature # Indicators Tested # Growth Positives at 7 days # False Negatives at 20 min Sensitivity at 20 min # False Negatives at 48 hours Sensitivity at 48 hours
Cycle 1 60∓2°C 2100 1624 1 99.9% 0 100%
Cycle 2 60∓2°C 2100 1512 2 99.9% 0 100%
Cycle 3 60∓2°C 2100 1364 1 99.9% 0 100%

Each indicator with a readout different from 7 days has a RIT validation study, which the user can request to Terragene and thus have proof of the product accuracy.


  1. ISO 11138-1:2006: Sterilization of health care products. Biological Indicators. General requirements.
  2. ISO 18472:2006: Sterilization of health care products. Biological and Chemical Indicators. Essay equipment.
  3. FDA guidance document “Biological Indicator (BI) Premarket Notification [510(k)] Submissions”, attachment II.

#FAQ What are the main features of EtO sterilization technology?

Parameters for EtO sterilization technology

What are the main features of EtO sterilization technology? What parameters are critical for its success?

Ethylene Oxide (EtO) as a sterilizing agent can be adopted when high temperatures and steam are not supported by the material to be processed. EtO sterilization is a simple, low-cost technology that has the ability to penetrate porous loads and is compatible with the vast majority of medical instruments, but due to its high toxicity, appropriate precautions must be taken.

This process requires the control of 4 parameters: EtO concentration (normally between 450 and 1200 mg/l), temperature (37°C to 63°C), time of exposure (depending on the cycle used) and relative humidity (from 40% to 80%). To understand the relevance of relative humidity (RH%) on EtO sterilization, it is necessary to know how this process works. The microbicidal activity of EtO is the result of alkylation (a chemical reaction) of proteins, DNA and RNA(1). This alkylation interferes with the normal cellular and reproductive processes, which renders a non-viability of affected microbes. Humidity plays a key role in EtO sterilization as it is a critical factor in alkylation chemical reactions and it is the most complex and difficult factor to determine because it influences the proper gas diffusion. Using RH% levels below the recommended lower limit will difficult the sterilization process, as alkylation reactions and proper gas distribution will NOT take place. On the other hand, when working in high percentages of RH (above the maximum recommended) water can (and will) condensate on the surface of the loads being sterilized. Water condensation on the surface function as a barrier for the EtO, hence the sterilization process will fail where condensation occurs. Therefore, it is mandatory to control the proper sterilization process by means of chemical and biological indicators.

At Terragene we offer different solutions for monitoring EtO sterilization processes, for further information visit:

(1) Shintani, H. (2017). Ethylene oxide gas sterilization of medical devices. Biocontrol science, 22(1), 1-16.

🔎 Did you know that Bionova Auto-Readers do not need preventive maintenance?

Bionova auto-readers do not need preventive maintenance

Bionova® Auto-Reader Incubators, including IC1020FR, IC1020FR LCD, MiniBio and MiniPro, do not require preventive maintenance because the system possess an automatic checking test that informs if the equipment presents a deviation from normal performance. Corrective maintenance will only be needed if the incubator alerts of a malfunction.

Equipment must be used according to the user’s manual. The manual includes: instructions on how to use, warnings, storage and operating temperature, energy source specifications, cleaning instructions.

You can download the User´s Manual of each Auto-Reader in the corresponding section on our website:

#FAQ📢 What is the purpose of making a positive control of a given BI?

What is the purpose of making a positive control of a given BI

We assure the correct performance of our BIs for a specified period of time (2 years normally) if properly handled and stored as our specifications indicates.

Due to random factors there might be unexpected false negative results. For this reason AAMI ST79 recommends always using a BI as a positive control (non-exposed to sterilization process) from the same lot number as the one being used for testing.

Did you know that you can evaluate the efficacy of your automatic endoscope reprocessor?

Automatic endoscope reprocessors efficacy

Endoscopes are extremely complex reusable medical devices. Due to their contact with mucous membranes and human tissues, cleaning and high-level disinfection processes prior to reuse must be carried out in order to avoid pathogen transmission.

Endoscope reprocessing involving automatic washer disinfectors requires minimal user intervention and generates highly reproducible washing cycles. It is therefore essential to control the efficacy of these processes in order to ensure compliance with cleanliness standards.

Terragene® launches Lumenia System. A complete line of challenge devices and tests soil to control flexible endoscopes washing efficiency.

Main advantages:

  1. Different configurations according to the different automatic endoscope reprocessors in the market
  2. Its capsules permit the use of two cleaning indicators, one internal and one external.
  3. Compatible with the automatic system for quality control and traceability Trazanto.

More details in the link below:

2019-nCoV #Coronavirus: what is and how to prevent it


Coronavirus refers to a wide family of viruses some of which affect humans and cause a great variety of illness. 2019-nCoV is a new strain of coronavirus first identified in Wuhan (China) in the year 2019. The symptoms of virus infections range from mild to severe and ocasionally could be fatal. Older people, and those with pre-existing medical conditions are more prone to become severely ill due to Coronavirus infection [1].

2019-nCov can be transmitted from person to person after close contact with an infected patient. The spread is primarily through respiratory droplets generated when a person coughs, sneezes, or through saliva droplets or nose discharge.

Prevention is the first barrier to avoid the spreading of the virus. Washing hands frequently, practice respiratory hygiene, maintain at least 1 meter between individuals, avoid touching eyes, nose and mouth; are effective personal measures. Room disinfection is also an important prevention action and hydrogen peroxide has long been used as a disinfectant against viruses, yeasts and bacterial spores. Assuring a proper disinfection process is thus essential [2-4].

At Terragene® we have developed a family of products to assess the efficiency of airborne & surface disinfection through hydrogen peroxide (H2O2). The line is composed of two different Chemical Indicators (ChemSurf: Aerosol and Vapor) and a Biological Indicator (BioSurf). ChemSurf allows the correct monitoring of all critical parameters of the process: time, temperature and H2O2 concentration. Its special 3D design concedes the possibility to evaluate the disinfection process in surfaces with different spatial dispositions. BioSurf is the first fluorescence-based super rapid biological indicator in the market and is fully compatible with all Bionova® Fluorescence Automatic Readers and Bionova® Traceability Software.

[1] World Health Organization (WHO)
[2] Andersen, B. M., Rasch, M., Hochlin, K., Jensen, F. H., Wismar, P., & Fredriksen, J. E. (2006). Decontamination of rooms, medical equipment and ambulances using an aerosol of hydrogen peroxide disinfectant. Journal of Hospital Infection, 62(2), 149-155.
[3] Pottage, T., Richardson, C., Parks, S., Walker, J. T., & Bennett, A. M. (2010). Evaluation of hydrogen peroxide gaseous disinfection systems to decontaminate viruses. Journal of Hospital Infection, 74(1), 55-61.
[4] Heckert, R. A., Best, M., Jordan, L. T., Dulac, G. C., Eddington, D. L., & Sterritt, W. G. (1997). Efficacy of vaporized hydrogen peroxide against exotic animal viruses. Appl. Environ. Microbiol., 63(10), 3916-3918.

WEB-01 Rev.11 22/05/2018