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Biological Indicators and Implant Loads (CRCST Domain 4: Sterilization Process)

AI fact-checked, not reviewed by a certified technician. Spot an error? Report it. Report an error Outline refs: Sec4 III.A, Sec4 V.E, Sec4 VII.F, Sec4 VIII.B.

TL;DR
  • Steam BIs use Geobacillus stearothermophilus spores. [AAMI ST79; HSPA outline Sec4 III.A]
  • Routine steam BI testing: at least weekly, preferably daily, and in every load containing an implant. [AAMI ST79:2017 (per STERIS summary); CDC Guideline (2008)]
  • Implant loads are quarantined until the BI result is negative, except documented emergencies. [AAMI ST79]
  • A positive BI means: take the sterilizer out of service, notify, quarantine implants, retest, and recall per policy. [CDC Guideline (2008) Table 12; AAMI ST79; facility policy]

Biological indicators (BIs) are the only monitoring tool that directly measures whether a sterilization process killed microorganisms. A BI contains a known population of highly resistant bacterial spores. If the process killed them, the indicator shows no growth after incubation.

The organism

For steam sterilization, BIs use spores of Geobacillus stearothermophilus, which are very resistant to moist heat. (Other methods use other organisms; always use the BI the sterilizer and BI manufacturers specify.)

How BIs are used

A BI is placed in a process challenge device (PCD) that represents the hardest-to-sterilize items. For routine monitoring of a full steam load, the PCD is usually placed on the bottom shelf over the drain, the coldest area, unless the manufacturer specifies otherwise. A control BI from the same lot, not exposed to sterilization, is incubated alongside; it must grow to prove the spores were viable and the incubator works.

How often

AAMI guidance commonly cited for steam: routine BI testing at least weekly, preferably daily, and in every load containing an implant. Qualification testing after installation, relocation or major repair is also required. Verify against the current AAMI ST79 edition and facility policy.

Implant loads

Implants stay in the body, so the consequences of a failure are severe. Loads with implants are monitored with a BI PCD (often with a Class 5 integrating indicator) and the implant is quarantined until the BI result is negative. Early release is only for documented emergencies under policy, with follow-up when the BI result is available.

Positive BI

A positive result may mean the process failed. Remove the sterilizer from service and notify the supervisor and infection prevention. Quarantine or recall any implants from the load, check that the cycle, settings and BI were correct, and retest the sterilizer (CDC suggests three consecutive BI cycles). For steam, CDC says other items do not have to be recalled after a single positive BI unless a malfunction is found; if repeat BIs are positive, items processed since the last negative BI are recalled. Many facilities follow the more conservative policy of recalling back to the last negative BI right away. Follow your facility policy. Load records and lot numbers make any recall possible.

How the CRCST tests this

Expect questions on the steam BI organism, routine frequency, implant quarantine, the purpose of the control BI, PCD placement and the steps after a positive result.

Practice questions

Q1 · D4 · Sec4 V.E · AI fact-checked · Report an error

Which organism is used in biological indicators to monitor steam sterilization?

A. Bacillus atrophaeus (formerly B. subtilis)
B. Clostridium sporogenes
C. Staphylococcus aureus
D. Geobacillus stearothermophilus

Answer: D

Steam BIs use spores of Geobacillus stearothermophilus because they are highly resistant to moist heat. Bacillus atrophaeus is used for ethylene oxide and dry heat. Always confirm the BI matches the cycle per its IFU.
ES: Los indicadores biológicos de vapor usan esporas de Geobacillus stearothermophilus por su alta resistencia al calor húmedo. Bacillus atrophaeus se usa para óxido de etileno y calor seco. Confirme siempre que el IB corresponda al ciclo según sus IFU.
Q2 · D4 · Sec4 VII.F · AI fact-checked · Report an error

A steam load contains an implant. Under standard practice, what should happen before the implant is released?

