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How is the sterilization process monitored?

Sterilization procedures should be monitored using biological, mechanical, and chemical indicators. Biological indicators, or spore tests, are the most accepted means of monitoring sterilization because they assess the sterilization process directly by killing known highly resistant microorganisms (e.g., Geobacillus or Bacillus species). However, because spore tests are only done weekly and the results are usually not obtained immediately, mechanical and chemical monitoring should also be done.

Mechanical and chemical indicators do not guarantee sterilization; however, they help detect procedural errors (e.g., overloaded sterilizer, incorrect packaging) and equipment malfunctions. Mechanical and chemical monitoring should be done for every sterilizer load.

Mechanical monitoring involves checking the sterilizer gauges, computer displays, or printouts, and documenting in your sterilization records that pressure, temperature, and exposure time have reached the levels recommended by the sterilizer manufacturer. Since these parameters can be observed during the sterilization cycle, this might be the first indication of a problem.

Chemical monitoring uses sensitive chemicals that change color when exposed to high temperatures or combinations of time and temperature. Examples include chemical indicator tapes, strips, or tabs and special markings on packaging materials. Chemical indicator results are obtained immediately following the sterilization cycle and therefore can provide more timely information about the sterilization cycle than a spore test.

A chemical indicator should be used inside every package to verify that the sterilizing agent has penetrated the package and reached the instruments inside. If the internal chemical indicator is not visible from the outside of the package, an external indicator should also be used. External indicators should be inspected immediately when removing packages from the sterilizer; if the appropriate color change did not occur, do not use the instruments. Chemical indicators help to differentiate between processed and unprocessed items, eliminating the possibility of using instruments that have not been sterilized.

Does the Centers for Disease Control and Prevention (CDC) recommend a specific type of chemical indicator?

No. The two categories of chemical indicators are single-parameter and multiparameter. A single-parameter chemical indicator provides information about only one sterilization parameter (e.g., time or temperature). Multiparameter chemical indicators are designed to react to two or more parameters (e.g., time and temperature or time, temperature, and the presence of steam) and can provide a more reliable indication that sterilization conditions have been met. Chemical indicators (no matter what class or type) do not verify sterility and do not replace the need for weekly spore testing.

Are bead sterilizers an effective means of sterilization?

The Food and Drug Administration (FDA) has determined that a risk of infection exists with these devices because of their potential failure to sterilize dental instruments and has required their commercial distribution to cease unless the manufacturer files a premarket approval application. If a bead sterilizer is used, dental health care personnel assume the risk of using a dental device FDA has deemed neither safe nor effective.

What is air removal testing (e.g., Bowie-Dick Test)?

An air removal test is designed to detect inadequate air removal in pre-vacuum sterilizers. Air not removed from the sterilizer chamber prevents steam from contacting the items in a load and therefore interferes with sterilization. Follow manufacturer instructions for how to perform the test and frequency of testing. If a sterilizer fails the air removal test, the sterilizer should not be used until it passes inspection by sterilizer repair personnel.

How often should biological monitoring (spore testing) be done?

A spore test should be used on each sterilizer at least weekly. Users should follow the manufacturer's directions for how to place the biological indicator in the sterilizer. A spore test should also be used for every load with an implantable device. Ideally, implantable items should not be used until they test negative.

What are the next steps if a spore test result is positive?

If the mechanical (e.g., time, temperature, pressure) and chemical (internal or external) indicators suggest that the sterilizer is functioning properly, a single positive spore test result probably does not indicate sterilizer malfunction. Items other than implantable items do not necessarily need to be recalled. However, the sterilizer should be removed from service and sterilization operating procedures reviewed to determine whether operator error could be responsible. Sterilizer operators should repeat the spore test immediately using the same cycle that produced the positive spore test.

If the result of the repeat spore test is negative and operating procedures were correct, then the sterilizer can be returned to service. If the repeat spore test result is positive, do not use the sterilizer until it has been inspected or repaired and rechallenged with spore tests in three consecutive fully loaded chamber sterilization cycles. When possible, items from suspect loads dating back to the last negative spore test should be recalled, rewrapped, and resterilized. Results of biological monitoring and sterilization monitoring reports should be documented.

See Table 12 [PDF-948K] of the Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008 for the suggested protocol to manage a positive biological indicator in a steam sterilizer.

What can cause sterilization failure?

Common Causes of Sterilization Failure

Cause Potential Result
  • Improper cleaning of instruments
  • Protein and salt debris may insulate organisms from direct contact with the sterilizing agent and interfere with its efficacy.
  • Improper packaging
  • Wrong packaging material for the method of sterilization
  • Excessive packaging material
  • Prevents penetration of the sterilizing agent; packaging material may melt.
  • Retards penetration of the sterilizing agent.
  • Improper loading of the sterilizer
  • Overloading
  • No separation between packages or cassettes, even without overloading
  • Increases heat-up time and will retard penetration of the sterilizing agent to the center of the sterilizer load.
  • May prevent or retard thorough contact of the sterilizing agent with all items in the chamber.
  • Improper timing and temperature
  • Incorrect operation of the sterilizer
  • Insufficient time at proper temperature to kill organisms.

Modified from Miller CH and Palenik CJ (2010).

What type of information should be included in my sterilization records?

For each sterilization cycle, record the type of sterilizer and cycle used; the load identification number; the load contents; the exposure parameters (e.g., time and temperature); the operator’s name or initials; and the results of mechanical, chemical, and biological monitoring.

How long should sterilization monitoring records be maintained?

Records of sterilization monitoring (mechanical, chemical, and biological) should be maintained long enough to comply with state and local regulations. The Centers for Disease Control and Prevention (CDC) does not maintain information on time limits for every state but provides an example of 3 years in its sterilization guidelines, which is the time frame used by the Joint Commission inspection agency.


Association for the Advancement of Medical Instrumentation, American National Standards Institute. Comprehensive guide to steam sterilization and sterility assurance in health care facilities. ANSI/AAMI ST79-2010; A1:2010; A2:2011; A3:2012; and A4: 2013. Arlington, VA: Association for the Advancement of Medical Instrumentation, 2010.

CDC. Guidelines for infection control in dental health-care settings – 2003. MMWR 2003;52(No. RR-17):1–66.

Harte JA, Molinari JA. Sterilization Procedures and Monitoring. In: Molinari JA, Harte JA eds. Cottone’s Practical Infection Control in Dentistry, 3rd ed. Baltimore: Lippincott Williams & Wilkins, 2010;148–170.

Miller CH, Palenik CJ. Instrument Processing. In: Miller CH, Palenik DJ, eds. Infection Control and Management of Hazardous Materials for the Dental Team, 4th ed. St. Louis: Mosby, 2010;135–169.

Rutala WA, Weber DJ, and the Healthcare Infection Control Practices Advisory Committee. Guideline for disinfection and sterilization in healthcare facilities, 2008:1–158. Available at: Accessed March 18, 2016.