A. Release it as soon as the external indicator tape and printout show the cycle was met
B. Release it after it cools for 30 minutes, if the chemical indicator inside changed
C. Quarantine it until the load's biological indicator PCD result is negative
D. Release it if the surgeon signs a waiver accepting responsibility for the risk

Answer: C

Implant loads should be monitored with a process challenge device containing a BI. They should be quarantined until the BI result is negative. Early release happens only in documented emergencies under facility policy, with follow-up.
ES: Las cargas con implantes deben monitorearse con un dispositivo de desafío de proceso que contenga un IB y permanecer en cuarentena hasta que el IB resulte negativo. La liberación anticipada solo ocurre en emergencias documentadas según la política del hospital, con seguimiento.
Q3 · D4 · Sec4 III.B · AI fact-checked · Report an error

Per commonly cited AAMI ST79 guidance, steam sterilizers should be routinely monitored with a biological indicator PCD at least:

A. Weekly, preferably daily, and in every load containing an implant
B. Daily for implant loads only; other loads need chemical indicators only
C. Monthly, and in any load that contains an implant or loaner tray
D. Once a year during preventive maintenance and after any major repair

Answer: A

Routine BI testing (weekly, preferably daily) and every implant load is standard. Verify against the current standard edition.
ES: La prueba con IB semanal (de preferencia diaria) y en cada carga con implante es estándar. Verifique la edición vigente.
Q4 · D4 · Sec4 VII.E · AI fact-checked · Report an error

Why is a control biological indicator (not exposed to sterilization) incubated with the test BI?

A. To confirm the spores were viable and the incubator supported growth
B. To double-check the test BI result by exposing a second vial in the load
C. To confirm the incubator temperature was recorded on the daily log
D. To provide a negative reference for comparing the color of the test BI

Answer: A

The control should grow. If it does not, the test BI result cannot be trusted.
ES: El control debe crecer. Si no crece, el resultado del IB de prueba no es confiable.
Q5 · D4 · Sec4 VIII.B · AI fact-checked · Report an error

A routine biological indicator test is positive. What is a key next step?

A. Keep using the sterilizer and repeat the BI test with the next scheduled weekly load
B. Release the load, since the physical monitors and chemical indicators all passed
C. Re-incubate the BI for 24 more hours before telling anyone, in case it reads negative
D. Take the sterilizer out of service, notify the supervisor, follow recall policy

Answer: D

A positive BI may mean the cycle failed. Take the sterilizer out of service, notify the supervisor and infection prevention, quarantine implants, and investigate (correct cycle, settings and BI). For steam, CDC says non-implant items need not be recalled after a single positive BI unless a malfunction is found; you retest in three consecutive cycles and recall back to the last negative BI if the results stay positive. Many facilities recall back to the last negative BI right away. Follow facility policy.
ES: Un IB positivo puede indicar que el ciclo falló. Saque el esterilizador de servicio, avise al supervisor y a prevención de infecciones, ponga en cuarentena los implantes e investigue (ciclo, parámetros e IB correctos). Para vapor, los CDC indican que los artículos que no son implantes no tienen que retirarse por un solo IB positivo salvo que se encuentre una falla; se repite la prueba en tres ciclos consecutivos y, si sigue positiva, se retira todo lo procesado desde el último IB negativo. Muchos centros retiran desde el último IB negativo de inmediato. Siga la política del centro.

Common mistakes

Resumen en español: El indicador biológico (IB) mide directamente si se mataron microorganismos. Para vapor se usan esporas de Geobacillus stearothermophilus. Frecuencia comúnmente citada: al menos semanal, de preferencia diaria, y en cada carga con implante. Los implantes quedan en cuarentena hasta que el IB sea negativo (salvo emergencias documentadas). Un IB positivo = sacar el esterilizador de servicio, avisar, poner en cuarentena los implantes, repetir la prueba y retirar artículos según la política. Siempre incuba un IB control.

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Related topics

FAQ

Which organism is in steam BIs?

Geobacillus stearothermophilus spores.

Can an implant be released before the BI result?

Only in a documented emergency according to policy; otherwise it is quarantined until the BI is negative.